This is in my wife's 74 Ramcharger (440/Auto).

I've just finished up swapping in 1 ton axles out of first gen cummins truck and over the last few years I've been working on this truck little by little and it's time to fire it up and drive it out of the garage for the first time in 10 years!

Anyhow, after hooking everything up, when I turn the key forward, to the run position, the coil stars humming. Turning the key to the start position I get no fire and no voltage.

The Ignition 2 Lead is the one that has me really frustrated, it should ONLY have power in the start position and provide power to the coil, instead it's got 8.9V in Run, and no voltage in start.

I've only got one electrical tester, but I think something is backfeeding maybe? I've used two NEW ignition switches and have the exact same results. There are NO modifications to the wiring and no aftermarket anything. I want to make sure everything works 100% before I change anything (planning on ampmeter bypass but that's about it)

I've recently went thru the entire Dash, Forward Light, Rear, and Engine harnesses verifying every single wire for continuity and verified they're in the correct bulkhead position against the 1974 Factory Service Manual. The Dash Harness is out of a 75 Dodge Truck with Factory A/C (all of it's wiring was identical to the FSM), and the Forward Light & Rear Harnesses are out of a 74 W200, and the Engine harness is a NOS M880 harness. Everything in all of the harnesses matched up to the FSM.

I'm hoping someone here has come across a similar issue or perhaps can lead me in the right troubleshooting path.

Due to the ballast resistor you will always have some voltage on the start circuit in run (as a matter of fact that is the side that goes to the ignition system). If you have no voltage to the ignition in start then you have an open between the ignition switch and the engine or you have a bad ignition switch.

That is interesting.
the fact that you have voltage in run says you have continuity.
if you unplug the wires from the ballast, you should see that voltage go away in run.
The fact that you tried 2 switches doesn't mean they are both good.
have you checked for continuity in the switch itself?
have someone hold it in start and see if you have a circuit from power to ign 2.
since they both act the same, you don't even need to pull the one in the truck.

Okay, first things first, is this the ignition setup that you have?

I've never heard a coil hum It is talking to you saying something is goofy, I think
Is your ECU a 4 pin or 5 pin?
What test device are you using?
If it is a volt ohm meter what is your battery voltage with nothing turned on and what is it with the key turned on to the run position and then in the start position?
You can fix this, it is something, wiring, that is not connected correctly

I've heard that a bad ECU can cause coil hum/buzz.

When I say Hum, it's trying to constantly fire, If I remove the plug wire from it, a spark show emerges.

The ECU is a MP Orange Unit, 4 Pin.

I'm using this Ideal tester https://www.idealindustries.ca/products/electrical/electrical-testing/61-746.html

Battery Voltage is 12.9V at the terminals, which I also get unless I'm on the Bypass Circuit/IGN 2 and it's 8.9V

would you have another coil that you could borrow?

I'm going to pull one off another car. (I drove this Ramcharger into my garage 11 years ago though )


Something else I just discovered, when the key is in the "RUN" position, the Fusible Link gets hot FAST...and when I say hot, I don't think they're supposed to get that hot.

I would start looking for a grounded, shorted out, battery feed to a circuit causing a large current draw, hopefully before something melts and catches on fire
You might consider buying and using a small cheap Volt Ohm meter for your testing also, especially on low voltage circuits like your testing

I would try to find out what is heating the fuse link. You could un-plug the regulator and alternator and anything else on the circuit. As far as no fire there are a lot of possibilities. The one thing to be sure of is the ballast resistor connectors. They are indexed so you have to be sure the plugs and the wire orientation are correct. Through the years I have seen the plugs installed wrong due to the index pins being melted off. Simple item to check.

I made some progress today.

The coil wanting to fire fixed itself. That sounds weird, but after bumping the engine over (screw driver across the starter relay terminals), it didn't do that again. Perhaps the distributor was in just the right position that the coil wanted to fire? Is that even possible?

I was able to get the truck running by having the key in run position, jumping the starter relay, and fogging starting fluid into the air cleaner.

I still have NO JOY on the IGN Start or IGN #2 circuits. I'm really thinking I've managed to get two bad ignition switches back to back.

Easy enough to find out. A few year ago I was on a real POS 90s FWD Mopar (forget which model). WOULD not turn over. Ne matter what I did. Replaced the ignition switch, no change. Then I took the switch out and it worked fine. Turned out to be the ignition cylinder not turning far enough. You could have that sort of issue.

Yes, but hard to say it was likely. Coils fire when the electric field inside the coil is charged then de-powered causing it to collapse and the energy released out the coil wire. In short, to fire a coil, you have to turn the voltage on and off, a static distributor SHOULD not do that. However, it is electricity and the ECU could be getting just the right kinda sketchy signal and it freaked. It is the ECU that switches the electricity to the coil on and off.




How are you checking for voltage? I have seen people backprobe the connector and miss the wire thinking it was not a getting power. I prefer to use a OHM Meter or Continuity tester to check the switch when unplugged just to be sure. Another option is to stick a safety pin through the middle wire to get a reading from it. Do not do this on wires exposed to elements like under hood or under the car without sealing the wire afterwards.
You can also check for voltage at the yellow wire on the starter relay when in the cranking position.

Two things can cause a hot fusible link. Excessive current draw or a failing link that is starting to slowly burn away inside. Pretty common on our cars. If you flex the link and the voltage at the fuse block fluctuates, it feels crispy inside or it makes any kind of crunchy noise it is bad. A bad fusible link could cause any number of weird problems including random power loss or coils misfiring when the connection is shotty. They can not be visibly inspected because the insulation is designed to not burn it can look good and be bad.

I found the problem....and made a 12 second video showing what it was...I gotta figure out how to post it...

and yes, two bad BRAND NEW ignition switches in a row, different issues with each.

Might i ask, where were the switches made

I figured out how to upload the video. I posted it as a Product Review to Amazon.

https://www.amazon.com/vdp/f516000a882243e0b9ae5a1a6bc1ebc4?ref=dp_vse_rvc_0


If you'll notice, the start circuit is engaged not in the start position, but in between Run & Start. The other circuits are sending power at odd ball times too telling me that it's clocked wrong on the inside. The replacement switch does the same thing


I opened up a Standard Motor Products switch and an OEM switch, they are designed entirely different but the OEM switch is more simple and has larger contact area's when the different circuits are supposed to engage.