My Backup Lights are Intermittant and Dim (74 911)
 

Howdy! My 74 911 has B/U lights that are Intermittent and when they do work they are dimmer than normal. IMO, a poor Ground is indicated, but I'm not sure where to look for a common ground.

Need some advice on locations of common grounds, please. Is it possible the wires on the B/U Switch are covered with enough oil that their connection is intermittent?

TIA!
Larry Turner
Chester, Va
74 911 - Red

The only grounds for the reverse lights are at the same point as all of the other lamps in the taillights.
So, they would all act that way.
More likely a bad switch or connection at the switch or at the 14 pin connector.
Yes, the wires to the switch can get really oily.

Basic path for reverse light power.
Front fuse panel to 14 pin connector, to reverse switch.
Back from switch to 14 pin connector, splits to both taillights, goes through bulb to ground.

I’ve had a few switches over the years that showed high resistance with ohmmeter causing intermittent operation.

Thanks for the comments guys! The BU lights are 3rd in behind the starter and trans shaft seal. Hopefully I'll finish the 1st 2 things quickly so I can fix the BU lights and get it inspected!

Thx agn,
LarryT

The reverse light wiring is often unnecessarily but intentionally cut by people when taking the engine/trans out of the car. The reason they do this is because they don't realize that the wires have bullet terminals on them which simply pull out of the switch body. So be sure to check for crappy wire repair. If you need to repair it, it's easy to salvage the bullets by heating them up with a torch or soldering iron and releasing the crappy wire. Then you can of course solder new wire into the bullets and re-splice with new wire.

Also test the switch manually by simply sticking something in the switch hole and check for continuity with an ohmmeter. You may just have a faulty switch since it's most likely 47-ish yeas old? Yikes that sounds old in car parts age and coincidentally as old as I am personally! Yikes again.......

The switch is activated by a pin in the transmission, which contacts a roll pin that's inserted into the 5th-reverse shift fork rod. It's sort of comical how crude it's activated. So be sure to check the pin itself along with the switch. The pin tends to wear out over time and, if you can believe it, it gets shorter which reduce its effectiveness in activating the switch. So you may end up do-it-yourself fabricating a new activation pin and the trick is to use a drill bit

http://forums.pelicanparts.com/porsche-911-technical-forum/422046-reverse-light-switch-woes.html