Looks like you touched the main points.
I don't like the battery terminals and nearby wiring – but that shouldn't cause an over-voltage problem (it will cause more of an under-voltage problem).
What is the voltage at battery, when car is at idle and at say 1500 RPM
?
The underhood electrical sees a large variety of temperatures and moisture levels. It is very important to solder all electrical connections and to use heat-shrink wrap to prevent corrosion. Using electrical tape helps but for underhood work, it is not preferred. The battery post is also not a good location for a “battery tap”, either for it is highly likely to corrode in a short time.
In this photo, I see four (yellow) crimped connectors and what appears to be two electrical taped connections.
I should back up a bit. I'm not trying to tell you what to do with your car. I'm only giving my thoughts on trying to fix this problem and what I see working on cars for a long time. Crimped electrical connectors
located underhood, does become a hair pulling problem a few years down the road under normal driving conditions, when trying to find out why something is not working correctly.
In your case, I see five different leads hooked up to the positive battery cable:
- One large one goes to the starter.
- The other large one should go a few inches to a large (white) connector (to disconnect the battery for transport or when inside an office building). This wire is for all electrical functions except for starter power and hazard lights.
- A smaller wire goes to another single connector, for the hazard lights.
- Of the other two wires. I would guess one is for your temporary charging system supply wire and the other is for ignition system or radio (I'm guessing).
Once you get your problem fixed, I suggest taking the main electrical wire and adding a junction box a short distance from the battery. A fellow forum member
@Aspen500 did this to his Aspen.
Fusible Links (post #6)
Not directly related, this forum post shows how F-body battery cables should look and routed.
Positive battery cable replacement. (my post #9).
Note: I recently installed a replacement negative battery cable like one shown (post $9) onto my '86 fifth Ave.
Aspen500 is also an automotive technician and he understands the importance of keeping those electrical connections watertight.
BudW