Electrical problem, blower speed selector causes abs and brake lights come on.

mitchmxz · March 16, 2020

I have an 04 gmc Sierra Wt with a weird issue.

it started when my battery went bad. i use the intermittent pin in the body-12 way-brown in the cab fuse block as an ignition driven accessory.

the first thing i noticed was the accessory would only work every now and then.

next the blower stopped working, the abs and brake likes came on, all at the same time.

after messing with it all day here is the current issue.

the abs and brake like come on when the blower speed control it set to any speed other then 0. when set back to 0 the abs and brake lights will turn off.

the intermittent pin on the body-12 way-brown has low voltage and cant power my accessory.

the constant power pin next to the intermittent pin has full 12 volts.

I have checked every fuse and cleaned the ground on the forward driver side and the ground in front of the driver side suspension.

I have also added 3 ground wires

cab to battery

frame to battery

block to battery

I am at a lose for what to do.

Could it be a bad relay?

riverbanks · March 16, 2020

What's the accessory?

Doug_Scott · March 16, 2020

Chances are whatever is causing your issue likely helped take the battery out.

Pull the fuse panel under the hood and flip it over. Look for corrosion on all the connections. If it is bad, you will see white powder around the connections.

What gauge wire did you use for the grounds? Did you pull the battery ground cable from the engine and twist the lug connector around looking for white powder to come out? If the insulation is starting to bulge, cut the bulge and you will see corrosion.

Any ground wires that you add should be at least 10 gauge. The battery ground cable should be big enough to handle the big amperage circuits. Remember if you add another ground wire to a specific location, it must be big enough to handle the amperage back to ground.

mitchmxz · March 16, 2020

1 hour ago, Doug_Scott said:

Chances are whatever is causing your issue likely helped take the battery out.

Pull the fuse panel under the hood and flip it over. Look for corrosion on all the connections. If it is bad, you will see white powder around the connections.

What gauge wire did you use for the grounds? Did you pull the battery ground cable from the engine and twist the lug connector around looking for white powder to come out? If the insulation is starting to bulge, cut the bulge and you will see corrosion.

Any ground wires that you add should be at least 10 gauge. The battery ground cable should be big enough to handle the big amperage circuits. Remember if you add another ground wire to a specific location, it must be big enough to handle the amperage back to ground.

no corrosion in, on, or under the fuse box.

I don't know the exact gauge of wire but it is plenty big enough.

Edited March 16, 2020 by mitchmxz