Electrical driving me nuts

Realize how the key/ start circuit/ sequence works

You have TWO circuits for start and run on all these girls

In "run" the ign1 circuit FROM THE KEY goes out through the bulkhead connector (NOT fused, by the way), and depending on year model, feeds power to the ignition system (ballast and ECU box), branches off to feed the VR, alternator field on 70/ later, idle solenoid, electric choke if used, and a couple of smog doo dads up later on

THIS RUN POWER GOES DEAD WHEN cranking.

The ONLY power to the ignition system is from the IGN2 contact in the ignition switch which is live ONLY IN "start." This (usually) brown wire goes out the bulkhead, to the coil + side of the ballast.

THIS WIRE then is the only power to the ignition for cranking

On an electronic ignition , this is a "trick" circuit. This wire goes to the coil side of the ballast and feeds the coil full battery power for start. HOW DOES the ECU get power? This IGN2 power feeds BACKWARDS through the ballast, and from there backfeeds along the what is normally the IGN1 line to the ECU box. This means that during starting, the ECU is ACTUALLY only getting perhaps 5-6V to start. This in fact is normal and how it works

How to troubleshoot?

Check voltages. Clip a multimeter to the coil + terminal and ground, turn the key to "run". You should see NOT full 12V, but somewhere between 4-10V "or so" This is because the coil is drawing current through the resistor and dropping the voltage down

Now check the "start/ crank" condition. With your meter still in place, watch the meter while twisting the key to "start." Now you should see "same as battery." In other words, if the starter drags the battery down to 11.5 during cranking, then that is about what you should read at the coil. You rarely do because of circuit drop. But you SHOULD see AT LEAST 10.5V or more during this test.

Since you are having problems, I'd check these 3-4 times because IE if the key switch contact is flakey, it might show "good" one time and "not" the other

IF THIS voltage does not show good, I'd check the bulkhead/ firewall connector for that circuit, the key switch connector, and the switch itself