Found this on the Rock Auto newsletter:
|Repair Mistakes & Blunders|
I have a 1984 Ford F250 that has been through several owners and needed a lot of things fixed. The turn signals did not work, so I decided to replace the turn signal switch. I crawled under the dash with the driver's door open to discover years of “rewiring.” I found all the wires I needed, and with my voltage tester I found a "hot" 12V wire hanging down that I used to power the new turn signal switch.
After installing the switch, I tested all the signals, checked the taillights and front indicator lights and they all worked great. I hopped in the truck to test drive and noticed nothing worked. I got out with the turn signal lever in the “right turn” mode and saw the front and rear turn signal bulbs were now working. I jumped in, closed the door, and no turn signal again.
After some head-scratching and research, I discovered my “hot" wire was connected to the door switch; the circuit that at one time operated the interior cab light. So every time I would open the door, the switch would receive power and the turn signals would work. Closing the door would turn the power off to the switch.
Next up – fix the speedometer.
Steven in Idaho