Ignition Fusible Link Blowing after Lean Burn Conversion

[twood16]

This is a continuation of a saga that started as a really rich condition after the lean burn to hei swap and a 4 barrel Holley.

Wall of Text Forewarning, but short of the long is Ignition Switch Red Fusible link keeps burning if key is left on post GM HEI conversion to delete the lean burn

Car is a 1979 Dodge Magnum with the 318. Very original car and appears to have 64k original miles but who knows.

Starting to bang my head on the wall with this issue that has arisen after removing the Lean Burn System and swapping to the HEI setup following this forum post: Lean burn to old style ign swap?

Crappy Birds-eye photo of the swap:

Minus carb tuning issues everything was going decent. After swapping a leaking power valve I went to start the car and obviously it died due to no fuel in the bowls yet. L had left the key on to go open the garage door and "poof" fusible link wire blows that protects the Ignition Switch (Red) shown below:

Swapped in a dorman fusible link I had on hand randomly and got back to tuning only for the HEI module to die after 30ish minutes of runtime so I bought another one. That night while testing the previous rich condition the car ran out of fuel and with the key on, but not running, the fusible link started to melt and smoke at the ends.

Details of swap:
Took the Dark Blue wire that fed the left side of the ballast resistor and ran that to positive side of coil. Brown wire from right side of resistor to coil is no longer in use and resistor is now out of the car shown below:

Still using an OEM canister filled coil and 7mm wires
Weird thing to note as we thought it would be the same but positive side of the coil is reading battery voltage which is ~14.3 but negative side is ~17. I'm not a big electrical person so maybe this is normal/means nothing

My main question is if anyone has done this swap before and had a similar issue? I tried using an Ohmmeter to test the voltage regulator based on a video I found but my numbers were no where close to the ones in that video. I haven't completely ruled out that the issue came from this swap as the car has been in the garage all winter but was fine the few times I've had to take it out in a pinch and drive it with the lean burn controls still hooked up.

 

[67Dart273]

You need some protection so you can troubleshoot it. One thing I have around here is an old stop/ tail socket, with 1157. You can wire this several ways for testing. Wire both pigtails together, and use that point for one terminal, and the shell for the other. Put that in series with the battery ground for testing. Now you have protection, as the bulb will keep anything from burning up

You also might consider buying a couple of those universal /automotive circuit breakers, maybe a 15 and a 20A. Do the same with them. Now instead of burning up wiring or links, the breaker should sit there and cycle.

Start disconnecting stuff systematically, and I WOULD START with whatever you modified, as that is the likliest source. Next would be the VR, unplug it.

 

[twood16]

Really dumb question as I'm not envisioning this properly I think. So take taillight harness and put it inline where the fusible link that's problematic or right off of the battery?

Or with the circuit breaker, I'm just wiring that in place of the link as well with regular wire correct?

 

[twood16]

Update that may be the answer to my problem. After inspecting under the dash for broken connections and coming up short I went back to wiring diagram and noticed the ignition switch runs through the Oil Pressure Gauge pigtail which reminded me I had tried to move it out of the way when tightening the distributor the first reinstall. I pulled it apart to see this mess:




I cannot confirm that this solves my issue, but based on timeline and being in the same circuit as the guilty fusible link I have high hopes this solved the problem.

Only other question is this. Does the voltage regulator connections look a little worse for wear? There's a sticky substance which I assume is the tar you can see on the backside leaking through maybe? It was sticky enough to make it chore to get the plug off and it broken the raised plastic bit that plugs the Dark Blue wire into the regulator so now I'm waiting on two pigtails and another fusible link to try again. Will update the post when I can confirm or deny this was my issue.

 

[Mattax]

Weird thing to note as we thought it would be the same but positive side of the coil is reading battery voltage which is ~14.3 but negative side is ~17.

AFAIK something is wired wrong, or wrong for that Module, or that module is bad.
The (-) should be switching from ground to system voltage as the engine is running. Its the same as points opening and closing.
With the engine not running, it should be at system voltage and hte module is supposed to control the current (amount of electrons flowing through). If anything is to get too hot with the ignition on and engine not running, its the coil.

I tried using an Ohmmeter to test the voltage regulator based on a video I found but my numbers were no where close to the ones in that video.

That's probably the same wrong youtube information someone posted a while back. If its this one

Your car has a shunted ammeter.
Use that and your handheld multimeter set to DC voltage to determine if the system is being regulated.

The ammeter shows current flowing in or out of the battery. It is scaled roughly 40 amps to 40 amps. Zero in the center.
It should show about 5 amps discharge during start or if you leave the key in run and the engine off.
Much more than that and something is wrong. Something downstream of the key switch is drawing too much current or there is a short.

Engine running, the ammeter should show battery charging after start up, then move to zero.
Measure the voltage at three locations: Across the battery, alternator output, and closest connection you can probe in the regulator's 'sensing' wire. The last is part of the same circuit that powers the alternator rotor, so the blue wire connection on the alternator can be used if nothing else is accessible.

All of those should be within a few tenths of the same voltage.
Furthermore, they should be between 14 and 15 Volts.
And, the votlage should be about the same at 700 rpm, as at fast idle and higher 1200 or 1800 rpm.
If the voltage follows the rpm, then the regulator is not working. That could be hte wiring or the regulator, but now you have narrowed the problem.

If the alternator is producing power above 15 Volts, then the equipment is going to draw more current.
This means the batterywill overcharge (you'll see this on the ammeter), bulbs may burn out quicker, and connections may overheat.

 

[Mattax]

After inspecting under the dash for broken connections and coming up short I went back to wiring diagram and noticed the ignition switch runs through the Oil Pressure Gauge pigtail which reminded me I had tried to move it out of the way when tightening the distributor the first reinstall.

The top of the oil pressure sender is the gage wire connection.
I'm guessing that the three prong is a safety switch for electric choke or other stuff. I would not think it would be the J1 (power feed to switch) but a branch of the J2 (Run) circuit.

 

[Mattax]

So take taillight harness and put it inline where the fusible link that's problematic or right off of the battery?

Tail lights are usually always hot.
Traditionally they get power from the 'always hot' portion of the fusebox.

Your issue is in the J1 feed to the ignition switch. That's what you need to investigate, and where you might want to use a bulb to limit the power through (and light up when there is current flowing) or a breaker that will pop at 10 or 15 amps.

 

[twood16]

The top of the oil pressure sender is the gage wire connection.
I'm guessing that the three prong is a safety switch for electric choke or other stuff. I would not think it would be the J1 (power feed to switch) but a branch of the J2 (Run) circuit.

The 3 prong does tie into the choke as well but is involved in the ignition circuit using the dark blue wire that is split throughout more of the ignition system. The idea is that the light turns on with the key on and once started it stays on until the opposite prong of the two gives a reading to say there is proper oil pressure and thus the light goes out. Since the plug is semi hard to find I am just going to put the gauge sending unit right into the block and bypass the dummy light while I wait for another one to show up.

 

[Mattax]

The 3 prong does tie into the choke as well but is involved in the ignition circuit using the dark blue wire that is split throughout more of the ignition system.

J2 circuit is engine run (usually blue insulated). Traditionally it powers everything critical to running the engine, which includes powering the alternator rotor (aka field).
So that's a branch of the J2.

The idea is that the light turns on with the key on and once started it stays on until the opposite prong of the two gives a reading to say there is proper oil pressure and thus the light goes out.

Typically if there is no pressure gage, then a lamp is used to light up when the pressure is low.
The question is why was there heat generated in the connection.
If its split as you describe, then one terminal out is to the choke - that's somewhat high current, and the other lead is to the indicator bulb, and that should be low current when its on. Be worth looking for shorts.

 

[RustyRatRod]

I just got nuthin. <smh>

 

[Mattax]

I see here the choke control. Was it shorted or drawing too much current?

Coil connections
Your magnum changes the final leg connecting to the coil positive from Blue to Brown and labels it J3.
(That change color coding goes back to the early 70s)

Regardless, its branch off of the run circuit supplying power.
It (coil positive) measured 14 Volts, assuming the alternator was producing at 14 volts, that's fine.
The coil negative connects to a switch inside the ECU, or points, or in your case the HEI.
In addition to switching on/off, the HEI controls the current flow through that wire.

maybe one of the HEI users can describe that more and how it might appear on a voltmeter measurement.

 

[twood16]

Not sure on the choke. While prodding around before I know we didn't have 12 volts to the spade connector to the choke resistor. I know I have more digging to do to double check, but the way I bent the terminals on the oil pressure switch seemed to be the cause of the melting inside the plug. Me leaning on this so hard is that it's the one other thing that I know I touched in the final stages of the swap and I clearly screwed it up. The plug was only half on and jamming that one terminal to the side, possibly grounding out on the switch itself. I'll report back what happens when I bypass the melted switch connector tonight now that I have a new voltage regulator pigtail waiting to be picked up at the parts store this evening.

 

[Mattax]

Well I don't know if there is one problem or two.
In post 5 is the key things needed to begin a diagnoses.
Measure at those three locations and note the ammeter under various conditions and you can figue out what's going on or where to look next.

 

[67Dart273]

You need to troubleshoot by picking 1 problem and trying to solve it, then work on the others. If you cannot solve that one, move to another. I thought sure you might have had something when you were looking at the fuel pump/ oil pressure switch. Unfortunately I don't have documentation on what you are working on.

DISCONNECT questionable stuff and see if you can eliminate the high draw, and if not, leave the loads disconnected. For example, on the ignition circuit, you don't need the choke nor the alternator to troubleshoot that circuit, unless 1 of them is causing the problem, which it could. But disconnec them to see if the problem drops, and if not, leave them off line to not over-complicate the problem. Bear in mind that AKA if what you disconnect was drawing normal current, such as the VR/ alternator field, the load current WILL drop, but it should not "cure" the short/ heavy current problem

Obviously, if you DO have a good diagram, one of the first steps is to document just what all IS on that circuit

 

[twood16]

You need to troubleshoot by picking 1 problem and trying to solve it, then work on the others. If you cannot solve that one, move to another. I thought sure you might have had something when you were looking at the fuel pump/ oil pressure switch. Unfortunately I don't have documentation on what you are working on.

DISCONNECT questionable stuff and see if you can eliminate the high draw, and if not, leave the loads disconnected. For example, on the ignition circuit, you don't need the choke nor the alternator to troubleshoot that circuit, unless 1 of them is causing the problem, which it could. But disconnec them to see if the problem drops, and if not, leave them off line to not over-complicate the problem. Bear in mind that AKA if what you disconnect was drawing normal current, such as the VR/ alternator field, the load current WILL drop, but it should not "cure" the short/ heavy current problem

Obviously, if you DO have a good diagram, one of the first steps is to document just what all IS on that circuit

Currently the only thing I have started to work on and dive into is the Oil Pressure Switch. Oh, and the Voltage regulator only because I ruined the plug when undoing it to do the above "test". I apologize to all if it seems like I'm ignoring all of the information I've been provided as that hasn't been my intention.

I want to resolve the oil pressure switch to either a) be done with this newfound gremlin or b) move on to test other things using the info provided. My ADD brain sees the melted switch that I caused during the swap and admittedly I really hope it's the problem, but that's what I hyper-focused on once I realized it was a mess. This is the diagram that I am seeing to make me believe that at the very least the oil pressure switch is a problem, if not the whole problem. Thank you again to all of the help so far.

 

[twood16]

Just a quick update that it appears my issue stemmed from the poorly connected/bent oil pressure switch. Fusible link has been replaced with new link wire and so far so good after running the car everyday since fixing the link and bypassing the switch.

I appreciate everyone's help/input!