Back-up Lights

[Boaf32]

Hello 928ers,

86 1/2 928:

928ers,

I have been tracking down a back-up light problem. Back-up lights only go on when the parking lights are on.

Determined the relay XXII is OK. Performed these steps from Walley:

1) Pull Relay XXII. Check for 12 vdc at terminal 30 in the socket. If no power, check Fuse #12.
I recorded 2vdc ignition off; 10.9vdc ignition on

2) Jump 12 vdc to terminal 87 in the socket. Reverse lamps should light. If not, check bulbs and wiring.

Did this and the lights came on..
3) If you have power at terminal 30, and the lamps light when you apply power to terminal 87; then turn ignition on and put shifter in R. Check for 12 vdc on terminal 86 in the socket. If you have 12 vdc, replace the relay.
Did this and recorded 10.9v

At the light plugs in the rear of the car, ignition on and car in reverse:
(4vdc with parking lights off, 10,9 vdc Park lights on)

S00ooo, that background, what would cause me to only have 4vdc at the rear (with no parking lights on). My grounds are clean and I jumped a temporary ground as well, no luck. Suggestions about replacing the bulb sockets?

The other question, does the combination relay (XXIII / XXIV) feed power in any way to the back-up lights? Schematics seem to indicate so.

Thanks.

Bob

[Danglerb]

2vdc, 10.9vdc, those mean you have a poor connection and/or a short. I would try tracing both of those voltages back toward the battery until you find the segment that is bad, and that needs connections cleaned or wires replaced.

*** Holiday weekend *** it may take a few days for good answers to show up.

[ferrispa]

I think that I had a similar problem. I had to make a few small cuts in the surface of the harness to locate the appropiate cable and then stab the plastic with a pin to check the continuity with an ohmeter at different intervals. Finally I found that the copper cable was broken although the plastic surface was intact. In this section the cable offered quite high resistance but still some continuity due to the internal oxidation of the wire which had been destroyed by the damp.
Hope this is of help. Good luck!

[Boaf32]

Gents,

Thanks, I found out that Pin 86 in the Relay that goes to wiring harness U-21 only gives .4v at best. I actually did splice the sheathing and found the blue wire that feeds the rear back-up lights. That too has the low voltage.

928 Specialist said to pull the rear bumber and pull the sockets to check for bad connections there. Sooo still going. great suggestions. The only drag now...I shorted something out and the reverse lights won't even work with the head lights on so another exciting track

Any other suggestions? I know that the reverse shifter was very loose and maybe the reverse switch (where ever the heck it is) may be loose too.

Bob

[rhjames]

Bob-

my Dad's '79 has a similar issue with the rear taillights.

the right rear has not been working, the relays/fuses were checked and found to be good, the wiring to the housing is good, but the bulb only lit for a while and now is not working again. New bulbs haven't worked, so it looks like the housing is bad-----again.

this makes the third housing he's tried.

I hate to see him put a brand new one in ($$$$) but that may be where he's headed.







--Russ

[Boaf32]

Thanks Russ, all,

I will keep working on it over the winter and follow-up with what the solution was (if I get it find it!) Think positive

Bob:

[Alan in AZ]

If you jump 12v to the 87 relay terminal and the lights light - all your power wiring from the relay and rear lights are OK. So its either the relay - swap with the horn, or its the feed to the relay coil from the selector switch.

Put a small 12v bulb ~ 1-2w between relay pins 85 & 86 - does it illuminate when you select reverse? if no its the selector switch/feed or relay coil ground that is at fault.

There is no relationship between marker lights and reversing lights - that there does seems to be - suggests a grounding issue somewhere... check the grounds at the CE panel (2 locations behind/above the panel - are they clean/tight)

Alan

[Boaf32]

Hello All,

Thanks for great ideas and suggestions. Wally from 928 was great! Turns out the issue was not ground related. A supply wire from the CE Panel that feeds the dashboard gear indicator was broken. This supply feeds a total of 6 other wires. The one that fed B6 (the gear indicator) in the dash pod also feeds the neutral safety switch on the transmission. That switch sends the signal for the back-up relay to close. There is the live circuit.

So after removing the bumper to take out the lights, removal of the CE panel and countless "oh Craps", the issue is finally solved. Yeeha!!! But... it's winter and there's snow on the ground