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Discussion Starter #1
This problem has been reported before, but I had some questions, and I'm stuck.

2003 Trailblazer, I6, Short wheelbase, 100,000 miles. Salt Driven truck. :(
Truck runs great in the day. Starts. AC works. Signals work etc etc.
Newer Battery and New Alternator (1.5 yrs ago).

Suddenly a few days ago..
-When the headlights come on at night (auto headlights), I see a faint left turn signal light on the dash constantly illuminated. About 20% of when you turn on the indicator.
-When I turn on the left signal, the headlight flashes with the turn signal. Yes. Headlight!
-When I use the right turn signal, everything is fine.

- When I turn on the highbeams, the RPM's start dropping and the truck stalls.
  • When I turn off the highbeams, it starts right away and idles perfect (625rpm)
  • There is always crank, but the motor won't fire in this case (Highbeam on)

- If I unplug the entire headlight assembly from the Truck, the TB will crank, but not start.
If I plug it back in, it starts right up. The very first time, after I unplug the lights, the truck will briefly start, but stalls. Residual fuel?

- Unplugging bulbs can still cause the truck to stall (Highbeam on)

Fixes So Far, but no luck
A) Removed and Cleaned out the throttle body to ensure proper idle. Runs great!

B) Cleaned both Chassis grounds under the B Pillar and ABS module.

C) Cleaned both body grounds on Inner fenders (Left and Right)

D) Cleaned body ground on the firewall near the brake master.

HELP.... :)
A) Could the issue be inside the fuse box? One of the traces? Any idea which trace could it be.. Fuel pump, PCM ????

B) Headlight Assembly itself?

C) Another ground I'm missing. Shall I ground out the headlight left assembly and test it?

D) Other???

2 Posts
Discussion Starter #2

After a bunch of testing (and without taking apart the Fuse Panel), I grounded the Highbeam Ground line to the Body with a new wire. This is the main connector that runs into the headlight unit at the bottom (Black 4 wire plug, with 2 ground wires).

Truck fired up right away with the headlight disconnected (as it should).

I plugged the headlights all back in, and everything works as it should.

Headlight Circuit-fix2.jpg
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