I installed a light bar in my 4runner. I wired it up connected via a switch and a relay only to the positive terminal of the battery and the spot where the negative terminal of the battery is grounded to the passenger side fender well. The switch I used (Toyota 00550-35976) has a little light on it, but I figured it wouldn't draw enough to be a problem being connected to an always-on +12V source instead of one that was switched with the ACC or RUN key positions, so I left finding a way to connect it to one of those instead as a future project.

After the installation, the light worked fine and the truck worked fine. (I know this because I drove it to park it somewhere else.)

A day or two later, I tried to use it and it wouldn't start. The battery wasn't completely dead, but it wouldn't turn over.

A while later, I tried to jump-start it and it wouldn't turn over even with the other car powering it.

Then I used my trickle charger to charge the battery, which is now reading 12.8 volts. Even so, the truck not only doesn't start, it has no electrical power at all -- not even for the dome light or power door locks. (I don't remember if it was that dead while trying to jump start it or not.)

I've tried disconnecting the light I installed; no change.

I assume it must have blown a fuse or something (hopefully I didn't manage to fry the ECU somehow), but I'm not sure which fuse it would be or where to start troubleshooting it. Help?

 

Which fuses did you check? (don't say "all of them." You don't even know where "all" of them are.) How did you check them? (if your answer doesn't contain the word "multimeter," go back, start over.)

Frying the ECM is very unlikely to cause "no electrical power." More likely, you've blown one or more fuses, or even more likely (given the description of your installation) the fusible link. Start from the battery, and check for battery voltage at points (electrically) farther and farther from the battery. That method can find a blown fuse, or even a broken wire.

 

This might be a stupid question, but how do I remove the larger fuses to check them? (Not the spade fuses; I know I can use the little plastic tweezers on the underside of the fuse box cover for those.)

Last time I tried to just yank on something to remove it, I ended up breaking the cover off a relay instead of pulling the relay out of the socket, so I hesitate to use brute force.

 

Actually, no it isn't.

They're bolted in; you have to get at them from the bottom of the fuse holder. Here's pix: https://www.yotatech.com/forums/f116...cement-228307/