Real weird electical problem - Reverse lights - low power -

[Rory]

HELP! Im just spent hours trying to get my reverse lights working for my MOT next week with no joy. Ive tried several known good light bulbs. The problem is that there is 12v (tested with multi meter) coming down the wires but as soon as you connect a light bulb (even direct to the wires) the power dissapears. It seems to just dissapear when you try and use it! All my other bulbs inlcuding headlights light up nicely however there only appears to be enough power coming from the reverse feed to light a small indicator bulb! Its really doing my head in. Can anyone shed some light? I think if i cant get it going im going to temporary wire a switch and new feed inside the car to light up the reverse lights. This should get it through its MOT.

[chunkymonkey909]

My guess is a poor ground connection. Check the resistance from the bulb ground connector to the chassis it should idealy be 0 but if its more that 1 or 2 ohms then that could be the prob.

[Rory]

My guess is a poor ground connection. Check the resistance from the bulb ground connector to the chassis it should idealy be 0 but if its more that 1 or 2 ohms then that could be the prob.

Thanks for the reply but ive already checked the earth already. I tried using the earth from another circuit and also tried an earth from a bare metal bolt. Neither worked.

Rory

[Terry]

I thought you didnt need reverse lights for the MOT??

[paul port]

You clearly have a multimeter, so here is a structured fault finding procedure...

1. Select reverse, put in the correct bulb. measure the voltage from a GOOD chassis earth bolt to both wires going to the reverse light.
If any one of them reads 12v, then the fault IS either the earth for that lamp, or the bulb socket it's self.

Assuming both read close to 0v:
2. Find the reverse light switch (Gearbox) and bridge it out
Does the light come on OK?
Yes - replace switch
No - continue

3. Attach wires to a representative reverse light bulb. connect one wire to a GOOD chassis earth bolt, poke the other wire into the two socket holes on the chassis loom that plugs into the reverse switch.
Bulb lights - the fault is in the wire from switch to reverse bulb socket
Bulb does not light - fault is in the wire from the ECU-IG fuse and the reverse light switch.

paul

[Rory]

Thanks for the reply Paul. Ive just got back from hols. My car passed its MOT without reverse lights so its no longer an urgent job. Ill check it out when ive got a bit more time on my hands.

Rory