Failures like you have experienced are a result of overcurrent. You are not likely to find one smoking gun for your problem. Every poor connection in the circuit is causing a voltage drop which increases the load on the system.
You need to inspect and clean every connection point in the circuit starting at the firewall connector where the power lead comes into cab. It is also likely your ignition switch has burnt contacts that are ądding to the problem. I've had bad switches on new harnesses cause the same failure.
Here is a thread on the subject and in it is a link to the problem I had.
https://67-72chevytrucks.com/vboard/...d.php?t=818861
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help.
RIP Bob Parks.
1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo
If it breaks I didn't want it in the first place
The WMB repair thread
http://67-72chevytrucks.com/vboard/s...d.php?t=698377