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I would first try one of the electrical connection enhancers such a Caig Deoxit 5.

excellent suggestion

I would test "on the bench" or at the engine bay uninstalled just remember to fuse the 12V supply.

Could you share I procedure? According to the 87 PM partial schematics of the coil driver https://drive.google.com/file/d/0B3qZZUQ9qnBlSlBxek1ReXRiVVU/view
Using pinout...

The good news, its functionality can be troubleshooted without opening it up! When you are ready, LMK and I can help you. I also have a few on the shelf that I can test. I believe they are potted but...

Aries_Turbo suggested using Deoxit D5 (an high end audio contact cleaner) . I bought a can sitting on the shelf ready for action.
https://caig.com/

Transistors will be fine with lower voltages as they are designed to function this way. They do have voltages maximums but it is unlikely your voltage reg can run that high. 35-50V are typically...

I am the only owner of my 87 DD, it is still running the original HEP, coil with wire/distro cap a rotor. The only electrical issue was a faulty Air charge sensor 25 years ago.
Last year I changed...

I have fixed a few "BAD" ones by cutting out the section where the dist cap seals. Resolder and away they go. I believe the reason they break is the lack of strain relief.

That someone was me!! I used a logic analyzer to produce the data.

I would recommend you install the new HEP just to be sure it works as there is lots of aftermarket crap out there

Do you have a procedure for this? I have used both a scope and logic analyzer but I am unsure with a meter.
I assume with a good meter you should see it bounce from zero to 8-9 Volts or so . 5...