Ewwwwwww.

They coated the boards. "Conformal coating" it's called. Looks like every place the coating wasn't perfect, the metal underneath corroded.

So the P.O. commuted underwater to get to work every day?? ☺️

Before you get too far you might as well find the ECU. The brain box. It's over by the driver's left leg, behind the kick panel. It controls the injectors. Unless you're planning to run carbs.

I pulled the computer out and took it apart. It looks really good, so I put it back together and started on the ignition module replacement.

I followed this diagram that I got from the knowledge base and tried it out, but no joy.

I didnt see anything about needing to run it through the ballast resistor, so I left it out of the new circuit. Im not sure which side is + on the coil so I put the new green wire where the old one was.

I found another post that had a resistance measurement for the pickup coil. Looks like its suppose to be around 720ohms. Ill check that next time im out.

Im sure im missing something, but im was too tired to really use my brain.

The module is bolted to the throttle body temporarily. And I broke out my new plug wires as well.

Anyone have any suggestions?

some new updates on my ignition woes and HEI module upgrade. Tested resistances on anything I currently have knowledge of. Near as I can tell, everything is as it should be.

I tested both coils that I have using the method listed in the video below. I'm a sucker for detailed documentation and I had a hard time following some of the posts I found. So hopefully this will help others.

The initial test was to test the resistance of the tester itself and it turns out mine needs a little recalibration. Not a huge deal as I understand that I just need to subtract the value from the readings that I take. It turns out that I am off by 1.6 ohms. It is a 30 year old meter though that I inherited from my dad.

The readings on the new coil.

3.1 ohm (1.5ohm corrected) between the + and - terminals and 11,280 ohms between the positive and center.

I purchased this (amazon) coil. It is suppose to be a stock replacement.

Pretty similar readings on the old coil. I kinda figured the old was was good, but meh, why not replace it just in case.

2.2 ohm (.6 ohm corrected) between the + and - terminals and 14,450 ohms between the positive and center.

Also tested resistance on the pickup coil in the distributor and it reads about 675 ohms. According to this post by Zedhead it should read around 720ohms. I feel like this reading is acceptable.

I checked the voltage to the positive side of the coil with the ignition on (white w/ black stripe) as well as suggested by Fastwoman in this post. As well as the battery itself which is new but i have to get a charger on it.

The voltages with the ignition on and off were practically identical.

With that aside, im now looking into the wiring for the new HEI module.

There are tons of articles on this, but it seemed hard for me to find the info I needed, which was wiring the module. Nearly all the posts had the basics, but there was a lot of discussion about using/not using the block resistor and/or a different coil. Couple that with the myriad of wiring diagrams I ran into. It was hard to determine what was proper.

At the moment I am attempting to use a stock coil with a HEI module.

Here are just a few of the discussions I looked at.

GM HEI Module Install by Scanf

Fitting a HEI Module in a Transistor Ignition Unit 1977 280z

This was the most promising diagram I could find as listed in the second link. My confusion seems to be around what I have vs what is shown here. This diagram is also identical to what I have in the FSM

One issue I have with the FSM is that the wire colors don't match. But I am also not 100% this is the original wire loom yet. or maybe Im just not smart enough to decern what the wire color short hand is.

Could it be possible that my condenser is on the wrong terminal. Im hesitant to just start moving and trying different wire combinations without some confidence that what I am doing is correct with the fear of making matters worse.

Below is what I tried for the ignition module wiring last week. As I am writing this post I just noticed that I have the positive and negative wires backwards. If I am not mistaken, I still should be able to get some kind of spark out of it. There is another issue I'm concerned with. See more below.

So now I know that the coil wires are backwards. but my other concern is weather or not I need to run the wires through the block resistor. I feel like by writing this post and working through my explanation, I should be. Instead of wiring the new module directly to the coil as shown in the following diagram that is listed in first link. (also happens to be the same post listed in the knowledge base). I should be unmodifying the existing wiring and attaching the leads to the corresponding terminals on the block resistor as shown below.

Assuming I am correct, Now the only unresolved issue is where the condenser is suppose to be. According to the FSM its suppose to be connected to the center terminal?

How is my logic so far?

On 11/12/2025 at 12:51 PM, nowak1981 said:

tried it out, but no joy

I would add some details of how, exactly, you are evaluating "spark". With a spark plug at the end of a plug wire, through the coil center terminal, with a spark tester...? Are you cranking the engine when you do this? Have you disconnected the original module by the fuse box or did you resintall it?

And, or, but, I have noticed that you do not have any battery power going to the coil in your picture. You only have the coil connected to the module and no pwer to the module either.

You need power to the coil positive terminal.

Also, use your meter and make sure that the mounting screw of the module has a good ground. And make sure that it's the correct screw. Only one of the screws completes the ground through the module, it has a thicker ferrule. Looks like you have the correct screw but you might not have good contact through that screw head or where it seats on the TB. The TB is not the best place to mount it. That's where all of the coil current flows when the module is doing its thing.

And, it you plan to run it for long you need a proper heat sink under the flat part of the module. It gets hot and heat will cause them to fail.

Edited 17 hours ago17 hr by Zed Head
+ one

Just leave the condenser disconnected. You don't need it for now.

You can also just connect both of the wires from the ballast resistor (the block) to the coil positive. You don't need it when you use the HEI module.

1 hour ago, Zed Head said:

And, or, but, I have noticed that you do not have any battery power going to the coil in your picture. You only have the coil connected to the module and no pwer to the module either. You need power to the coil positive terminal.

This makes 100% sense.

As far as the other questions

1 hour ago, Zed Head said:

I would add some details of how, exactly, you are evaluating "spark". With a spark plug at the end of a plug wire, through the coil center terminal, with a spark tester...?

When I tried it last week I had the coil wire attached and one spark plug lead with a spark plug at the end laid on the block, not the best I know. I was mainly looking for any indication to get moving in the right direction. The car came with an inline spark tool.

1 hour ago, Zed Head said:

Are you cranking the engine when you do this?

I am cranking the engine with no spark plugs in the block. I am cranking with many full rotations as I am aware that I will only get spark as the rotor makes the connection. Am I missing something? I'm not a legit mechanic and this is the only way im aware of. Is there another procedure that I'm that Im not aware of?

1 hour ago, Zed Head said:

Have you disconnected the original module by the fuse box or did you resintall it?

The old module is not installed. From the reading I have done, this is the way

1 hour ago, Zed Head said:

Also, use your meter and make sure that the mounting screw of the module has a good ground. And make sure that it's the correct screw. Only one of the screws completes the ground through the module, it has a thicker ferrule. Looks like you have the correct screw but you might not have good contact through that screw head or where it seats on the TB. The TB is not the best place to mount it. That's where all of the coil current flows when the module is doing its thing.

and, it you plan to run it for long you need a proper heat sink under the flat part of the module. It gets hot and heat will cause them to fail.

The module location is definitely temporary and is mounted through the hole with the large ferrule. My initial thought was to cut up the old module housing and is it as a heat sink or perhaps find an old heat sink from a PC. The PC option seems the best solution, but I haven't given it a ton of thought yet. I think they make heat sinks specifically for these modules as well.

1 hour ago, Zed Head said:

Just leave the condenser disconnected. You don't need it for now.

When you say this, it sounds like I will need it in the future? Is there a reason why I would leave it disconnected for now? Am I correct that the condenser is on the wrong terminal?

Edited 15 hours ago15 hr by nowak1981

It doesn't really matter which terminal has the condenser attached. It's there to stop electrical noise.

Winner winner chicken dinner, we have spark

Now im gonna look into some heat sink and stew on where i want to mount it.

Time to move on to the fuel system. I know the fuel is toast and the tank will need to be cleaned. I’ll probably start on removing that and see what condition the lines are in.

I’m excited!