07 tacoma tail light fuse blows instantly when switch is turned on

My 10A taillight fuse blows instantly when light is switched on. Brake lights, turn signals, head lights, hazard lights all work. I have replaced my bcm and taillight bulbs. I have disconnected both license and both rear light connectors to try and eliminate a short etc in one of the rear hanesses. I visually inspected the wiring from rear forward as far as possible. I would like to follow wires to and from bcm. Does anyone know how to find the input and output connection pins and wires...i think they are green going out, but thats all i know? Does anyone know where the tail relay is located or whether this could be an issue? I do have an after market clifford alarm hanging off my bcm, but i'm not sure this is wired to the taillights. Thanks.

 

Blowing 10A rated fuse is a lot of current, especially for a simple tail light circuit. Did this problem appear out of nowhere or have you changed anything with your truck that caused this problem to show up? I would suggest removing both tail lights at the connection point and see if the fuse still blows with nothing connected to it. If it still blows, you know it's nothing with your tail lights. I would take a multimeter and test the plug for any shorts to ground. If you're blowing 10 amps I'm going to assume you have a short somewhere.

 

First thing to check is anything aftermarket installed, followed by anything you've recently worked on. It's rare for anything factory to fail in that manner, almost always add on stuff. Aftermarket trailer harness?

 

It has a factory trailer harness, I believe. It also has an after market alarm. Both of these have been there since i bought the truck 3 yrs ago.

I think the culprit could be the alarm, and possibly on the switch side of BCM, here's why i suspect that. I disconnected both 1c and 1d plugs from bcm, which i ?believe? to lead to the parking lights and tail/license lights respectively. Fuse still blows immediately when switched to parking/tail mode. I also disconnected the plugs at the taillights and license too and fuse still blows.

I think my next step is trying to figure out the wiring coming down the column through the alarm to the bcm...anyone have any experience with this?

 

I finally figured this out today. My son replaced the factory stereo awhile back and we pulled it again tonight, as i traced the green tail light switch wire from the column up through the dash. I first noticed an orange wire hanging freely, without tape or wire nut from the stereo harness. I then noticed a green wire running from the dash that was melted and fried to other wires in the bundle to the stereo harness. I noticed these two were opposite one another on the aftermarket connectors...I then taped the green wire on all fried areas and added a wire nutt to the free open wire ( I had no idea where to connect it). I replaced the tail light fuse again. This time, no popped fuse...so I guess I fixed it.

 

Glad you found the cause, but you might want to go one step further. Wire nuts are acceptable for home use, but not automotive use. I'd recommend replacing any wires that were burned or had the insulation compromised with new. I'd also recommend splicing those sections in with soldered / heat shrink insulated connections or at a minimum, heat shrink solderless connectors.