Turn signal issue

[ed455]

1999 C3500 LS Crew cab 7.4L

ORIGINAL CONDITION:

1. Turn signals work perfectly with headlights OFF.

2. Left turn signal hyper-blink with headlights ON.

3. All bulbs (incandescent) - good

4. Oem thermal flasher.

MODIFICATION 1

1. New Spyder glass headlights and Sylvania Silverstar Ultra bulbs (9005/9006)

2. Standard 4-hi modifications.

RESULT - Hi-4 mod works perfectly. No turn signal change, none expected.

MODIFICATION 2 -

1. New clear front parking/turn signal housing with replacement LED amber bulbs.

RESULT -
Both sides hyper-blink with headlights OFF.

Left signal no blink at all with headlights ON.

Right side hyper-blink with headlights ON.

NOTE- I expected hyper-blink with the LED bulbs.

MODIFICATION 3

Replace thermal oem flasher with electronic flasher compatible with LED bulbs.

RESULT

Both side blink perfectly with headlights OFF.

Right side blinks perfectly with headlights ON.

Left side NO BLINK with headlights ON.


TESTS

Disconnect trailer light plug. NO CHANGE.

Disconnect rear tail light harness. NO CHANGE. (Flasher is electronic no blinks on dash with or without bulb resistance)

I'm suspicious of my turn signal switch, but a Delco oem switch is $250 and non-returnable, the aftermarket replacements are $60 but I'm suspicious of quality.

Anyone been through this problem and SOLVED it? I've searched the interwebs and found it's a common problem, but find no definitive solutions. I've rewired entire vehicles with up to 18 circuits and installed aftermarket EFI so I know my way around 12v wiring. But this one has me stumped so far. The grounds I have located all seem good, also, but that doesn't mean I've found them all.

 

[ed455]

So, gonna reply to my own thread with the solution I finally found.

The LR connection at the tail light board was wonky. I cleaned and tweaked the pins and that fixed it. If it goes back to the same condition, I'm gonna replace the board in the light.