Need some electrical help with my ‘68 Plymouth Valiant 100

[snailgarden]

Hey gang, I am new here and was told to get some help from this forum about my issue.

Well the major issue is everything flickers/trembles and it sounds like it is too. At night, the headlights/brakelights, ceiling dome light, dash light all flicker, I notice that the ammeter needle will bob slightly too, it intensifies when driving and it will dip below the halfway mark when I’m in drive holding the brake at a light.

I went to O’reilly’s to have them check out the battery. Apparently, the battery wasn’t bad so to speak, but said it needed a charge. Then I turned the car on so we could check the alternator and there was no reading listed when it was checked.

I’m trying to understand what could be the exact issue. Is it the alternator itself? The regulator? A fuse or ground issue? Like I said, I’m definitely complete novice, so apologize in advance for my lack of knowledge.

 

[4mulas]

Electrical systems can sometimes be tricky but mostly this sounds to me like it may be a bad grounding issue. Check all your grounds for contact and tightm]ness. Also check all your positive connections at the battery, starter solenoid, alternator, ballast, bulkhead connector, and ammeter. You problem likely lies within these areas

 

[snailgarden]

Electrical systems can sometimes be tricky but mostly this sounds to me like it may be a bad grounding issue. Check all your grounds for contact and tightm]ness. Also check all your positive connections at the battery, starter solenoid, alternator, ballast, bulkhead connector, and ammeter. You problem likely lies within these areas

Thank you I will for sure check these out. So another thing, I have ordered an original ‘68 valiant manual, but it won’t be here for probably about a week or so. I’m assuming it will have a diagram showing all of the electrical? Is there a diagram online that I could check out now so I can try to get a head start?

 

[Oldmanmopar]

The first thing I would do is unplug all three bulk heads connectors at the firewall. Clean them with contact cleaner , Put Dielectric grease on them and plug them back in. Also add a ground from the negative terminal to the body. The large positive wire coming from the battery going to the bulk head has a short extension near the firewall called a fusible link. They get corroded inside and at times barely make contact. If you can stretch it at all the fuse wire inside is no good. Its a start .

 

[Murray]

An owners manual does not contain any mechanical/repair information. You will need the FSM= factory service manual.

 

[WV64Signet]

Thank you I will for sure check these out. So another thing, I have ordered an original ‘68 valiant manual, but it won’t be here for probably about a week or so. I’m assuming it will have a diagram showing all of the electrical? Is there a diagram online that I could check out now so I can try to get a head start?

My Mopar has a digital 68 manual for download. There are wiring diagrams in there, it's just black and white so you have to check the legend to follow

Service Manuals – MyMopar

There are laminated, color wiring diagrams that you can also buy, that'll help translate. I did colored pencils to colorize my hard copy TSM

 

[Professor Fate]

Thank you I will for sure check these out. So another thing, I have ordered an original ‘68 valiant manual, but it won’t be here for probably about a week or so. I’m assuming it will have a diagram showing all of the electrical? Is there a diagram online that I could check out now so I can try to get a head start?

By "manual", I hope you mean the Factory service manual, not the Owner's manual.
The FSM will have all the wiring diagrams as well as everything else you need to know about servicing your car.
Available for free download at Service Manuals – MyMopar .

Edit: Boy, I type slow... got treed by 2 guys!

 

[67Dart273]

This type of problem, in addition to advice above, is generally caused by several issues

1. VR. If you still have the OEM electo-mechanical regulator, that alone can cause this
2...Poor brushes / worn/ dirty/ poor contact in the alternator
3...Other problems in the alternator such as loose / shorting stator windings.
4...As mentioned, bad connections in the ammeter circuit, including the ammeter, the bulkhead connector, the eyelet end connectors at the alternator output stud and at the ammeter, and in RARE cases, the welded splice, which is a few inches from the ammeter in the black wire. This splice feeds power to the headlights, to the ignition switch, the fuse panel "hot" buss, and depending on year / model one or two other things

To check for harness voltage drop

Turn key to "run" with engine stopped. Backprobe the IGN terminal of the VR, and stab the other probe into the top of the battery POSITIVE post. You are hoping for a very low reading, the lower the better. over .3V (3/10 of one volt) look for problems in that circuit path. This includes the ammeter circuit mentioned above, plus the ignition switch, the connector for the switch, and the bulkhead terminal feeding the IGN1 "run" voltage (dark blue) through the bulkhead connector.

GROUND DROP. Run the engine at high idle to simulate low/ med cruise RPM. Make this test first with all loads off, and again with lights, heater, etc powered. Stab one probe into the top of the battery NEG post and the other into the VR mounting flange, HARD, to penetrate rust, paint, etc. Once again you are hoping for a low reading, zero is perfect

Improving block to body ground can be a popular problem. Bolt a Ford style eyelet to eyelet starter cable from the rear of the head to the firewall. Sometimes the master cylinder mounting studs work good for that.

If wiring does not seem to be the issue, or improving it does not fix this, I would check the alternator brushes, and (I hate doing this) "throw" a new VR at the car, and most you buy now will not be mechanical, but rather a solid state replacement.

IF YOU buy a new alternator you can use a 70 or later and better yet a "square back" (rectangular heat sink) from about 73 and later, and add one new wire to convert to a 70/ later VR.

On voltage drop in the "run" circuit, one way to work around that is to add a relay in the "run" circuit to take the load off the key. Find the dark blue "run" wire coming out of the bulkhead connector and before it branches off. That wire feeds the ignition system and voltage regulator. Cut the wire where you can work with it, and use the end coming from the bulkhead to activate a Bosch style relay. Feed the relay power from the big bolt on the starter relay with about no12 wire and a fuse or breaker, 20A is fine

The switched contact connects to the engine bay end of the blue wire you cut. This will essentially give the VR a direct path to the battery. You can buy those relays from parts stores with a mountable relay socket and pigtail. Mount it with the wires facing down, so any rain in the bay will tend to drain

Pay attention to the coil polarity on the relay, as most relays of that kind have a diode across the coil. This is for spike/ surge protection when used for other purposes.

 

[Dana67Dart]

Hi SnailGarden, welcome to FABO.

others have posted the MYMOPAR.COM link lots of great info there.

Classiccarwiring.com has laminated full COLORED wiring diagrams. Best money I have spent.

1970 Hamtramck historical has a lot of great info as well
The 1970 Hamtramck Registry Home Page


Google " Chrysler master tech video" you can add a word to the end like "gauges"

And you will get a result of videos like this one:

They are corney BUT very helpful.

I don't know your knowledge of old cars so bear with me.

The alternators on our cars work great at engine RPM over about 1500.

They don't work so good at idle especially at night with headlights and brake lights on.

This is normal and nothing to worry about, ASSUMING all the rest of the electrical system is in good shape.

Some things that can cause flickering in your lights:

1. is a bad diode in the alternator. The alternator produces AC and the diodes convert the AC to DC. If a diode fails it can allow some AC onto the DC wires. This can cause a flicker. The parts store tester should be able to see that.
2. The stock voltage regulator is an electro mechanical device. It has contacts and depending on the load requested by the car will open and close faster or slower. If the regulator is having issues it can produce a voltage fluctuation that would look like a flicker.
3. Grounds as stated before
4. The 3 bulkhead connectors as noted before are a weak spot on our cars. They get corroded and build resistance that makes heat and the heat melts the plastic and weakens the metal terminals.
5. The headlight switch is another location like the bulkhead connectors check & clean
6. The ammeter is a passthrough device. When in good shape it works great, but it can get internally damaged and the connections get weak and build resistance & heat etc.
7. Some remanufactured alternators use a 3" dia pulley when the factory calls for a 2.5 to 2.75. this slows down the alternator and exaggerates the low RPM performance.

Hope this info helps

 

[snailgarden]

An owners manual does not contain any mechanical/repair information. You will need the FSM= factory service manual.

It is the service manual that I ordered.

 

[Dana67Dart]

It is the service manual that I ordered.

If you can return it, do, you can get the FSM free in PDF format at My Mopar.

 

[snailgarden]

Hi SnailGarden, welcome to FABO.

others have posted the MYMOPAR.COM link lots of great info there.

Classiccarwiring.com has laminated full COLORED wiring diagrams. Best money I have spent.

1970 Hamtramck historical has a lot of great info as well
The 1970 Hamtramck Registry Home Page


Google " Chrysler master tech video" you can add a word to the end like "gauges"

And you will get a result of videos like this one:

They are corney BUT very helpful.

I don't know your knowledge of old cars so bear with me.

The alternators on our cars work great at engine RPM over about 1500.

They don't work so good at idle especially at night with headlights and brake lights on.

This is normal and nothing to worry about, ASSUMING all the rest of the electrical system is in good shape.

Some things that can cause flickering in your lights:

1. is a bad diode in the alternator. The alternator produces AC and the diodes convert the AC to DC. If a diode fails it can allow some AC onto the DC wires. This can cause a flicker. The parts store tester should be able to see that.
2. The stock voltage regulator is an electro mechanical device. It has contacts and depending on the load requested by the car will open and close faster or slower. If the regulator is having issues it can produce a voltage fluctuation that would look like a flicker.
3. Grounds as stated before
4. The 3 bulkhead connectors as noted before are a weak spot on our cars. They get corroded and build resistance that makes heat and the heat melts the plastic and weakens the metal terminals.
5. The headlight switch is another location like the bulkhead connectors check & clean
6. The ammeter is a passthrough device. When in good shape it works great, but it can get internally damaged and the connections get weak and build resistance & heat etc.
7. Some remanufactured alternators use a 3" dia pulley when the factory calls for a 2.5 to 2.75. this slows down the alternator and exaggerates the low RPM performance.

Hope this info helps

This was all extremely helpful information. Thank you I did order that service manual, but I just requested to see if I could cancel it.

I will check out the wiring, but -if- I had to replace the VR, how do I figure out which amp I would need specifically? I’m finding ones that are 35 or 46 amp and 60 amp.

 

[WV64Signet]

This was all extremely helpful information. Thank you I did order that service manual, but I just requested to see if I could cancel it.

I will check out the wiring, but -if- I had to replace the VR, how do I figure out which amp I would need specifically? I’m finding ones that are 35 or 46 amp and 60 amp.

Hard copy or digital.. Personal preference

This is how I updated my 64 Service manual using colored pencils and following the legend on the page

For me, it helped me to understand the wiring and routing. I was very new to classic auto work and it suited my learning style.

Most of these cars have had many hands in them over the years. Things are not always as they appear... Especially with wiring.

Great advice provided above.

 

[Professor Fate]

Don't worry about returning it- if you're like me, I prefer to have an actual hardcopy manual sitting in front of me- dog eared pages with greasy thumbprints and all. The digital copies are nice, and sometimes are our only option; but nothing beats a "book on the shelf" for me.

 

[Dana67Dart]

but -if- I had to replace the VR, how do I figure out which amp I would need specifically? I’m finding ones that are 35 or 46 amp and 60 amp

There are not too many options for VR
there are electro mechanical ones and electronic versions of the electro mechanical ones.

As for amperage, whichever one you buy will be fine. Originally the alternator was max output 35 (higher with AC or taxi/police)

The replacement alternators available today will most likely be in the 60 amp range.

So the VRs of today are designed to handle it.



Now for the $10,000 question....

Is your charging system stock for 68?

Post some photos of your VR and the back side of your alternator.

 

[snailgarden]

There are not too many options for VR
there are electro mechanical ones and electronic versions of the electro mechanical ones.

As for amperage, whichever one you buy will be fine. Originally the alternator was max output 35 (higher with AC or taxi/police)

The replacement alternators available today will most likely be in the 60 amp range.

So the VRs of today are designed to handle it.



Now for the $10,000 question....

Is your charging system stock for 68?

Post some photos of your VR and the back side of your alternator.

Does it matter if I get an electro mechanical one or an electrical one? Does the electrical one work just fine?

I’ve attached a photo of the regulator, one picture is of the alternator, I noticed these taped wires by it that seem… possibly sketchy? Also included more of the wires because I’m unsure if these look okay or not.

Also, I just barely discovered today that the back brakes are leaking brake fluid and the intake gasket is leaking antifreeze

 

[snailgarden]

Hard copy or digital.. Personal preference

This is how I updated my 64 Service manual using colored pencils and following the legend on the page

For me, it helped me to understand the wiring and routing. I was very new to classic auto work and it suited my learning style.

Most of these cars have had many hands in them over the years. Things are not always as they appear... Especially with wiring.

Great advice provided above.

View attachment 1716330695

Thank you for this!!!