Courtesy Light

[mfarmitage]

Having decided to try and fix everything thats wrong with my little 1986 740 i have now ordered a new-old courtesy light, the previous owner had installed a battery light which makes me think the old light lost power.

I just checked and the green/red wire has 12v but the brown wire never gets voltage. I have looked at the wiring diagram and it looks like the green/red is the door open light control? Why would that be always hot? Any idea why the brown wire doesn't have voltage? The fuses are all good.

I opened the 2 doors and still no voltage to the brown wire.

My conclusion is, faulty door switch is making the red/green always on or... does the light go off when the engine is started?

or i have completely misread the wiring diagram

Help!

Thanks in advance

Michael

[Forrest]

Are you sure the switches don’t complete the circuit to ground via the vehicle bodywork? That’s how they work on 940s and is a fairly common approach. This would mean the incoming live to the light would be permanent and the brown wire should connect to ground when a door is open. What often happens is the connection to the vehicle bodywork corrodes and/or the contacts inside the switch deteriorate. It is possible to clean everything up and make the switches work again but I’ve found it more reliable on my 940 just to buy new switches.

[Ian21401]

What Forrest said.
The courtesy light in my 940 works fine on three of the doors but the offside passenger door switch is rather temperamental. I removed it expecting it to have only one wire connected and to earth through the switch screwed to the B post. It had two wires connected, green/red and blue/black. The action of the switch connected these two wires so it appears that the earth is somewhere else and not through the switch attachment to the B post. I checked the connections and cleaned the switch contacts which seems to have improved matters somewhat but it is still a little temperamental.

[mfarmitage]

more testing tomorrow i think . that kind of makes sense... thanks

while im here does anyone know if the 740 heating controls should have lights?

[MiniNinjaRob]

Originally Posted by Ian21401

What Forrest said.
The courtesy light in my 940 works fine on three of the doors but the offside passenger door switch is rather temperamental. I removed it expecting it to have only one wire connected and to earth through the switch screwed to the B post. It had two wires connected, green/red and blue/black. The action of the switch connected these two wires so it appears that the earth is somewhere else and not through the switch attachment to the B post. I checked the connections and cleaned the switch contacts which seems to have improved matters somewhat but it is still a little temperamental.

It is earthed through the post. I tested a switch of mine that was causing an issue - the interior light was always on - and a test seemed ok. However swapping it with another cured the issue. When the door closes I think it disconnects across the wires but connects to the Earth.
I ordered a new switch off eBay for a few pounds and it all works fine now. I think the contacts inside just wear out eventually.
I may be wrong but that’s how it worked for me.

[Forrest]

I’ve always assumed the two wires at the door switch on the 940 were one for the light and one for the alarm, both earthed through the door pillar; but I’ve never investigated this fully.

[Laird Scooby]

Originally Posted by Forrest

I’ve always assumed the two wires at the door switch on the 940 were one for the light and one for the alarm, both earthed through the door pillar; but I’ve never investigated this fully.

You've got a delay on your interior light haven't you? One wire goes direct to the interior light to turn it on by completing the circuit to earth. The other triggers the delay unit built in to the light which keeps the light on for up to about 30s after the door is closed.

[Laird Scooby]

Originally Posted by mfarmitage

Having decided to try and fix everything thats wrong with my little 1986 740 i have now ordered a new-old courtesy light, the previous owner had installed a battery light which makes me think the old light lost power.

I just checked and the green/red wire has 12v but the brown wire never gets voltage. I have looked at the wiring diagram and it looks like the green/red is the door open light control? Why would that be always hot? Any idea why the brown wire doesn't have voltage? The fuses are all good.

I opened the 2 doors and still no voltage to the brown wire.

My conclusion is, faulty door switch is making the red/green always on or... does the light go off when the engine is started?

or i have completely misread the wiring diagram

Help!

Thanks in advance

Michael

The green/red wire is your +12V permanent feed to the interior lights. Are the bulbs ok and the switches on the light in the on position??? Middle position is OFF!!!

Start on the drivers pillar switch, remove the screw holding it to the pillar and pull it out - clean the pillar where the screw fits with emery cloth, likewise the back of the switch where it meets the pillar.
Also remove the wire connectors from the switch and clean the tabs.

Reassemble it all with some silicone grease behind the switch and on the screw, if everything is ok you might see a tiny splash of current sparking as you do the screw up and the light comes on

Repeat for the other 3 doors.

Originally Posted by mfarmitage

more testing tomorrow i think . that kind of makes sense... thanks

while im here does anyone know if the 740 heating controls should have lights?

Yes, they should. Looks quite effective as they are coloured bars on the sliders if memory serves.

[MiniNinjaRob]

Originally Posted by Laird Scooby

The green/red wire is your +12V permanent feed to the interior lights. Are the bulbs ok and the switches on the light in the on position??? Middle position is OFF!!!

Start on the drivers pillar switch, remove the screw holding it to the pillar and pull it out - clean the pillar where the screw fits with emery cloth, likewise the back of the switch where it meets the pillar.
Also remove the wire connectors from the switch and clean the tabs.

Reassemble it all with some silicone grease behind the switch and on the screw, if everything is ok you might see a tiny splash of current sparking as you do the screw up and the light comes on

Repeat for the other 3 doors.

Didn’t work for me. It all appeared to work ok when tested away from car but for some reason not when connected. New switch sorted it.

[mfarmitage]

Originally Posted by Laird Scooby

The green/red wire is your +12V permanent feed to the interior lights. Are the bulbs ok and the switches on the light in the on position??? Middle position is OFF!!!

I don't have the new light yet, I was just trying to figure out why the previous owner went battery before the switch arrives but thanks now i know it seems to be getting power ok.

on the drivers pillar switch, remove the screw holding it to the pillar and pull it out - clean the pillar where the screw fits with emery cloth, likewise the back of the switch where it meets the pillar.
Also remove the wire connectors from the switch and clean the tabs.

great, i'll give it a go.

Yes, they should. Looks quite effective as they are coloured bars on the sliders if memory serves.

looks like i need to fix the bulb then as i have no light there atm.