Weird problem. Ideas?

So I bought my 1998 SR5 3.4 4x4 Extracab and the guy tells me if the heater is on and you put the right turn signal on it will kill the engine. Sure enough, if the fan is off no issues and the signals work fine. A mechanic did a lot of digging around and determined it was a short in the heater control assembly. He checked every bit of wiring and didn't find any issues. So we installed a different one and no change. He now says it has to be the body control module. I don't have a clue if I should go further down this road or not.

 

Don't turn on the heater??? Issue sounds deep...

 

??? Make sure you have a good ground. From the battery to block, block to the body or frame. I find it odd that you are not blowing fuses. I know a bad ground from the block to the firewall will stop the engine.

 

No blown fuses. No wiring issues whatsoever until the heater is on and using the right turn signal. Turning left there is no problem.

 

is your key switch on the column or the dash next to the column? Maybe something is overheating and cutting of the power to the engine. Wires to the switch or in the column?

 

Key switch is on the dash next to the column. The wiring has been gone over pretty carefully but no glaring visible problem.

 

The engine dies instantly when the right signal is used.

 

Take the right side turn bulbs out and see what happens. You won't be pulling much current, other than the dash and see if it still dies. Are you loosing spark to the plugs, or is the fuel pump cutting out.

 

Id try to run a new hot wire to heater control bypass body control module if it works fuse it and run it till you find a bcm used or in junkyard

 

Wow Mr. Italiano,

You, certainly, have a crazy problem. In theory, you have Toyota intelligence making a wrong decision when the heater is on, and the right turn indicator is selected. Unfortunately, it is most likely a computer problem since these Tacomas are too new to use relay switches. If they did, you could just replace the guilty switch. I am sorry I am not a better electrical engineer to further help you out. There are some good ones that are members on this site, though.

Good Luck,
Paul