JFinnell

Greeting,

I have been trouble shooting my backup light switch on my 70 914 for the last two months. I have inspected the switch and pin, light bulbs, fuses, and visible wiring. My blinkers and other lights are working properly.

I tested the backup light by touching the two wires together...the backup light did not illuminate. I saw no visible difference between the old and new pins, and the new switch did not solve my problems.

How can I test other parts of the wiring to get the backup light switch to work? Should current run through the switch wires when in reverse. From where do the lights receive current?

Thanks for the help!!

Joe R

I think there are a few more places that I would look at. First is there power on either one of the wires going into the backup light switch. If yes then check continuity of the switch when in reverse.

Ed Morrow

The lights should come on when you touch the wires together (be sure the key is "ON"). If not, you need to determine which side of the switch the problem is on. First check with a test light, you should have power at one of the two wires. Second, supply power to the wires one at a time, see if the lights come on (this is easy, touch them to the battery cable post on the starter. The complete circuit is: the back-up lights get power from the same fuse as the brake lights, the wire branches off at the brake light switch. It then goes into the engine compartment relay board at pin 14/3, comes out at 12/2 and goes to the switch. It returns to the board at 12/4 and leaves for the lights at 14/4. For the back-up lights the relay board is a junction between the front and rear harness. Check for a switch problem after you get the lights to work bridging the wires at the switch.

JFinnell

Thanks for the help!
Does the car need to be started, or would it suffice to have the power on, e.g. turn the ignition to where the fuel pump and radio function?
Now that I know how the circiut is designed, I should have more success with my multimeter. To be honest, the diagrams in Haynes were not near as clear as your explanation.
I will reply with the results for the sake of posterity.

Ed Morrow

Key on, engine not running will supply power to the switch.

JFinnell

It took a bit of back and forth from the relay board, to the backup switch, to the backup lights. The backup switch was found to be faulty, but this did not completely solve the problem. I also had to take a razorblade to spread the pins on the relay board.

I would suggest that everyone carefully use a razorblade to spread the four-pronged pins on the relay board, fuse box, headlight motors, etc... I saved a bundle on headlight motors by spreading the pins for the headlight relays. Be sure to disconnect the battery and don't break the pins. I simply slide the razorblade between the prongs (twice for each pin). I do not move the razorblade from side to side as this was not necessary.

Thanks Again!!