Reverse lights stopped working - Checked switch, bulbs, fuse

[Ro3345]

I know the switch is the common culprit but mine seems to be switching ok (there is continuity when in reverse).

I tried shorting the 2 pins on the connector, nothing.

Both bulbs are ok.

I checked Fuse 10, it's ok.

What else do I need to check?

[Topblag]

Swap out the switch with a known working one and if no lights, start tracing cables.

[Brianmoooore]

Pull the plug and socket at the base of the gear lever apart (under the gator).
Turn the ignition on and connect a 12 volt bulb between the green/white wire and a good body earth to check if power is present.
Connect 12 volts directly to the blue/white wire and see if the reverse lights light up.

[Ro3345]

Pull the plug and socket at the base of the gear lever apart (under the gator).
Turn the ignition on and connect a 12 volt bulb between the green/white wire and a good body earth to check if power is present.
Connect 12 volts directly to the blue/white wire and see if the reverse lights light up.

Thanks, I will try that.
I just removed the seats and front carpet so perhaps i damaged a wire or connector somewhere.

[Connieblau]

There’s a plastic, black box called a lampenkontrollgerat (yes really) or better still a ”˜light lamp control modular relay’
1. 375. 909 which apparently organises the dash Lights out message for reversing lights etc. I have a rhd facelift convertible and mine is near-side just in front of where the wiring loom, antenna cable etc disappear into the boot. I did read somewhere they’re sometimes inside the boot. Black plastic box 100mm x 60mm x 30 deep with one white clip-in connector with 8 cables, one black connector with another 7. Nothing comes out the other side. Mine wasn’t kaput, but it wouldn’t be awkward to replace.

[Brianmoooore]

There’s a plastic, black box called a lampenkontrollgerat (yes really) or better still a ”˜light lamp control modular relay’
1. 375. 909 which apparently organises the dash Lights out message for reversing lights etc. I have a rhd facelift convertible and mine is near-side just in front of where the wiring loom, antenna cable etc disappear into the boot. I did read somewhere they’re sometimes inside the boot. Black plastic box 100mm x 60mm x 30 deep with one white clip-in connector with 8 cables, one black connector with another 7. Nothing comes out the other side. Mine wasn’t kaput, but it wouldn’t be awkward to replace.

This is true, but unfortunately it doesn't monitor the reverse lights, and the reverse light wiring doesn't pass through it.
The light module only monitors the obligatory lamps (tail, brake and number plate) with the exception of the indicators, which have their own failure warning system.

[magpie]

i think he's un plugged the white block connector at the gear selector while removing the carpet .

[Ro3345]

i think he's un plugged the white block connector at the gear selector while removing the carpet .

No the connector wasn't unplugged. I did think to at least check that before asking the forum.

I thought maybe I had disturbed something elsewhere but that doesnt seem to be the case.

Switch works fine but not getting 12v to the connector.

[Brianmoooore]

Switch works fine but not getting 12v to the connector.

You checked between the green/white wire at the plug near the base of the gear lever and earth, and there was no voltage with the ignition on, as I described in my first post?

[Ro3345]

Switch works fine but not getting 12v to the connector.

You checked between the green/white wire at the plug near the base of the gear lever and earth, and there was no voltage with the ignition on, as I described in my first post?

Correct. Got 12v up at the fuse, but not getting anything at the green/white wire.

[Brianmoooore]

There should be three green/white wires connected to the underside of fuse 10.
One of these is just a short loop inside the fusebox to the coil of relay K7 , while the other two travel down inside the duct under the fusebox, and emerge as part of the loom behind the glovebox.
One of the wires then goes to a joint, where all the items fed from fuse 10 are individually fed from, except the reverse lights. These are fed by the other wire which goes all the way to the socket at the base of the gear lever with no joints whatsoever.
The route of the wire is down in the corner behind the LH speaker panel, back along the sill, across to the middle in front of the floor crossmember, then up onto the tunnel. The wire shares this part of the loom with the handbrake switch and rear ashtray light wires.
In short, if power is at the fusebox, but not at the socket by the gear lever, there is either a duff connection at one end of the wire, or it is broken somewhere along the way.

[Ro3345]

Thanks. Great info.

I'll look under the fuse box so.

[Ro3345]

Any tips for accessing the wiring in the fuse box?
There is 2 screws and an small allen head bolt on top. I removed the screws and tried backing off the allen head bolt slightly. but it still seems to be held down. I dont want to try pulling or prying anything for fear of damaging a solder joint or something.

[Brianmoooore]

DON'T TOUCH THE ALLEN BOLT! It secures the main 12 volt feed from the battery.
Fusebox deck is held down by three small self tapping screws - one outside, and obvious, one inside, and obvious, and one hidden under one of the black relays.
Pull the deck carefully up. Movement will be limited by all the wires connected to it, but by applying a sensible amount of force and possibly cutting the odd cable tie, you should be able to get it up far enough to see what's what. The only thing to be careful of (other than sorting the allen bolt if you moved it), is to ensure that the six(?) pin plug is pushed fully in place when you refit.

[Ro3345]

DON'T TOUCH THE ALLEN BOLT! ...

Luckily I copped it wasn't holding the deck down before I backed it off fully.

Anyway, issue is solved.

My car actually has a green/yellow wire to the reverse switch.
I thought nothing of this until i saw the green/white wires from fuse 10.
The green/yellow wire was coming from fuse 9 which turned out to be blown.
I thought fuse 9 was only used on auto cars.
There was no sign of any re-wiring by a PO so;
Is there a different fuse box diagram for 1984 318i?

[Brianmoooore]

Just looked up an '84 wiring diagram for a 318i, and it shows F10 for the reverse lights with a green/white wire, exactly the same as the last E30 produced in '94. F9 was listed as "idle speed control".
I then had a lightbulb moment, and decided to dial up the '83 diagram as well, and sure enough, F9 is listed as "idle speed control AND back up lights"!
F9 , as you say, is used for auto transmission on later cars.
There's always something new to learn!