Troubleshooting fuseable link failure

[ratvon]

I've been working on 68 barracuda for a while now started it up moved around many many times but never took it down the road . I discovered the alternator i just bought wasn't charging, well it had 2 field posts so I ground one everything seemed to be fine so I took the car out for a mile and half drive . I get back shut the car off,later parked in the garage, and this morning now power, the fuseable link burned . So I would like to know why and where to start or any other input would be appreciated. Did that field wire I grounded affect anything? I've seen posts about bypassi g the ammeter my is working fine and really didn't see what is done with the field wire

 

[Mattax]

I'm assuming all you did was ground one of the field terminals on the alternator. That is correct. The later voltage regulator controls the flow by opening and closing the ground. That's why an alternator will have a field terminal that is isolated from the housing. The stock '68 voltage regulator, like you have, controls the positive feed. For those, the field's return can go directly to ground.

Fusible link normally burns because the battery discharged a ton of current, or tried to. A less likely cause is the alternator sent a ton of current toward the starter realy and battery. But your ammeter would have pegged the charge side if that happened.
I think we have a good explanation and diagrams here: Understanding Charging Systems with Ammeter.
Take an ohmmeter and check to see if the wire is grounded. If it is, start disconnecting connectors and testing each segment. Disconnect and check the alternator too. There's a chance the output side (heavy 'Bat') terminal got grounded.
The diagrams on my website should help you, especially the one at the bottom from my '67.

 

[ratvon]

I'm assuming all you did was ground one of the field terminals on the alternator. That is correct. The later voltage regulator controls the flow by opening and closing the ground. That's why an alternator will have a field terminal that is isolated from the housing. The stock '68 voltage regulator, like you have, controls the positive feed. For those, the field's return can go directly to ground.

Fusible link normally burns because the battery discharged a ton current, or tried to. A less likely cause is the alternator sent a ton of current toward the starter realy and battery. But your ammeter would have pegged charge the side if that happened.
I think we have a good explanation and diagrams here: Understanding Charging Systems with Ammeter.
Take an ohmmeter and check to see if the wire is grounded. If it is, start disconnecting connectors and testing each segment. Disconnect and check the alternator too. There's a chance the output side (heavy 'Bat') terminal got grounded.
The diagrams on my website should help you, especially the one at the bottom from my '67.

Thank you very much for your response

 

[whitepunkonnitro]

Fusable link failure is almost always one of two things.
A short at or near the Alternator gauge, or a short in the Alternator itself...bad diode.
Also possible in the headlight circuit, but less likely

 

[4spdragtop]

Burnt up fusible link in 67 cuda. It was a bad alt. (Internal short)
I would do some research on which wire should be grounded and which shouldn't with 2 field alternators

 

[ratvon]

Burnt up fusible link in 67 cuda. It was a bad alt. (Internal short)
I would do some research on which wire should be grounded and which shouldn't with 2 field alternators

Yeah I was wondering if it mattered I noticed one had a copper lead the other didn't which is the one I grounded and I know my ammeter gauge was working good

 

[Mattax]

Thank you very much for your response

You welcome. I suppose it might be worth mentioning that fusible links are relatively slow acting on purpose. They can handle 40 amps for a while (depending on size). But when a battery shorts, it can dump a 100 amps or more - in this case the link will melt quick.

 

[4spdragtop]

I believe it does matter. I defer to Fabo and the electrical gurus when I have electrical issues.
When our fusible link burnt, it happened immediately(within seconds) when we hooked up battery +ve. I spoke to Del/67dart273 on the phone and he was just as quick to diagnose the problem as it was for us to create it lol.
Bad alternator.

Yeah I was wondering if it mattered I noticed one had a copper lead the other didn't which is the one I grounded and I know my ammeter gauge was working good

 

[Mattax]

Yeah I was wondering if it mattered I noticed one had a copper lead the other didn't which is the one I grounded and I know my ammeter gauge was working good

It doesn't matter. I used to have the same question, so hopefully I can now explain it.
The field terminals on the alternator each connect to an end of the copper wire windings.
The field is an electro-magnet. When power is put through the windings, an magnetic field is created. The magnetic force goes up with more power and down with less. The strength of that magnetic force determines how much electricity is generated by the spinning rotor.

Two methods to controlling the field
Positive regulated: One of the field terminals is grounded. The other terminal is supplied regulated power.
Negative regulated: One of the field terminals gets power whenever the ignition switch is on. The other terminal completes the circuit to ground through the voltage regulator.

 

[Mattax]

Burnt up fusible link in 67 cuda. It was a bad alt. (Internal short)

That's could do it, and you're not the only one whose had a alt with in internal short. Some post-mortems would be interesting to see.
When an alternator is working correctly, there is no ground connection on the output circuit. At least I can't think of any off the top of my head. The output circuit consists of the windings that generate a/c power which then goes though the rectifer and to the output terminal (marked Bat).

 

[ratvon]

That's could do it, and you're not the only one whose had a alt with in internal short. Some post-mortems would be interesting to see.
When an alternator is working correctly, there is no ground connection on the output circuit. At least I can't think of any off the top of my head. The output circuit consists of the windings that generate a/c power which then goes though the rectifer and to the output terminal (marked Bat).

I had a local parts store check it they said it was okay now with that internal short show up on that test?

 

[Mattax]

In any event, take a ohmeter and start working along the circuit and you'll find the answer.
If you haven't done this before. A cheap multi-meter will do. Disconnect the battery positive (so you don't accidently put voltage through the meter when its set for ohms). Clip or hold one probe to a good ground. Touch the other probe to remaining wire or into the connector so it touches the terminal. (If its the same as '67, it will be location Z shown here.) A ground will show as low resistance. Disconnect the alternator's output terminal (Bat) and repeat the test. Then its a metter of what you find. For example.
-> Infinate resistance is normal. In which case, check the alternator's output terminal for to see if its internally grounded.
-> But if the ground is in the wiring. Then carefully disconnect the bulkhead connectors to see if the short is in the wire to the alternator or on the inside. If its inside, check the wire from Z to the ammeter, and the one from the ammeter to main splice, and mainsplice to P.

As you do this, remember everything after the fuse box, and the headlight switch, is protected by fuses and a circuit breaker. So no point in looking past those devices.
If it gets confusing, print that diagram or make your own to keep track.
edit IF it melted after the ignition switch was turned on, then it could be a short in the ignition or voltage regulation wiring. Just go through it methodicaly and you should find it.

 

[Mattax]

I had a local parts store check it they said it was okay now with that internal short show up on that test?

I'd like to think so, but best to check it yourself with the ohm meter. Of all the alternator failures I've had (Chrysler, GM and even one 1960 Ford DC generator), that's not one I've had myself. That's why I'm curious to see or hear about some post-mortems.
edit: Tony (whitepunknitro) says he's seen it with bad diodes. I'm not sure if that would be the cause or the effect but would place the trouble in the rectifier.

 

[ratvon]

In any event, take a ohmeter and start working along the circuit and you'll find the answer.
If you haven't done this before. A cheap multi-meter will do. Disconnect the battery positive (so you don't accidently put voltage through the meter when its set for ohms). Clip or hold one probe to a good ground. Touch the other probe to remaining wire or into the connector so it touches the terminal. (If its the same as '67, it will be location Z shown here.) A ground will show as low resistance. Disconnect the alternator's output terminal (Bat) and repeat the test. Then its a metter of what you find. For example.
-> Infinate resistance is normal. In which case, check the alternator's output terminal for to see if its internally grounded.
-> But if the ground is in the wiring. Then carefully disconnect the bulkhead connectors to see if the short is in the wire to the alternator or on the inside. If its inside, check the wire from Z to the ammeter, and the one from the ammeter to main splice, and mainsplice to P.

As you do this, remember everything after the fuse box, and the headlight switch, is protected by fuses and a circuit breaker. So no point in looking past those devices.
If it gets confusing, print that diagram or make your own to keep track.
edit IF it melted after the ignition switch was turned on, then it could be a short in the ignition or voltage regulation wiring. Just go through it methodicaly and you should find it.

Ok thanks I'll try that when I get home tonight

 

[ratvon]

In any event, take a ohmeter and start working along the circuit and you'll find the answer.
If you haven't done this before. A cheap multi-meter will do. Disconnect the battery positive (so you don't accidently put voltage through the meter when its set for ohms). Clip or hold one probe to a good ground. Touch the other probe to remaining wire or into the connector so it touches the terminal. (If its the same as '67, it will be location Z shown here.) A ground will show as low resistance. Disconnect the alternator's output terminal (Bat) and repeat the test. Then its a metter of what you find. For example.
-> Infinate resistance is normal. In which case, check the alternator's output terminal for to see if its internally grounded.
-> But if the ground is in the wiring. Then carefully disconnect the bulkhead connectors to see if the short is in the wire to the alternator or on the inside. If its inside, check the wire from Z to the ammeter, and the one from the ammeter to main splice, and mainsplice to P.

As you do this, remember everything after the fuse box, and the headlight switch, is protected by fuses and a circuit breaker. So no point in looking past those devices.
If it gets confusing, print that diagram or make your own to keep track.
edit IF it melted after the ignition switch was turned on, then it could be a short in the ignition or voltage regulation wiring. Just go through it methodicaly and you should find it.

Ok z on yours bulkhead is j on mine with the bulkhead unhooked the meter on the lowest continuity setting ,black probe on the battery, posisitive unhooked .the only place I got a reading on my meter was the field terminal i grounded .3 and the other field going to the vr 2.4 the alt post,fuseable link wire, and j position for the dash bulkhead ,nothing .On the dash bulkhead Q and N from the ballast going to the key ....nothing Now on the coil side of the ballast I piggyback my electric choke and the ignition side of the ballast I piggybacked the red wire for my pertronix distributor if that makes a difference I had no issues until I ground that field post

 

[Mattax]

It's got to be somewhere. Nothing you checked stands out to me.
To make it easier to follow, attached is a diagram for your 68 with the fuselink gone and the battery and alt disconnected.

.3 ohms from alt ground to engine ground may be normal. Compare the case to the ground your referencing. It will probably also be .3 ohms - in which case the resistance is from the case through the block back to wherever your probe is. (Battery negative cable is a good reference.)

The drop through the field - I don't know. The shop manuals test specs are in terms of power draw. The resistance you are measuring is from the terminal through the brush an contact ring, then through the windings of the rotor and out the other brush to the other field terminal.

You could rotate the alternator to while checking again. It's the output side that I'd be most suspicious of, but so far, nothing is pointing toward the alternator.

No other clues on the wires or connectors? Anything that shows signs of excessive high current (heat) ?
If the ammeter was working and you saw nothing abnormal, then it would seem like the short must have been before the ammeter. Might just want to take a look at the wire from J to the ammeter. Also that there are no other wires that could be touching the ammeter's battery terminal.

You can also check for resistance through the circuit. This would not show a short, but high resistance would suggest a long term problem. A circuit with high resistance draws more current than it was designed for. Over time the heat damage can cause additional breakdown.

It's worth checking the starter relay side of the circuit for a ground. Also the condition of the battery. I wouldn't think the alternator would supply enough current in a short ride to burn the link, but its possible. The ammeter should have been showing massive charging.

Worst case, if you can't track down a short, you can test hot using a circuit breaker. There's a Chrysler MTSC that shows how to do this.
------------------------------------------------------------------
Regulator and Ignition circuits:
Was the check with the switch on? Although the only diff would be the wires to the main splice so I doubt it will make a difference.

Pertronix Ignitor: Where ever they suggest is probably fine. Coil side will have reduced voltage while running, full voltage when starting.

Electric choke: I'd think it would prefer full voltage. Also, I think it would be better to have this on a fused circuit.

 

[Mattax]

Since I've drawn it, here's the 68 wiring all hooked up. You can add your modifications to it, or mark it up to show current flows or whatever you need.

 

[ratvon]

Since I've drawn it, here's the 68 wiring all hooked up. You can add your modifications to it, or mark it up to show current flows or whatever you need.

View attachment 1715099087

 

[ratvon]

Looks like there was a lot of heat at the the bulkhead connection maybe that's where the problem is

 

[Mattax]

Looks like there was a lot of heat st the the bulkhead connection may that's where the problem is

OK. When you're back there see which ones took the most heat. That will provide more clues to nature of the problem.

Also, here's another good reason to check the circuits for resistance. Measure from P to J. High resistance means bad connections or wires in that circuit (J to ammeter to main splice to P). Infinate resistance means something broke or burned through.
You can check other circuits the same way. For example, P to N should have low resistance (when the start switch is in the run position).

If you haven't done it yet, its probably time to disconnect the bulkhead connectors. At least the one connector with power wires. There's a catch on the top and another on the bottom of each connector. Sometimes it helps to use a thin screwdriver to hold each one open while pulling the connector back. Steady force straight back, but a little wiggling it up and down helps break corrosion and dirt.

Once the connector is off you can get a better measurement of the inside circuits. Also you can better evaluate each terminal within the bulkhead connectors. The male terminals are pretty easy to clean, the females are more difficult. It's not too hard to remove the terminals and clean 'em good if needed.

 

[ratvon]

OK. When you're back there see which ones took the most heat. That will provide more clues to nature of the problem.

Also, here's another good reason to check the circuits for resistance. Measure from P to J. High resistance means bad connections or wires in that circuit (J to ammeter to main splice to P). Infinate resistance means something broke or burned through.
You can check other circuits the same way. For example, P to N should have low resistance (when the start switch is in the run position).

If you haven't done it yet, its probably time to disconnect the bulkhead connectors. At least the one connector with power wires. There's a catch on the top and another on the bottom of each connector. Sometimes it helps to use a thin screwdriver to hold each one open while pulling the connector back. Steady force straight back, but a little wiggling it up and down helps break corrosion and dirt.

Once the connector is off you can get a better measurement of the inside circuits. Also you can better evaluate each terminal within the bulkhead connectors. The male terminals are pretty easy to clean, the females are more difficult. It's not too hard to remove the terminals and clean 'em good if needed.

Yeah I already had the bulkhead off and was just checking continuity to ground on everything but J wire where the fusible link goes in is the only place that took heat everything under the dash looks fine except for the female end at J it got hot but not the wire

 

[Mattax]

Yeah I already had the bulkhead off and was just checking continuity to ground on everything but J wire where the fusible link goes in is the only place that took heat everything under the dash looks fine except for the female end at J it got hot but not the wire

If its just J, then its probably related to when the battery was supplying power.
It's probably worth checking for circuit continuity, that will help show if there's a loose or poor connection without having to get under the dash.

When you're ready to start replacing components, the factory diagram shows the Fusable link was 16 gage. If you're going for original appearance, insulation was dark blue.

Crimp the fusible link to Packard 56 (or sometimes called Packard-Delphi 56) terminals for 16 gage wire. Use a good crimper with jaws for "open barrel" terminals. I finally broke down and bought a decent one which comes with a variaty of replacable jaws (Astro branded). Worked great on the females. Unfortunately the jaws are just a little too wide for the male terminals.
here's a close up of open barrel crimp jaws (borrowed from civilianjeep bb: BASIC WIRING 101, Getting You Started! - JeepForum.com)

and a female terminal crimped

To remove the females, use a flattened cotter pin, tiny screw driver, or the tool they make for it to depress the tab while pushing it out. (The double prong version doesn't work well on the some of the mult-wire connectors like the bulkhead. The second prong gets in the way)

To remove the male terminals, you have to squeeze the open part while pushing it out.

The terminals can be often be had at the parts stores. If not, you can mail order from Waytek Wire, terminal supply Company, etc. Or you can sometimes get a few from someone here who has more than the need. I like the tin coated ones.

Before hooking up charge the battery.
Unless you find a smoking gun, have a helper when you do hook up. Be ready to disconnect the battery quick.
Do some voltage checks once its hooked up. Things like: should be battery voltage at the J and P terminals. Watch the ammeter too - should be no flow through ammeter.

If you want to test hot with a circuit breaker before trying a new fusible link, I'll see if I can find that MTSC.
Here it is, They suggest a 5 amp breaker (or a 4-way flasher unit). A test light on it would make it easy to see if power was flowing to a short.
1967 Chrysler Imperial Electrical Accessory Circuit From the Master Technicians Service Conference Session 236

 

[ratvon]

If its just J, then its probably related to when the battery was supplying power.
It's probably worth checking for circuit continuity, that will help show if there's a loose or poor connection without having to get under the dash.

When you're ready to start replacing components, the factory diagram shows the Fusable link was 16 gage. If you're going for original appearance, insulation was dark blue.

Crimp the fusible link to Packard 56 (or sometimes called Packard-Delphi 56) terminals for 16 gage wire. Use a good crimper with jaws for "open barrel" terminals. I finally broke down and bought a decent one which comes with a variaty of replacable jaws (Astro branded). Worked great on the females. Unfortunately the jaws are just a little too wide for the male terminals.
here's a close up of open barrel crimp jaws (borrowed from civilianjeep bb: BASIC WIRING 101, Getting You Started! - JeepForum.com)
View attachment 1715099186
and a female terminal crimped
View attachment 1715099187
To remove the females, use a flattened cotter pin, tiny screw driver, or the tool they make for it to depress the tab while pushing it out. (The double prong version doesn't work well on the some of the mult-wire connectors like the bulkhead. The second prong gets in the way)

To remove the male terminals, you have to squeeze the open part while pushing it out.
View attachment 1715099188
The terminals can be often be had at the parts stores. If not, you can mail order from Waytek Wire, terminal supply Company, etc. Or you can sometimes get a few from someone here who has more than the need. I like the tin coated ones.

Before hooking up charge the battery.
Unless you find a smoking gun, have a helper when you do hook up. Be ready to disconnect the battery quick.
Do some voltage checks once its hooked up. Things like: should be battery voltage at the J and P terminals. Watch the ammeter too - should be no flow through ammeter.

If you want to test hot with a circuit breaker before trying a new fusible link, I'll see if I can find that MTSC.
Here it is, They suggest a 5 amp breaker (or a 4-way flasher unit). A test light on it would make it easy to see if power was flowing to a short.
1967 Chrysler Imperial Electrical Accessory Circuit From the Master Technicians Service Conference Session 236

Thanks for the info I actually have those exact crimpers at work.
I took a male end and a fuseable link from an old harness and soltered it on I'll think I'll get new and start over . I've done a little wiring at work but this is out of my comfort zone. Thanks again I'll try the MTSC

 

[Mattax]

You're about a step a head of me, again! Its great you've got that. A good crimper made life much easier when I replaced a whole bunch of wires and wrap on my jeep last winter.
I've done stuff like that too (take pieces from old harnesses). I just didn't want to post that on the 'net. You're the best judge of condition. Nothing wrong with old - if its in good condition.

Some people hate solder joints, but they have their place. I'm pretty sure I redid a wire connection to the fusible link on my wagoneer with a solder joint. Unlike our mopars, there's no connector between the link and the feed wire. Maybe I should have put one it, but at the time I didn't know enough about how it worked - I just wanted a good connection.
p.s. I thought this guy had some good tips on soldering splices. Connection options, splicing wires and how to do it right, and WRONG!

 

[ratvon]

You're about a step a head of me, again! Its great you've got that. A good crimper made life much easier when I replaced a whole bunch of wires and wrap on my jeep last winter.
I've done stuff like that too (take pieces from old harnesses). I just didn't want to post that on the 'net. You're the best judge of condition. Nothing wrong with old - if its in good condition.

Some people hate solder joints, but they have their place. I'm pretty sure I redid a wire connection to the fusible link on my wagoneer with a solder joint. Unlike our mopars, there's no connector between the link and the feed wire. Maybe I should have put one it, but at the time I didn't know enough about how it worked - I just wanted a good connection.
p.s. I thought this guy had some good tips on soldering splices. Connection options, splicing wires and how to do it right, and WRONG!

Your diagram isn't the same as my 68 I'll PM you what I have