This is a followup to this thread several months ago: Urgent help! Taillights not working in middle of roadtrip

Basically that thread is about how my tail fuse kept blowing when i was returning from this past summer's road trip (to make it back home, i replaced it with a 30a fuse). When i made it back home, i replaced the fuse back with a 10a and everything worked fine again as if nothing happened. However, last week the battery completely died (it was 3 years old installed from dealership), so i took the 4runner to the toyota dealership and told them about the tail fuse problem i had during the summer and they said they would inspect the wiring. Long story short, they replaced the battery and said they couldn't find anything wrong with the tail fuse, but said something was draining very low power from the battery for 5 hours after turning the car off but they dont know what it is.

So now today i realized the tail lights weren't working again, and pulled out the fuse and it was blown again! Just like before in the summer. When i tried to replace the fuse with another 10a, the tail fuse spot would spark and the fuse would pop before i even pushed it in all the way. This is driving me crazy. I can't find the problem and neither can the dealership. I'm going to take it back to the dealership on the weekend now that the tail fuse is sparking and wont accept any fuse, so maybe they can figure it out now. Anybody got any ideas? Anything else i can try looking at or fixing?

no replies? anyways i was thinking, could my aftermarket pioneer bt3300 radio/headunit cause this problem? I'm thinking of taking it out and inspecting all the wires. Maybe something came loose overtime and is causing a short? some of those wires were only kept together using electrical tape.

fix your crappy wiring job... also check to make sure the ground you used isn't a switched power for your parking lights. I've seen that happen before.

by sticking a 30a fuse in that 10a for your trip home, you could have melted a few wires. I guarantee they didn't use big enough wires intended to carry that much current.

edit: by the way, if you have melted wires they will be closest to the power source (your fuse box) unless the insulation has been worn off somewhere along the line.

U might need to check some relays out. It could be stuck internally.

^This^...not to shoot you while your down but that wasn't a good idea..I would refrain from doing that again, with any fuse.

I've seen shorting cause by corrosion. I'd check the connector for the taillight harness as well as the bulb sockets.

My old Corolla had a problem where the parking lights would come on every time I hit the brakes. Problem was that corrosion had bridged the gap between the two center contacts in one of the taillight sockets. I realize that's not similar to your problem but the point is, corrosion can cause shorting.

ok thanks for the responses guys! I know it was stupid to put that 30a fuse in. I didn't even think about doing that, but the folks at autozone suggested using a higher amp just to get it working again to get back home when i was still in Albuquerque during that road trip and i didnt think about it. Now that i think about it, since it seemed to work with the 10a later then failed again after a few months, it could be a wire behind the radio that came loose and is shorting something out. Would something like the radio affect the tail fuse? I'll be able to get a look at it later this weekend then i'll follow-up post if it was resolved.

Mistake number two - taking advice for autozone employees. Employment qualifications include naming three major auto manufactures and three parts located under hood and the "trick" question how many tires can be found on or in the average vehicle.

But on a serious note a corroded or a loose connection between fuse box and tail lights track down all connectors and start measuring the resistance with multimeter. You tube has a few instruction videos on this matter.

I'll be happy to explain multi meter use as well.

I'll have to see if I can find a diagram... the ground I mention is a ground if the lights are off. once you turn them on it actually ended up being a power wire for the dimmer circuit (?) (been awhile, can't remember if that was it). I imagine that may not be the problem since I'm sure the rest of your lights work. it could be corrosion at the bulb socket. kinda check it out if you can.

...And that's a reason I left the parts business even if it was a part time college job. Because I'm young, I dont know what I'm talking about so they believe the manager that's never touched a car. Or, they have worked on plenty but don't know anything. Seriously, I lost a debate on "radiator cap color indicates coolant type" (it doesn't) for a 90's Japanese car. the guy left with dexron :|

anyway...

I think mikebontoft was alluding to this in his comment, but I would check the wire you used to hook up power on your aftermarket radio.

You probably used the power wires for the old head unit, but just in case you didn't you may want to check and see what the wire actually connects to.

He also said to fix the wiring. Some people would solder the connections, but there are all kinds of connectors you can buy that tap into existing wiring and cover the connection. They are also probably more secure than electrical tape. Your choice.

You know i just re-read post i believe there is voltage on both sides of fuse terminals one side should read 12 volts and other side should have none. Im betting the other side shows some voltage being back fed from another source. I found this one time someone hacked into taillight harness for feed for trailer 4 way plug. Although Im not saying its coming from there but .....

Check the dimmer wire on the harness, both on the pioneer and the one that plugs to oem, im sure u used a metra or scoshe. Should be orange wire.

^^^What he said above. IIRC the instructions for my aftermarket unit sold by Crutchfield involved permanently taping off an orange wire.

I 've written before somewhere about my taillight adventures. Mine died when I went over a highway bump. In a fit I ripped out the "professionally" installed trailer hitch wire. It turned out to be the ground in the stereo. I had used the Metra harness. I had installed the stereo about a month before the trouble started. So when I went back into the dash nothing looked amiss. After googling for advice I cut truck side and stereo side black wires and put connectors on them, used a Dremmel to shave the finish off a spot of the truck's metal stereo frame, drilled a small hole and screwed the ground wires to that. No more burnt fuses. It has been about 5 months and every thing is working fine. Don't forget to detach the ground on your battery before doing any electrical work.

Thanks for all the great responses so far guys! Yes i used the metra kit, and there were some wires that weren't used. I also bypassed the parking brake. I'm trying to remember what i did with the ground wire. The thing is i installed the radio over a year ago, but like i said before some wires were secured using only electrical tape, so i'm wondering if over time some of those came loose and is causing a short (that could explain why the fuse blew on the roadtrip then returned to "normal" then blew again months later) This weekend i'll take it all apart and see what i can find. Just gotta wait until then...

30amp fuse in a 10amp slot? Yep, i did that when I installed my HIDs. Guess what? I melted my main engine wire harness, main harness (in the dash), 2 injectors and needed a new battery doing that. About $7K and 3 months later, I was back on the road. Lesson learned (for me). When you are unsure of electrical stuff, WALK AWAY and get help before you do damage.

It also sounds like mikebontoft is right, you may have melted some wires. Check the wires/harness for damage. I'm not trying to be a d*ck, I completely sympathize with ya. I sure hope you didn't. The "circuity" of the LEDs might be fried, if that's the case, you are lucky. I hope it's just the LED tail lights that are screwed up. (TONS cheaper to fix/replace than wire harnesses). I had the Toyota dealer check out my problem and they had to fly someone in (from Toyota) to help diagnosis the problem. They have equipment that can read the ECU and past episodes to help them see where the fault is. This is what I was told, maybe a tech can chime in here regarding that..........

Good luck, hope you fix the problem cheaply......

Many years ago I assisted an electrician who knew how to find problems in a hurry.
He would put a wire or coin in the fuse holder (replacing the fuse with a something that could handle a lot of current) and the problem area would identify itself with smoke.