Hi,

I have a 911SC, with a 993 engine installed in it, but using the standard 911SC gearbox.

The problem is, the reversing lights are staying on all the time I am driving (or anytime the ignition is on).

Whats the likely problem?

Is this a common fault?

Just looking for some answers before I jack it up and get under it.

 

Don't know a whole lot, however it appears the back-up light switch is stuck on. I don't have my manual here at work, however I believe the switch is located on the tranny.

Maybe someone with more insight will jump in.

Good luck!

 

On engine swaps the problem is usually in the wiring (reverse switches rarely fail in the 'on' position). It sounds like the wires at the switch are touching inside the rubber switch cover. The switch is located on the nose of the transmission. You can access it without removing the front trans mount (using a good needle-nosed plier), but it's tricky. Work in a well-lighted area and if you jack up the car use jack stands and leave the jack under the car for extra protection!
Pete

 

Sounds like it could be a crossed or pinched wire, thus completing the circuit. I am not sure if it has an actual switch that is adjustable, if so it needs adjustment. Either could be the problem. Need to trace the wire from the switch and see what you find. Good luck.

 

to help put the above in context, it might be useful to know how the circuit works. As I recall, there is 12V to the lights all the time, and the ground is switched by the B-up switch in the trans. So, it could be the switch itself, or the wire could be chafed and shorted to ground somewhere. easiest first step? Pu;ll the wire off the switch and if the lights go off, it is the switch if not trace the wire back til you find the short.

 

Dave: Close, but no cigar! Switched 12V is supplied to the back up switch on the trans, when R is engaged the switch is closed completing the circuit to the lamps. The wires at the switch have hold-overs from the 356, bullet connectors. When they are treated badly the wire inside the connector can break, if that happens, or if the connector isn't seated properly, the two wires can touch inside their rubber boot. That's why the reverse lights are on with ignition or when the car is running. Of course, after an engine swap all bets are off regarding electricals!
Pete

 

I have an '85' Carrera Cabriolet (original transmission and engine) with a similar but opposite problem as above. Everytime I put the transmission into reverse, I blow a fuse and of course no reverse light or turn signals. Anythoughts as to how to trouble shoot this?

 

85: The hot wire is probably broken/frayed, and is touching the switch. Use the above post that tells how to access the switch, or in the meantime go to your fusebox and remove the power source for the back up switch (leave the power wire for the T/S system intact). That will allow you to have turn signals until you can track down the short. There is a possibility that you might have a harness problem, the wires come from the top of the engine, but definitely check the connections at the switch first!
Pete

 

85 cab.

I think the hot wire to your switch is probably okay as it has a constant 12v while the ignition is on and you don't have a problem. The problem is the wiring from the "load side of the switch. If is is nothing obvious with the switch here is the best way to troubleshoot it .

1. remove the fuse for the back up lights. put a multimeter set on ohms ( resistance ) on the cold side of the fuse connector and a good ground point. When you put it in reverse the resistance value will drop to 0 ohms ( short). start unplugging things until the resistance increases. I would pop the bulbs out and check the socket bases if the switch looked okay.

 

ice: DUH! I'm a dummy! I meant to say the switched wire, not the "hot" wire. I think that I fell asleep just before writing that... Good post!
Pete

 

Hey .. I got one " Mr Zimmermann" didn't ahem thank you, thank you very much :-).. but I still want to know why you are the only one who gets " Mr. " .. no respect I tell ya !

 

All right, mister, check the hold down thread! LOL!
Pete

 

Okay I checked the thread you win ... what a weak post for my 1000th... and I was anticipating a much better one .... anyway it has been a blast and when I noticed I was aproaching 1000 I was totally shocked .. here's one to you guys

 

Was the doner a tip or manual? The reverse light switch activation is the main difference in the wiring harness between the 2.

 

These messages help a lot. I have my Bentleys Manual and wonder how accessable the switch is without dropping the transmission. Clearly the Cab has to be lifted on jack stands. Is it possibly a faulty switch requiring replacement or are the switchs generally solid.