03 Corolla Dash/tail Light Fuse Keeps Blowing

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I've got a real bad problem right now with my dash/tail light fuse. Last year this fuse blew once, we replaced it and it worked no problem. This year it blew again, replaced it and it worked. But shortly after that, maybe a couple of weeks it blew again. And after that, every new fuse we put in would instantly blow.

Took it to the mechanic-they looked at the wiring, installed a new instrument cluster (he claimed the old one had a short in it, but that clearly was not the problem) and sent us on our way. Well my fuse blew as soon as I got my car home.

Took it to the shop AGAIN, this time it was there for a week, and they said they can't really find the cause, but that perhaps its the wiring from my sunroof that is causing the problem. My sunroof was put in by a Toyota dealership when the car was bought brand new.

After the second time at the mechanic, a new problem came up from whatever they did. Now, no matter what setting you have my dimmer switch on, the overhead light will. not. turn. off. Ever. So they took out the bulb of my overhead light so it wouldn't be on while I was driving. Oh and then my fuse blew again once I got my car home. The mechanic said they tried as hard as they could to get the new fuse to blow and they couldn't. But it pretty much instantly blows as soon as I drive my car.

The stereo system is original, nothing has been changed or added. The only thing that I have in my car that is different is, I just got a new phone so I have a new charger in my car that I plug in to my cigarette lighter. Now, I don't know if that could be in any way related to what is going on but that is the only new thing I have in my car. It's not like the fuse blows as soon as I plug my phone in or something.

Does anyone have ANY ideas at all? I need my car every single day and I can't keep it in the shop this much!

Guessing from your description - sounds like your integration relay is toast. This is a major electrical junction that most of the interior lighting and gauge runs to, as well as some of the body logic. Just do a search for it online and you'll this is a pretty decent sized component. Many of your interior electrical systems run to this, and would be the very first thing I'd check out.

These integration relays generally don't have any problems (no moving parts, etc.), but if they do - you'll see funny electrical behavior like you've just seen. My fear is that the mechanic has complicated the issue by introducing a new problem / swapping parts. Electrical diagnostic work is hard and in cases like this, can be a nightmare to properly diagnose.

From the initial issue - definitely the wiring that is connected to that branch (fuse) is shorting somewhere. Mechanic should have traced that wire from the tail assembly all the way back the integration relay. Visually inspected to make sure the wiring was OK, no discoloration in the wires.

You might be lucky and look at the wiring running to the integration relay and see if any wires are charred. Since it blows when you are driving the car, it should narrow down the circuits to looks for.

Unfortunately, I can't help you much past this - really need to see the car in person to point you in the right direction. My suggestion is taking it to a shop that specializes in electrical diagnostic work, not just a general repair shop. Electrical diagnostics can be extremely time consuming - most shops don't want to deal with those as they eat up too much time.

Aside from the integration relay - could be almost anything at this point. Water that got into the wiring, short from a bad circuit in the car's body logic, bad switches, wiring that saw too much current and blistered the jacket insulation, pins that pulled out of connectors, faulty charging system, faulty sensor, cross-wiring issue from a completely unrelated system (ie, power door lock could have a short in it and manifest as a blown fuse for the tail/light assembly), faulty radio, damaged power points (outlets), corroded bulb sockets, bad chassis grounds, etc.