Fast blinker, grounding issue?

Mike Veator · October 25, 2017

I drive '07 Sierra, new body style and I'm having an issue with the turn signals. They both blink fas like a bulb is out. I've checked all the bulbs myself, including the sidermaeker lamps in the headlight assembly. Those were blown, so I replaced them. Still no dice. Furthermore, they don't light up even with new bulbs. I pulled them again and checked them and I didn't blow the new bulbs. I put a multimeter in the socket and no juice. My thought is maybe it's a grounding issue? I don't really know though. Or even where to look if this is the case. This is a little beyond my scope of knowledge.

Jet-X · October 25, 2017

Turn signal flasher/relay? See your owners manual for the location. It's usually under the dash near the e-brake.

SpartanAutoworx · October 25, 2017

Could be a bad BCM if its not wiring.

sefiroxx · October 25, 2017

Could be a bad BCM if its not wiring.

Probe both terminals to a direct ground (not to each other). This will determine if power is getting to the socket. The ground maybe switched and you'll need to backtrack the ground cable if power is present. The computer reads voltage on the ground to determine that there is working bulb.

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Mike Veator · November 9, 2017

I've verified that there is power to the socket. Still no dice with the blinker turning it on. Interestingly enough they come on with the daytime running lights. I figured this out after trying the lights every which way. I possibly could. Would LED tail lamps cause this? I don't know if they are factory or something a previous owner installed.

SafetyGuy · November 9, 2017

More than likely your LED tail lights are the culprit. Not enough resistance on the circuit.

GhostWriter · November 11, 2017

On ‎10‎/‎25‎/‎2017 at 4:43 PM, SpartanAutoworx said:

Could be a bad BCM if its not wiring.

There's no relay on your truck, in the traditional sense. The process is BCM controlled; but, the circuitry buried in the under-hood fuse panel has more to do with turn signal function than you might think.

If everything else checks out, you may want to look for signs of rodents nesting within the panel, or wires chewed underneath the panel. Also, shorts have been known to occur after rodents urinate inside there. In this case, the panel would have to be replaced.

Edited November 11, 2017 by GhostWriter

Arth · November 11, 2017

On my 2006 Avalanche I've been noticing the plastic wire loom has been breaking off exposing the trucks wiring. Found most of this in the engine bay but a few other places underneath the truck as well and in the cab. This actually caused me to lose my gas pedal position sensor.

Might want to start taking a look at the wiring in your truck too. My truck is garage kept in the south but age gets everything.

no HD · November 11, 2017

The LED tail light bulbs are probably causing the fast blinker issue. They don't pull the amperage that the incandescent bulbs do. People have wired in resistors to make them blink properly. Also the side marker lights sometimes use as a ground the turn signal circuit. One wire is hot with the parking/tail light circuit and the other wire is getting it's ground from the filaments in the turn signal bulbs. Then when the turn signals are flashing that's why you get the alternate flash from the marker lights when the headlights are on, because both wires are hot when the signal is flashing. When the headlights are off the side markers blink with the signals because they are using the filaments in the parking/tail light for ground. It's similar to a trailer without a proper ground and everything blinks opposite. Sorry about the long post. Not very gifted when it comes to writing. Maybe try putting incandesants back and see if that resolves both issues, if it does and you still want the LED's wire in a resistor.