Electrical Help
.......................older automotive electrical systems are not digital,....................simplifying things, but, wiring/circuitry is only battery and ground.
Sometimes, though, it's a little more complicated.
There ARE 'trick' situations where faulty circuits can cause unexpected results due to "backfeed."
For example, I don't remember the "trick" anymore, but someone on the www produced a procedure that they had evidently learned as kids. Left in the car, without keys, they wanted to listen to the radio. I believe it goes something like this:
You turn on the 4 way flashers, hold down the brake, and turn on the radio. These circuits all interact in such a way to backfeed the radio.
Other little tricks involve stuff like dual-filament bulbs that are internally shorted together. This causes stuff like a turn signal will flash all 4 lamps, and turning on the park lights either blows the fuse, or lights all 4 lamps, and then the turn signals won't flash.
THE BIGGEST problem I keep running into with guys cars are the BULKHEAD CONNECTOR, VOLTAGE DROP in the ignition harness (along with headlights) and poor grounds due to rust.
Secondarily, switches and connectors get old, as do the fuse box clips and connections.
An of course in this day and age we ALL think (or maybe do) need a larger alternator
TRUE story. Back in the days "we all" were using 4537's (landing lights) on our 4x4's (AND my RR!!) a guy I knew bought a pair, mounted to the front bumper of his 60's Ferd pick'emup. NO LIGHTS. He finally came into the store, and I went out with a test lamp. The front BUMPER which was bolted directly to the frame, was NOT grounded to the frame due to rust!!!