problem with tail lights

[t_cel_t]

ok my bro has a 90 camry le and he had a problem with the battery and want to the store bought another one and hooked it up and found out after the shower of sparks that they had given him the wrong battery (terminals were backwards). well he blew out about every fuse and now his tailinghts will not work. the bake lights, side markers, turns, even the place lights work but the tails wont.
i tried running a wire from the side markers and from the plate lights but the lights are at the full brightness, like they are running at 12v.

how do they get that dim light from them, did toyota have something that cuts the power going to the taillight bulbs down to 9v or something?

[marc780]

Use a volt ohmmeter or test light to test for voltage at the fuse. Are the taillights AND brake lights out too? (They are two circuits.) How about the turn signals? (Another circuit.) If NONE of these work at all, then you have to ask what do they all have in common? Ans - ignition switch and fuse box. If the rest of the car works then its a safe bet the ignition switch is not at fault. So maybe a contact got fried in the fuse box somehow.

Trace the wiring with a vom or test light until you find the point where no power is. Its possible a wire or two may have been fried by the backwards battery hookup. Test for power into the fuse and out of it, if theres no power going into it then you may want to find a decent schematic and go from there. Remember, some cars use fusible links or seperate fuses in another fuse box found under the hood. Also some fuses in the fuse box control more than one thing and the schematic may not even tell you this (any mechanic will tell you how inacurate schematics can be, compared to how the car is actually wired in real life.)

If theres power coming out of it then you have to trace the wiring as best you can until you find the dead spot.

[t_cel_t]

well it turned out to be that little yellow box in the trunk, the one that detects that a bulb is burned out

[wiccanferret]

Wait...you put the battery in backwards then blamed it on the parts store? Brilliant!