this is a 63 c 10. the dash turn signal indicator is a shared bulb left and right. the instrument panel harness is original wiring. the rest of the truck is American auto wire. the turn signals are wired as shown in the 63 c10 schematic. (attached) the truck electrical works perfect except the right turn signal. both front and trail light blink but the dash indicator light does not. if i put my test light on the bulb my test light blinks bright but the bulb is very weak. take the test light off the bulb goes out. i have grounds from the batt to the engine, frame, firewall, and dash. what am i missing?
"if i put my test light on the bulb my test light blinks bright but the bulb is very weak. take the test light off the bulb goes out."
Assume "bulb" means the indicator bulb.
What does "on the bulb" mean exactly????? What kind of test light, the ice pick style? Are you pushing on the bulb glass or touching the side of the bulb case with pick and the tester clip on ground? Touching only the socket? Took bulb out and tested contact down in? These questions are important even if sound silly.
So far what you posted indicates there is a flash signal getting to the dash bulb socket for left and right. Seems bulb is good, "seems" ground is good. So will wait for test details. Seems like what you did during test has the clue. Loose bulb loose socket, Assume test described was with turn signal lever on right turn.
How are you getting to the bulb to test?????????
Best guess: Wire connections at one of the connectors or at the turn signal switch or at the dash bulb socket is partially broken, loose, corroded. So as not able to deliver a strong voltage thru bulb and into socket/chassis ground. but test bulb lights because it has it's own direct ground and maybe a different diameter filament is a low amp draw LED. The dash indicator bulb gets it's right turn signal from a Dark Blue (DBL) wire from turn signal switch (also DBL) at a double up at the firewall connector. Indicators get their signals from front turn wiring.
Last edited by bartamos; 07/09/202512:25 AM. Reason: clarification/see line thru
thanks yes the bulb means the indicator bulb. my tester is the pick style. i take the bulb holder/socket out of the dash panel, there is enough wire that it hangs below the dash. i touch the test pick on the side of the bulb where it is accessible. i also removed the bulb and tested the socket with the same results . yes the turn signal lever was in the right turn position. i have checked all the connections a couple times and all appear to be secure. the turn signal switch is new. the left turn signal works perfect.
The "side" of the bulb does not have voltage per se. It is the ground. The bayonet pins do most of the grounding. Your test light must have glowed green as you completed the ground (ice pick tip is "more positive"). Should have glowed red when touching contact down inside socket and alligtor clip on some kind of chassis ground.. If the socket and bulb is hanging, there is no ground for the socket. The test light must be supplying it. You are also not testing the "as is" ground for the socket to dash. As the bulb is hanging, add a jumper wire from the socket metal to a good known ground. No test light involved. Operate lever both ways.This will confirm a ground issue.
Report what happens
Please confirm: When bulb was mounted in dash, the left front and rear bulbs flashed bright, as well as the indicator bulb. The right F and R bulbs flashed bright but indicator did not flash. All with ignition key on. Replacing bulb with a known good bulb would be a fast check.
Last edited by bartamos; 07/09/202512:32 AM. Reason: added last paragraph
Focus hard on the wires from the double up to bulb socket. Diagram shows DBL wire from firewall connetor to one half of instrument cluster connector... thru cluster connector contacts and out to another DBL wire to the bulb socket. We know the flash signal from turn signal switch (DBL wire) is getting to that two DBL wire double up on the firewall connector, because the front right light flashes.
You can unplug the instrument cluster connector and see if the flash is reaching the DBL pin of the cluster connector half that is wired to the firewall connector. IF so, check continuity from other half DBL pin to bulb socket contact.
OR.... Cut to the chase and run a direct test wire from double up DBL to the hanging bulb socket. Make sure, as I said, that socket housing is well grounded while hanging. Key on, lever at right turn. You will be bypassing all existing wires and connectors. If it blinks then, incorporate that wire into the under dash harness. Don't bother finding and fixing whatever is wrong.
Regardless, Shine up the bulb brass case, the inside and outside of socket and where socket touches dash. Shine up the mating dash surface. Even though we see that ground is working for the left turn. Just a thorough thing to do.
Make sure all solder connections are good.
Next week.
Last edited by bartamos; 07/15/20256:08 PM. Reason: clarification
it kind of makes sense if you look at the schematic. in the turn signal circuit, it only shows a ground at the rear and front turn signal bulbs. i kind of imagined myself an electron, and where did i need to go to get to ground. anyway until the next issue. thanks rolf
What does not make sense is that you said all the lights worked but the indicator light for right did not. If right front bulb flashed and park the worked, the bulb had ground. So whatever you did or whatever happened does not matter, but it does not make sense to me. But it's moot now. I like to get knowledge on troubleshooting. Sometimes it just doesn't happen with blogging back and forth. It's a difficult part of the process. No one's fault. Fixed is fixed. Glad all is well. We welcome any next issue. thanks for the response.
