Turn signals flash all four light when left turn signal activated on a 2002 silverado chevy. I have swapped the combo flasher with a known good one could it be the switch?

These vehicles were known for faulty hazard switches. They would cause an intermittent turn signal flash when you hadn't activated turn signals or they would prevent the turn signals from working at all. Operate the hazard switch and see if the turn signals work again. If so, replace the hazard switch

Have you checked the flasher? Not positive on your model, but I know some vehicles have a separate flasher for the hazards and the turn signals.

You might possibly have a bad flasher module.

You probably need a turn signal / hazard flasher module located in the under hood fuse box. These go out all the time .
Turn Signal/Hazard Lamps
The IGN E 10-amp fuse in the underhood fuse block supplies battery positive voltage to the turn signal/hazard switch assembly. The FLASH 25-amp fuse in the instrument panel (I/P) fuse block supplies battery positive voltage to the turn signal/flasher module and ground is supplied at G200. When the turn signal switch is placed in either the LEFT or RIGHT position, a voltage signal is completed from the turn signal switch to the turn sign/flasher module. When the hazard flasher switch is activated, a ground signal is completed from the turn signal/hazard switch to the turn sign/flasher module. The turn sign/flasher module then sends an on-off voltage signal through the LT TRLR, RT TRLR, LT TURN or RT TURN 10-amp fuses in the I/P fuse block to the appropriate turn signal or to all 4 fuses for hazard operation. The instrument panel cluster (IPC) indicators receive voltage from the LT TURN and RT TURN fuses as well as the driver door module (DDM)/passenger door module (PDM) for the mirror turn signals. The DDM/PDM has no function or control of the mirror turn signals other that a pass through connection for the circuits. The audio chime is also activated when the turn signals are ON. When the hazard switch is pressed, all turn signal lamps will flash including both IPC turn indicators. The front turn signals are grounded at G100. The rear turn signals are grounded at G401. The Mirror turn signals are grounded by the DDM/PDM.

Service Information
2002 Buick Park Avenue ' Park Avenue (VIN C) Service Manual ' Body and Accessories ' Lighting Systems ' Description and Operation ' Document ID: 643323


Turn Signal/Cornering Lamps
The HZDT/SIG fuse in the fuse block - underhood - left supplies battery positive voltage to the turn signal/hazard flasher module and have ground at G202. The turn signal lamps may only be activated with the ignition switch in the ON or ACCY position. The T/SIG fuse in the fuse block - underhood - left supplies battery positive voltage to the turn signal switch. When the turn signal switch is placed in either the left or right position, current flow is from the turn signal switch assembly to the turn signal/hazard flasher module. The turn signal/hazard flasher module then sends an on-off voltage signal to either the left or right turn signals and their instrument cluster (IPC) indicator. When the hazard switch is pressed, all the turn signal lamps will flash including both IPC turn signal indicators. The left turn signals have ground at G106, G400 and at G402. The right turn signals have ground at G105 and G400. The turn signal switch supplies battery positive voltage to the cornering lamps, the left cornering lamp has ground at G105 and the right cornering lamp has ground at G106.











2002 Buick Park Avenue ' Park Avenue (VIN C) Service Manual ' Body and Accessories ' Lighting Systems ' Description and Operation ' Document ID: 643323

ck your turn signal switch wiring connector because it is more than likely has been hot and melted some connections.

Replace the flasher relay. It is usually under the dash. Follow the clicking sound when the flasher is on. It just unplugs.

to the left of the steering collum connected to the under collum kick panel as you take the panel down it'll be connected to the cover, It's not a genaric flasher, it's square and looks like a relayCost about 6 bucks at the parts store. If the turn signals aren't flashing and they do come on, and may be they flash on one side and not the other then it's not the flashers fault. All the light bulbs have to work or it won't flash and thats how you know that thiers a bulb out. Turn on the four ways flashers (Hazard lights ) and walk arounf the car and see if thier all working and flashing brightly. They'll flash anyway on four way the switches are known to hang in hazard and not work right on turn signal so try switching ti a few times and maybe it'll straighten out. If it flashes at all the flasher is good and if they don't even light not on hazard or turn the flasher and or the fuse is bad.

View wiring diagrams an using a DVOM - digital volt ohm meter is the normal way to find this type problem's. If unsure on how to proceed watch these video's Electric Testing Techniques You Need to Know
Basic Electricity for Service Techs Ohm law Current Flow Opens Shorts
Free wiring diagrams here http://www.bbbind.com/free_tsb.html
Enter vehicle info. year , make , model an engine size . Then under system click on lighting ,then under subsystem click turn signals .Click the search button then the blue link .Looking at the wiring diagram i see the BCM - body control module make's the turn lamps in the rear work .

The combo turn signal/lights/cruise stalk (and anything else on there) is probably bad or rapidly headed that way. Not a cheap fix.