I found a Previa forum and posted there but thought I'd try my luck here since the rescources are better. Toyota lists Previas as trucks so technically... <img src="/forums/images/graemlins/pfft.gif" alt="" />

When I step on the brake, other functions are lost. The parking lights go out and brake lights nevvr come on. The dash lights, clock, radio, heater fan and windows were lost too. Since I had a fan switch meltown in the past, and it supplies heater control panel lighting, I put a new one in. The old one had one burnt pin but wasn't completely melted down like the first switch I did years ago.

Sometimes when turning on the parking lights the tail light relay buzzes. Sometime they are just slow to come on. Once they do glow you can turn them on 3-4 times in a row and its ok. Usually once they are on and you step on the brake pedal, then the dash, tail and brake lights go out (and all the other stuff I listed above). The headlights always work.

Things I've done so far:

All exterior lamps have been taken apart, inspected and/or new bulbs put in. all looked good.

New battery (it was long overdue anyway)

New fan control switch (its a Previa thang)

Brake pedal switch has been disconnected. Problem persists

Brake switch bypassed and activated by jumper wire....same problem persists

Taillight relay has been swapped with others that were good

Voltage at battery (when engine off) 12.35v and 11.30 at the tail light socket (parking light pin). 8.5v when the brake light switch is activated and then meter goes goofy while the tail light relay is buzzing/chattering.

Now off to Rooster's. I shall return 3 drafts and 15 hot wings from now <img src="/forums/images/graemlins/cheers.gif" alt="" />

Has any after market type of electronics been installed recently (radio, CD changer, etc.) or even a trailer wiring adapter? If so, try disconnecting that and see if the problem persists. I had some similar type of issues with my '85 4Runner after swapping out a radio and used the PO's hacked up wiring to hook it up.

Otherwise, sounds like a ground issue, Toyota uses a lot of switch ground circuits for lights (a ground connection makes the light turn on). All fine an dandy until you lose a ground connection some place and then you'll find things like the parking/running lights find ground through the brake lamp filament. And that is fine and dandy until you apply the brakes (and that kills the ground path) and now all the lights go off. The fact that you see a voltage change at the parking lamp pin when the brakes are applied says this may be the case.

I agree with Rodger...
look for the hacked trailer wiring. those blue clip on things.
remove it and fill the slice in with silicone.
you have a short some where, don't mess around you will set your truck on fire. A wiring fire is ugly. it keeps burning untill you get the battery disconnected and the fire put out.

No aftermarket. Completely unmolested 16 year old Toyota.

With the mention of grounding issue I may have to look at battery cable, the fact I loose almost all functions other than ignition its not just a local light bulb ground I'm looking for.

Probably need to check all the ground connections, not just the battery negative cable. Usually a few in the engine bay and one or more inside the cabin. Don't just look at them, I found one in my 4Runner that would cause the cruise control to drop out any time I hit a good bump on the road. Found the ground connection and removed all the wires running to it, wire brushed them all clean as well as sanding the sheet metal under the ground screw and that problem was gone. Everything looked OK at the initial visual inspection.

Thanks Roger. First thing in a.m.

Trying to get thing college ready for my daughter. after all it is a dorm room on wheels!

battery cables removed and thouroughly cleaned (didnt look bad to begin with). I even istalled another ground wire from battery to firewall. Still having the same problems.

Grrrr

Might try digging out a volt meter and start probing voltages at various points. Test with all the bulbs removed and compare the voltages with say one side of bulbs back in. See if you can track down any circuits that are working normally and those that are not and work back to where the problem cause is.

Check the rear tail lights for water in the socket or the wiring harness are cracked under the bed. Had the same problem with my 86.

12.35 is kinda low, I predict a new battery will be needed next winter.

11.30 is a lot of voltage drop. I agree with the folks saying check *all* grounds, also unplug & check any connectors you can get to.

Pay extra attention to the circuits feeding the tail light relay, if it's buzzing, it isn't getting enough current to pull the switch fully.

Dave