I've fixed the problem I had with 4 volts at my left front turn signal. I swapped wires leading to the park/turn signal lights and all of a sudden I got the correct voltage.

Apparently I had split the front parking light harness and connnected the right parking light to the right turn signal supply wire, and vice versa. I'd say now that I was getting 4 volts due to an 8-volt bleedover from somewhere.

Now both front parking lights work correctly, as well as the front parking lights.

NOW IS WHEN IT GET WEIRD: Although the front lights are fine, I no longer have either rear brake lights or turn signals (either side!)

To check that it wasn't something I had done, I completely un-wired the front lights from the system. Nothing at all except tail lights. *sigh*

I'm not aware that the rear lights have anything to do with the front ones; the rear harness should split off under the dash, so anything done to the front lights (except a direct short, which would drain all the electricity) should not have an effect on the rear lights. Especially the brake lights!

Crawling under the car, there is 12 volts at the brake light switch, and when the pedal is depressed I also get 12 volts at the switch output.

I need to find a wiring diagram to sort this out. I'm taking one step forward and two steps back!