2008 Sierra turn signal issue HELP!

JGW · March 28, 2020

Hey all,

I just bought a 2008 Sierra 1500 XLT. The left signal flasher does not work. The right side functions fine. When the headlights are on all of the lamps function correctly. When the flashers or the signals are activated the left side flashes normal 3 times and then fast from there on. I replaced the multi switch stock on the column. When the flashers are are activated the fuse blows which tells me there is a short somewhere...I guess. Why would the lamps work if the headlights are on if their is a short? Where would I look for a short? The wires seem to be covered in a loom except at the housing itself and I did not see any bare wire or rub spots. Is the flasher split into a right and left side? If so where is the flasher control?

Any in site would be appreciated. Thanks!

Doug_Scott · March 28, 2020

You are likely confusing the parking lights with the turn signal lights. They do both use the same bulb, but, they use their own filament inside each bulb. First thing to try is to remove all the signal bulbs, at both ends of the truck, and then look inside the socket for damage or green crap. If all is good, put 4 ways on and put bulbs back in, one at a time, until the fuse blows. If the fuse blows right away, you are in for a lot of work, unless you get very lucky and find it right away. You already know it is on the left side, so that removes half of the wiring. A "short" is a lot easier to locate compared to an "open". A short means the wire is touching ground at some point. Look for spots where the wiring harness is rubbing against metal, or where it is next to the sharp end of a screw. Do not pull at the wiring until you find the area the short is in. If you twist and pull at the harness you may "fix" it, but only temporarily. You want to find the short to fix, not have it go away for an hour or so. Pay attention to spots in the harness where it attaches to the body with straps or zip ties.

JGW · April 11, 2020

Also I have no brake lights on that side.

Colossus · April 11, 2020

Check the tow light plug in the back bumper and the wires for that, trace them back make sure they are not corroded or cut or whatever.

JGW · April 11, 2020

I try that. Thanks

Doug_Scott · April 12, 2020

21 hours ago, JGW said:

Also I have no brake lights on that side.

Signals and brake lights use the same filament. Signals that flash quickly means a bulb is not working or someone has replaced the bulb with an LED bulb. If you install LED bulbs you have to install a resistor across the signal wire to ground to trick the BCM or flasher module, I don't recall which one for sure, into thinking all the bulbs are working correctly. If the bulbs have been swapped for LEDs and the proper resistors have been installed. Check those resistors and see if they are still working. The ones I have seen get real hot.

JGW · April 12, 2020

I check the reared harness. It was dirty but seemed fine. I did find a connection point above the spare with a spot in the harness that looked like a plug was spliced in. The plug looked like it had a big square cap that said delco in it. I don’t know what it is. That’s all I’ve found. I’m not an auto electrician. I may take it to a shop. Give me a Painless harness. So much simpler. Thanks!