Turn signal issue.

[desert-rat]

For a 1972 C10
Regarding the left turn signal...only the tail light signal works. The fender and front bumper does not work. New bulbs also. Where about would I check or fix? Thanks.

[truckster]

If the rear works, you know the turn signal and flasher are working. Start at the socket by checking ground. Then check backwards from the socket to the wiring harness looking for 12v.

EDIT: With a 72, the front turn signal should ground through the side marker light, IIRC.

[Rust_never_sleeps]

FIRST, make sure the fender lamp is actually supposed to blink(some years it's a marker lamp)
Since you already know the switch works:
I always start with verifying a clean ground(to the body) at the socket
I'd then start at the bulkhead connector with a trouble light and "climb the ladder" out to the sockets.
I religiously spray contact cleaner into every connector to clean it, then hit it with CRC 2-26 to prevent moisture from creeping back in(I'm sure other light oils work the same), and I don't even live in a humid climate :shrug:

[Rust_never_sleeps]

Originally Posted by truckster

if the rear works, you know the turn signal and flasher are working. Start at the socket by checking ground. Then check backwards from the socket to the wiring harness looking for 12v.

jinx! ;-)

[truckster]

Originally Posted by Rust_never_sleeps

jinx! ;-)

Yep; the majority of electrical issues I find on vehicles are bad grounds.

[RustyPile]

If the rear works, you know the turn signal and flasher are working

This is incorrect. The rear turn signals and brake lights share the same wiring, and their function is "decided" by the turn signal switch.. The front turn signals work independently from the rear. A failure of either "end" and the other end will continue to operate. Also, the turn signal indicators in the dash share their circuit/power with the front. If your left turn dash indicator works properly, your turn signal switch is not the source of the problem.. If it doesn't work, suspect the signal switch.

For the following, refer to the wiring diagram for your truck. You might have an open in the light blue wire as it works its way forward to the light socket. Here's how to test the circuit. Do not disconnect the plug but locate the light blue wire at the turn signal harness plug. Turn on the key and the left turn signal.. With a test light or DVM, test for voltage on the light blue wire.. If no voltage, the T/S switch is bad.. If there is voltage, Remove the fuse box, and test for voltage on the light blue wire at the firewall connector as indicated on the wiring diagram. If you have voltage on both halves of the firewall connector, check for voltage at the bulb socket.. If you have voltage, check the ground path through the side marker light if it's part of the turn signals.. As always, check, check, check the ground paths.

[PanhandleShantyman]

When I got my '69, most of the lights in it didn't work, and in almost every case the fix for the issue was corroded grounds. Mostly the wiring to the bulb carries the positive current, but ground just happens through the housing which gets corroded with time. 80% of my electrical stuff started working when I pulled the housings off and sanded all metal points clean.