Tail Light Positive Shorted

Hello everyone, First-time poster here. My truck is an 04, Prerunner SR5 with the 5VZ and diff locker.


In a quick sentence, I shorted the positive lead on the light under the transmission gear selector to the ground while it was on.


Now for the longer version.


I have a couple of backlit rocker switches, which I previously wired to turn on with the running lights, and everything that comes on with those. (gauge cluster lights, ac panel lights front running lights, and rear running lights, (not sure if running light is the correct term or not)). They worked perfectly until a couple of weeks ago when I went to add another one and accidentally shorted the 12v, of which I was taking power from the light under the gear selector, to ground. Guess I forgot to disconnect the battery.. whoops.


Also thought it was worth noting that I have replaced every single bulb in the truck with the LED equivalents, and all the lights still work if I feed 12v directly from the battery into the line that I shorted (I currently am utilizing this as a temp fix, just routed 12v from battery to the gear selector light through a switch to turn on the tail lights when I need to drive at night).


I am not a genius with electrics, especially when it comes to troubleshooting, but the following is what I have checked so far:


- Continuity between tail light positive and ground

- none present

- Every fuse in the block under the hood, and behind the driver kick panel

- all good and not blown


On doing problem research I saw that some people had similar issues and said that it was due to a chip on the body ecu blowing. I couldnt find any other leads, so I went on eBay and bought one. Replaced it, and unfortunately, it did not fix the problem. Fairly certain that this kills it from the list of possibilities, hopefully they didn't send me a non-op unit.


Now I am at a loss for what to do. I bought a wiring diagram book from eBay and will try to flip through it and find any other possibilities when it arrives, but Until then if anyone has any ideas on what I might want to look for/test/replace, I am all ears and am down to try anything.

 

Welcome to the forum!

Your saying you have no tail lights ?

Nothing works at all to you bypass the switch and tail light relay with direct system voltage ?

Your saying your short caused no circuit protection to open ? You stopped the short by separating the wires ?

You have an open circuit between the power source and where your attaching your jumper wire .

Could be a failed tail light relay a failed switch or a burnt wire or a fuse you missed.

i would add circuit protection to your jumper wire as that circuit has none.

 

To the no tail lights, Yes but only kind of. If I bypass the switch and feed voltage directly all the lights turn on still, which leads me to believe it is not a burnt wire. Also is not the switch, as when I turn the tail lights on, I can hear the tail light relay actuate. The wiring diagram book came as well and I was flipping through it this morning. If the DRL is what runs the tail lights (pic below), then it appears there are a couple of relays up under the dash, may take a look at them soon as well. Good idea on the protection, I'll drop a fuse inline later. Still iso the problem

 

Just because you hear a relay pull in doesn't mean the contacts are not fubar
The DRL circuit should not effect the tail light circuit at all

 

It's possible you did something to the rheostat for dimming the lights. The illumination circuit uses a floating ground to dim the lights. You said you touched the power for the gear selector light to ground. Was this a Green-Red Stripe wire? This wire gets power from the 10A tail fuse and is also directly connected to the Rheostat. Recheck the 10A tail fuse (just swap in a known good one to eliminate that as a possible problem). Inspect the rheostat and potentially just swap in a known good one. If you have a multi-meter then check the voltage at the rheostat using the diagram attached.

 

It was a green red wire that I took power from, so I think your wiring diagram is good. Also took out the rheostat and tested the potentiometer. Values were not right so I think that may be the problem. Ordered one from my local dealership and it should get here tomorrow. Thanks for the help, keeping my fingers crossed!

 

Since the rheostat does not effect the tail lights this will be intriguing.

Best of luck

 

Well it could if it was shorting to ground, providing an alternate route to ground instead of through the tail lights. But if connecting temporary power to that wire makes the tails work, then it might not be the rheostat.

G-R is power for illumination.
W-B is ground
W-G is the floating ground. When you put a multi-meter between the G-R and W-G you will get any value between 12v+ and 0 depending on the position of the rheostat.

Looking at the diagram again, you must have a break in your power wire sometime before where you temporarily connected power. This could be on the Green wire between the Tail fuse and front parking lights, or the junction block where the green wire connects to the G-R. Or it could be on the B-W wire between the tail relay and the tail fuse. Do your front parking lights work with your temporary power?

You said you could hear the tail relay click when turning on the running light switch, can you confirm this is working? Find the B-W between the tail fuse and tail relay and see if you get 12v before the fuse. Then check that you have 12v after the fuse. Then keep going. You need to trace your power source until it stops and you'll find the problem.

All of this points towards a bad tail fuse or relay FYI. You need to confirm these are absolutely working. Don't just look at the fuse, you need to test continuity through it.

Other things to test:

Ground the Violet-Red wire out of the body ECU
Do the running lights turn on? No = bad combination stalk switch

Ground the Red wire out of the Tail Relay
Do the running lights turn on? No = bad tail relay, Yes = Bad Body ECU

 

A short to ground means open circuit either a fuse or burnt wires.

 

Got the new rheostat in today, plugged it in, and believe it or not, everything turned on and worked as it should! Still a little confused about how this happened, given that if it was a short to ground in the rheostat, it would cause a fuse to blow, and like Bivouac said it doesn't appear to be in line with the taillights, but hey, it works now, I'm not gonna question it.

I did find some aftermarket wiring running around through the dash when I had everything apart, must have been from previous owners, so that could have been part of the problem as well, but again it works, I'm not gonna question it.

Couldn't thank you two enough for all the effort and time you've put into my problem!

 

Welcome to TW

 

Awesome! I'm glad it was as simple as swapping the part. I really didn't make sense to me either, it should have blown the Tail fuse.