CW

I will try to describe this the best I can and hopefully it makes sense. Its my 84 GT with factory fog lights.

When I bought it there was no washer fluid jug so I bought one and put it in the other day. The issue or issues are When the lights are on low beam the two high beam bulbs will light up very dim if you really look at them. If you unplug the drivers high beam the issue goes away on the passenger side. I noticed the ground wire on the drivers side that bolts to the rad support was cut so upon fixing that I noticed that when the ignition is turned to the run position and the head lights are on that ground has some power to it (dim on a test light).
The reason I started looking for issues was that when I turned on my lights today the wipers came on, but only when the ignition is on. While checking grounds and unwrapping the harness looking for any bad wires I thought about the washer jug being the only thing I added since buying the car, I unplugged it and the wiper issue stops but still has the dim high beam and low voltage going through the ground.
My thought is that for some reason its back feeding through the ground and because the washer pump is the closest thing to the grounds at the front of the car its feeding back through that circuit, but I could be way off.
Any ideas what to look for would be much appreciated.

Also I pulled the headlight switch and there is no visible signs of damage or heat to it or the harness.
Another thing, maybe unrelated but since the wires run through the same harness, the tach does not work, all appears to be hooked up but doesnt work. Other factory gauges have been disconnected since I got the car. It did have some bare spots in the gauge sender wires under the hood when I got it but no bare wires anymore.

CW

Update: so after checking the harness, head light switch, and combo switch, as well as going through grounds and disconnecting any added electronics I found the issue.
Feel dumb but it turned out to be the left front park/ signal socket. With a bulb in it and the lights on it would get power to the ground wire too. Pull the bulb it went back to normal. Replaced the socket and it all works again.
Kinda took the long way to a simple fix, but at least I know my harness looks good. Haha!

89StangGTConvertible

Hey man, glad you got it fixed... don't feel bad... most of the time it's some stupid little thing that caused us grief with these older cars. Thanks for posting, maybe you'll save someone else grief that has the same issue.

CW

Ya it never fails, I never think it can be the simple/ cheap things first. Haha!
Im thinking about swapping the sockets to a 3157 style and see if it helps, I dont recall having issues with them like the 1157 seem to have.
Now to get my fog lights working.