Fast Blinkers when Headlights are on?

I just got a 2000 Silverado 1500 3-door (5.3 w/ automatic).

When the headlights are off, the turn signals work just fine.

But whenever the headlights are on, the turn signals blink really fast, with the dashboard indicator of the opposite (unused) blinker faintly lighting up along with the correct one lighting up as it should. For example, with the left blinker on, it blinks really fast and the right indicator is faintly lighting up as well - and same for the right blinker.

Any idea what's going on?

I just got a 2000 Silverado 1500 3-door (5.3 w/ automatic).

When the headlights are off, the turn signals work just fine.

But whenever the headlights are on, the turn signals blink really fast, with the dashboard indicator of the opposite (unused) blinker faintly lighting up along with the correct one lighting up as it should. For example, with the left blinker on, it blinks really fast and the right indicator is faintly lighting up as well - and same for the right blinker.

Any idea what's going on?

I would check all the lamps to make sure the proper lamps installed and installed correctly

OK, all bulbs are correct and properly installed. Problem still exists.

Even more - In addition to the inside blinker indicator going too fast and the opposite blinker indicator lighting up faintly - on the outside of the vehicle, not only are the blinkers going fast but the opposite side blinkers are alternating on/off as well (but not quite as brightly), kinda like an emergency vehicle with left/right/left/right strobes. Additionally, the DRL bulbs are coming on very faintly in sync with whichever turn signal is selected. :runaround:
* Makes me not want to use the turn signals at night - they'd just be confusing to other drivers.

Here's when it acts up, as far as I can tell so far:

Daytime with the headlights off and DRL's on, the blinkers work fine.
Nighttime with the headlights on and DRLs off, they act up and try to light up the DRLs
Nighttime with the headlights off and DRLs off, they work fine - but try to light up the DRL bulbs.

I've got a Service Manual, and have looked at the various wiring diagrams, and as far as I can tell the only thing the Headlights, DRL, and Turn Signals have in common is the ground, which is also shared by 8-9 other things that are working fine.

Ideas?

you got me on this one !

possible the BCM is defective or shorted wires there...

Might want to try a new headlight switch, or one from a salvage yard, see what happens.

Like the j cAT says it's kind of a stumper.

on the rear of the bed under , in spare tire storage area is a junction circuit board / connector interface for the rear lights. check this out for damage corrosion . some have report this causing strange lighting failures.

Sounds like a bad ground on the lights.
Does it happen the same for both directions?
Bob B

I'll check the rear junction block this weekend, as well as pulling the grill and headlights to look for anything amiss.

Yes, it's the same for either side blinker.

Reminds me of a '71 MGB we used to own.... :iceslolan

Ok, here's an update...sigh...

Found that the ground wires at the front left side (under the radiator support) were broken. Repaired the wires, and got good grounds for both sides. The rear ground looks fine.

It kinda fixed it...

Now, when the park lights / headlights are on and the turn signals activated, the Front Park Lamps and Turn Signals on the proper side alternate really fast, as well as the Rear Taillights and Turn Signals.
The dash indicators are working properly, no more L/R alternating there.

Probing around with an ohm-meter, I'm finding that on both front side-markers, both the brown and blue wires are connected to the grounds. From looking at the wiring diagrams (I have a service manual), neither one should connect straight to ground, but back to the FR Park or Turn fuses.

Ok, here's an update...sigh...

Found that the ground wires at the front left side (under the radiator support) were broken. Repaired the wires, and got good grounds for both sides. The rear ground looks fine.

It kinda fixed it...

Now, when the park lights / headlights are on and the turn signals activated, the Front Park Lamps and Turn Signals on the proper side alternate really fast, as well as the Rear Taillights and Turn Signals.
The dash indicators are working properly, no more L/R alternating there.

Probing around with an ohm-meter, I'm finding that on both front side-markers, both the brown and blue wires are connected to the grounds. From looking at the wiring diagrams (I have a service manual), neither one should connect straight to ground, but back to the FR Park or Turn fuses.

so with the headlights on, the directionals for both sides , when activated flash too fast ?

also why did these wires get damaged . body shop ? rodent ?

Aha, SUCCESS!!!

I went back to that front lamp ground, and got all obsessive-compulsive about rebuilding it - re-cleaned wires, replacing the ring connector, and soldering the joints. Also moved the ground location (bolt) back to the factory location at lower radiator support - it was bolted into the upper radiator support. Not sure if that makes much difference since there's also a direct battery ground cable under the same bolt.

Put it all back together, and now it works properly - either I didn't have a good enough ground the first time around, or there's something magical about the lower radiator support.

To answer your questions j Cat;

Yes they were flashing too fast, also at the rear the tail-lights were joining into the flashing (not supposed to). I found out that the front Turn Signal and Side Markers are supposed to alternate.

And the original problem(s) were caused by a poorly-done body shop repair, a good example of what I call "Crapsmanship".

Aha, SUCCESS!!!

I went back to that front lamp ground, and got all obsessive-compulsive about rebuilding it - re-cleaned wires, replacing the ring connector, and soldering the joints. Also moved the ground location (bolt) back to the factory location at lower radiator support - it was bolted into the upper radiator support. Not sure if that makes much difference since there's also a direct battery ground cable under the same bolt.

Put it all back together, and now it works properly - either I didn't have a good enough ground the first time around, or there's something magical about the lower radiator support.

To answer your questions j Cat;

Yes they were flashing too fast, also at the rear the tail-lights were joining into the flashing (not supposed to). I found out that the front Turn Signal and Side Markers are supposed to alternate.

And the original problem(s) were caused by a poorly-done body shop repair, a good example of what I call "Crapsmanship".

thats why I asked about body work..electricity and body shop work is a bad situation ...

good luck ...another wierd electrical problem solved by correcting bad / defective grounds...typical !