Got a good one... light/electrical woes! Help!!

[aaron7]

Subject is a 1989 Corolla SR5.

The lights don't work, except the headlights. No dash lights, no backup lights, no plate lights, no front or rear parking lights, and no side marker lights. Oh, and the dome light only works with the doors, not in the ON position.

Now, this is with the headlight switch on or off. I tried the dimmer switch too, but got nothing.

Here's the freaky part... all the fuses are good.

Here's the freakier part... ALL the lights above except the reverse lights and the dome light come on when I press the brake pedal, regardless of the headlight swtch being on or not!!

What the hell is going on?? Is it posessed??

[emiliorescigno]

Don't hold me to this, but one set of bulbs may be the incorrect wattage. This exact thing happened to my mom's 1997 Mercury Villager when some foolish mechanic put in the wrong brake light bulbs, as soon as the bulbs were replaced the problem went away.

[aaron7]

What the hell right? Can't hurt to check them!

If I take them out, the rest of the lights should work, right?

[RedAE102]

My educated guess: a combination of things... a bad taillight relay and a bad brake light bulb... the latter being that one of the wires inside the bulb has likely come loose and shorted to the taillight lead. The relay may be bad, or there may be another wiring fault (possibly even a bad switch or ground).

The dome light not working in the ON position automatically indicates a bad switch or ground in the light, as the ON and DOOR positions share the same constant-on positive lead.

[aaron7]

Originally Posted by RedAE102

My educated guess: a combination of things... a bad taillight relay and a bad brake light bulb... the latter being that one of the wires inside the bulb has likely come loose and shorted to the taillight lead. The relay may be bad, or there may be another wiring fault (possibly even a bad switch or ground).

The dome light not working in the ON position automatically indicates a bad switch or ground in the light, as the ON and DOOR positions share the same constant-on positive lead.

Ok, well I unplugged the taillight bulb housing connectors and the lights still didn't come on. I also unplugged the side markers in the rear to no avail. I did also unplug the reverse lights. No go.

Where is this relay?

[Williams]

try jumping your ground source to a good known ground. Many problems turn out to be a bad ground. Just find a spot in the harness somewhere that there should be a good ground, and jump to a known good ground ....I've sorted many electrical problems this way.

[RedAE102]

Originally Posted by aaron7

Ok, well I unplugged the taillight bulb housing connectors and the lights still didn't come on. I also unplugged the side markers in the rear to no avail. I did also unplug the reverse lights. No go.

Where is this relay?

The bad bulb part is the most likely cause for the parking lights coming on when the brake lights do... not the cause of the taillights not functioning otherwise. The taillight relay can be found in the junction/fuse block in the driver's side kick panel.

[aaron7]

Had the problem diagnosed and fixed by a local emissions/wire guy... turns out either my aftermarket sunroof or the windshield leaked (or still does) and corroded the fuse box, and wasted the taillight relay.

So, $313 later (the relay alone was $50 I guess), I'm off and running! Wait, no, I'm not. I need a radiator still. AHHHHHHHHHHHHHHHHHHHH

[aaron7]

Ok, I noticed that last night the lights all still came on with the brake pedal. So the corrosion problem was just why the lights on the switch didn't work.

So I took it back to the guy. 10 min later he showed me a bulb in the taillights that was the wrong kind (was supposed to be the kind with 2 connectors, only had the one) and that was it! Now my problem is totally fixed.