Camry 99 Back Up Lights Do Not Work When Head Lights are Turned On

Try here:Download| Toyota Camry Gen4 (1997-2001) Electrical Wiring Diagrams ...

I guess other lights at the rear of the car work, like tail lights and brake lights, right?

They are grounded also, and you should be able to trace a wire from those lights to a part of the body where they are grounded.

Then you can test for voltage on the back up lights with one terminal of your meter connected to the ground you located above. (I'm guessing its actually the same place for the back up lights as well.)

If the engine needs to be running when you test the back up lights, be careful--take appropriate precautions.

The back up light might pass via your central locking / alarm system (to flash whenever you lock or unlock) and may pass through the computer as well.

on a multi purpose item a fault in one system might disable the other.

The Camry also uses fuse-able links.

The limit switch / sensor at the gear lever / gearbox may be out of order.

Get a copy of the wiring diagram and trace what is working and note the place where it stops.

The relay operating the light might be stuck - cycle the switch and listen for the click.

Some of the relays / terminal boxes is situated behind the dashboard.

From your problem description, my understanding is that the backup lights work just fine as long as the headlights are off but the instant you turn them on the backup lights go out. And if you turn the headlights off, the backup lights pop back on (assuming you're in reverse).

I'm not sure if this is the actual problem or a symptom of a problem somewhere else. Getting the schematic is an excellent first step, though. Hendrik's idea about the source may be right on; some car makers use a 'body control module' which controls a whole lot of things that used to be directly controlled by switches, etc. Sort of a fly-by-wire approach. If it's the BCM that's more than likely a dealership fix.

There are a whole lot of questions that could be asked. Here's a few that may help narrow this down. Are there any other symptoms? Any codes being thrown by the onboard computer? Has anyone worked on the car or changed anything recently? Could it somehow be weather related, or maybe only happens after the car's been driven enough to warm up? Does it matter if you use high beams vs. low beams vs. daylight driving lights (if your car has these)? What happens if you turn on the headlights first, THEN move the gear to reverse? Are there any modifications to any parts of the lighting system? Is there a trailer towing harness involved?

If you can provide information for some of these (and any others you can think of), it might be just what someone needs to send you in the right direction.

Good luck!

Spook