Hello All,

Working on my "1970 Cutlass Supreme with the 350 rocket"

I have gone through two of the four pin HEI ignition Mods in my HEI distributor and can't figure out why. Definitely burned up based on ohms testing and smell of the component. I have been putting the thermal grease/heat transfer paste on the underside of the module to prevent overheating. When I blew the first one I had the car timed and tweaked with the timing light and had it running fine. As soon as I swapped out a new module the car started right up only to burn the new one out a few days later. I have taken a new 12V+ switch on constant to the distributor, I was never using the old ~9 volt used for the original distributor with external coil. I even put in a new HEI distributor (cheap walmart one) just to make sure my upper body isn't shorting out. The new did the same thing. I know noise on the 12v+ line could cause a burn out or a potential grounding issue on the upper body to block. Where would the best place to properly steal 12v+ I am currently taking it from the fuse box on a 20 amp key on circuit and also have another in-line 20 amp fuse on that 12v before the "Batt+" on the distributor.

Any ideas of what to troubleshoot or a better method of wiring the HEI?

Side note: I also hooked up the tach off the distributor but I can't see how that would make it blow. I will be disconnecting the tach today to eliminate any extra wiring on the distributor to start going through the wiring again.

Thanks,
J

 

I wouldn't power the tachometer and distributor from the same fuse tap. Make sure you're using thermal paste and not dielectric grease.

https://www.arctic.de/us/products/co...l-pastes-pads/

HEI modules are definitely cheap imported electronics, but to have 4 in a row fail.

 

I am using thermal grease not dielectric. I’m just using the stuff that comes with the module made for it. The tach is getting power from the radio and I was never sharing the same 12v for the tach and batt on the distributor. I know the proper way is to hook the distributor batt to the key switch on positive directly. Is anywhere to tap into that 12v without taking apart the steering wheel and hooking up to the ignition switch directly? Can I steal from the ignition plug on the fuse box? Manual shows it as “trunk release” I will attach pictures.

Red wire out is tach power which actually looks like I’m stealing from wiper 10 amp.


thanks J

 

I have not meter out yet but the trunk release on the fuse box if it is 12 V ignition on, I was thinking of hooking up here.

 

Check your grounds- battery to engine and engine to body.

 

my ground from battery to engine is good. Replaced brand new grounding wire. Everywhere else is good with grounds from block. I have from metering a good ground from the upper body on the distributor to the block. I may have had a short in the 12 V on I was using. I just ran a larger gauge wire and I’m gonna isolate the 12 V to the distributor to its own key on from the fuse box. Turns out the trunk release is key on 12v. I’m going to tie into there and test. Since I have a 20a in-line fuse between the dist batt + and where I connect for key on I think I will be safe.

 

X10 on grounds.

Also, what brand and country of origin is the module...It does make a difference.
Davis Unified Ignition (DUI) has the good modules.
https://performancedistributors.com/

 

This is the one I blew. I reworked the 12v and have my cheap distributor firing now. I guess even with an inline fuse I was burning it up with a bad 12v source. Not sure how but new wire and new cheap distributor it’s firing again. Way out of time so I am working on timing it all again.

J

 

attached a picture of the SQR I was using

 

If you're feeling froggy, the resistance wire does provide enough voltage to trip the coil of a standard 5 pin relay. Verify that it stays hot through crank, first.
Or, usually, the 10ga. pink in the ignition switch harness is 12v hot ignition through start.

 

That's where mine has been connected for the past 35+ years.

 

It’s alive off that 12v. TDC but needs some light tweaking!

 

Check the resistance of the primary side of the coil. If it’s too low, the current draw of the coil will be higher than normal and overheat the module.

 

Thank you all! I have her running and not blowing the module now. I definitely had spikes or a short in the 12v line I was using. Ended up using trunk release 12v + key on with a 20 amp in line fuse. Starts right up! Now as for my vacuum lines…. I’ll start another thread for that.

Thanks
J