Ok, here is a conundrum.

Mk 2 Mondeo 1.8 Verona petrol, manual.

Both reverse lights are inop' . Several of the rear light bulbs where out when I first got car and I replaced these.

But the reverse lights still don't work. I've swapped out the bulbs for known good ones. I have put a meter on the contacts and I am getting 12v and ground.

Any ideas ?  🤔

Strange if you've got voltage there, have you switched it in and out of reverse while the meters attached to see what it's doing.

Doesn't sound like it in this case but the last time my reverse lights didn't work albeit it was on my focus the reverse switch had jammed and bent the selector arm. 

Not sure about your model but on quite a number of cars of that age the reverse light lamps are supplied a constant positive 12V once the ignition is on. Then when the car is put in to reverse the gearbox makes the earth (negative) connection.

With the ignition on put your meter between the centre contact of the lamp holder and a good known earth point. If it reads 12V with the car NOT in reverse then it should get the negative via the gearbox switch.

On my mk1 focus the reverse light did not work even though voltmeter on bulb holder appeared fine.   I twiddled the connector on the gearbox switch and then it worked properly. It seems it had a poor connection which allowed voltage for voltmeter to see but would fail to supply enough when under load (1.75 Amps for one 21watt bulb)

Thanks I will check out your suggestions when weather and time allow.

Whilst you are checking the reverse switch on the gearbox, check for any oil fouling as sometimes that can cause problems. Had a similar problem once so checked there was no actual oil leak (there wasn't), then just cleaned the switch with contact cleaner and it was all ok after that.

On 10/13/2021 at 1:52 PM, erictcleric said:

Whilst you are checking the reverse switch on the gearbox, check for any oil fouling as sometimes that can cause problems. Had a similar problem once so checked there was no actual oil leak (there wasn't), then just cleaned the switch with contact cleaner and it was all ok after that.

Well managed to get out and get under. As I climbed underneath I recalled a similar problem I'd had with a Mk3 Cortina. ☺️

Then realised the gearbox does not live underneath anymore ! The switch was indeed covered in oil and grime so cleaned area and connection. I disconnected and bridged, proving circuit ok. I removed the switch but no continuity with ball depressed or not. I tried to dismantle but to no avail. I then sprayed with WD whilst depressing ball on switch, checked with meter. Yay, it worked. Refitted, Boo, it doesn't work ?

Any adjustment in the switch or on gearbox side ?

Sorted folks. Cleaned all the grease and grime from the area. Removed the plastic cover to check mechanism was working ok.

Made sure the bolts holding the plate on top of 'box where tight. Tried separating the two parts of switch which wasn't happening. So held the bolt part and tapped in the plastic connector bit. refitted, nice n tight. And behold I have working reverse lights !