back up lights

Yes. You need to get hold of a multimeter and check out what voltages are available at the bulb holders with the ignition turned on and reverse gear engaged.

I'm not familiar with your particular model, but I would expect that the outer contact of the bulb holders should be connected to chassis (check with meter set to measure resistance [should read 0 ohms]). The centre contacts should be fed with +12V, from a switch mounted on the gearbox/gear linkage.

If the resistance between holder and chassis is greater than a couple of ohms, you need to sort that out. If 12V isn't present on the centre contact, then you'll need to locate the switch on the gearbox and ensure that it is correctly located, that there is a 12V feed to it, and that the the 12V reaches the other switch contact when reverse gear is selected.

The results of these tests should narrow down the areas for further investigation.

Just a thought - I know that some Audis have the reversing lights mounted on the boot lid, and a common point of failure is the wiring between the main body and the boot lid.

Scotty C, What Peter said, but also: it could be that the switch has broken - check it (most probably mounted on the transmission, not sure with the 90) to make sure it's operating. Cheers! Steve Sears

1987 Audi 5kTQ 1980 Audi 5k 1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply)

'bellfamily')