Turn signal issue.
 

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.

Re: Turn signal issue.
 

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.

Re: Turn signal issue.
 

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:

Re: Turn signal issue.
 

jinx! ;-)

Re: Turn signal issue.
 

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

Re: Turn signal issue.
 

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.

Re: Turn signal issue.
 

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.

Re: Turn signal issue.
 

Here's a little twist to the LF turn signal not working properly.
I have a 70 c10 CST.

I have 12v on 'both' wires going to the LF signal lamp. Therefore both elements of the lamp are on all the time. The left turn signals don't work. But the right work fine.

I've rewired the LF marker lamp and of course checked the grounds.

I suspect the turn signal switch.

Can anyone suggest anything else to check? Thanks in advance.

Re: Turn signal issue.
 

Is it a steady 12V on Light Blue, or intermittent?

Re: Turn signal issue.
 

Steady 12v on both the LB and BR wires.

Just realized that I haven't disconnected the signal switch. Very dumb mistake.

I'll correct tomorrow and re-test.

Re: Turn signal issue.
 

I have two diagrams with different colors and I'm not sure of either
But I have the same problem on my 70, so I'll be looking at that tomorrow

Re: Turn signal issue.
 

I finally disconnected the turn signal switch and the head light switch wires. And, the two wires to the LF signal are still shorted.
The wires from the head light switch to the firewall are still wrapped in what looks like factory wrap. And the wires from the cowl connector to the core support appear to be wrapped in what looks like factory wrap. Neither appear to have been molested.
The only thing I can think of (at the moment) is to separate the cowl connector to isolate the engine compartment wiring from the wiring under the dash.
The only problem with that is, I'm afraid of screwing up that connector. It's been connected for 55 years. GEE, what could go wrong.
Anyone have another suggestion?

Re: Turn signal issue.
 

It is OK to disconnect that connector. There is a bolt in the middle on the engine compartment side that you loosen, and unplug it. While you're in there, clean up and inspect the contacts. You can unwrap factory-wrapped bundles for inspection of wire, and put the wrapping back on, it is a useful skill and not super difficult. You can get new non-adhesive vinyl tape from Amazon.com and other places, that is what the factory used. They didn't even use zip ties on either end of the wrapping, they just had some sort of nifty knot. On my truck when I unplugged it, I could then pull the wire bundle through the fender where part of it is inaccessible, only to discover rats had sat on the inner fender and chewed the wiring. Having the bundle out of that space and in front of me allowed me to repair and re-wrap and re-install. I used lineman's splce, soldering, and heat-shrink tubing to restore the wires to good shape, they'll be fine for another 50 years. Unless I get a rat...

Re: Turn signal issue.
 

I have a little experience wrapping bundles of wires. Started while I was in the USAF. But then I was using waxed twine. There is a name for it, but I don't remember. Not many on here will know anything about that. The wrap job had to be perfect so it could meet inspection. Ha, ha
I agree with soldering the wires and using heat shrink. But the PO was cool with just twisting the wires together and wrapping that knot with electrical tape. I'm redoing every one of those twist tie's that I can find.
I'll post my findings. But it may be a day or two.

Re: Turn signal issue.
 

^Lacing tape. I've seen miles of that stuff installed, but on spacecraft.

Re: Turn signal issue.
 

I remember those wax-string bundles of wires and having to work on that stuff in the B-52G. Not only did it have to pass QA, but stuff we didn’t touch but could have been noticed by us that was not up to standards of the technical orders was a ding on us if we didn’t catch and correct it ourselves. And by "could have noticed” I mean we better have laid eyes on it during our own inspections. We were using mirrors and flashlights to poke around and inspect everything, because the QA guy was going to come behind us and do that.
So yeah, do that to your truck!

Re: Turn signal issue.
 

Spacecraft and aircraft are different, in that sense. If I had a design or wrote a procedure, nobody ever touched anything that wasn't on the drawing or in the procedure. That was a reason to get written up. Just got more paper written, if there was a problem. Of course, with spacecraft, it's a one-way deal. Can't go back and fix it once it's on orbit.

Re: Turn signal issue.
 

I cracked open the bulkhead connector the other day for perhaps the first time since the first Nixon administration. Daunting, but it was fine.
Good info about the non-adhesive vinyl. I wasn't sure if it had once been electrical tape and lost it's stick or if someone had re-wrapped the bundle with Hefty trash bags

Re: Turn signal issue.
 

The non-adhesive tape is called wiring harness tape. It can be had in various widths. The adhesive on electrical tape degrades and gets nasty.
To set the end of the harness tape just run the end back into a few turns of tape and pull it tight, stretching it a bit.

Re: Turn signal issue.
 

I separated the bulk head connector. Confirmed that my short is not in the engine compartment.
Now I have to trace the wires under the dash. That's gonna be a PITA.

Re: Turn signal issue.
 

...like tying on/tying off a fishing fly ;-)

Re: Turn signal issue.
 

Signal issue resolved.
I separated the bulk head connector 'again' for a closer inspection. Found it was filled with a tar like substance. Looks like factory and I 'assume' it was intended to prevent water from getting to the pins. I decided to clean this substance out so I could see and inspect the pins. As I was cleaning I found a single strand of wire shorting a couple of the pins together. This wire strand was inbedded in the tar like substance, so it was invisible until i removed some of the tar. What a PITA trying to clean that stuff out of the connector. Lacquer Thinner was the only thing I had that would dissolve the stuff.
I reconnected the connector to the fire wall shell. My problem was solved.
I hope my experience helps someone out there with a similar issue.
Thanks for everyone's feedback.

Re: Turn signal issue.
 

Glad you got them working again. Thanks for the insight.

Re: Turn signal issue.
 

Mine didn't have that crap(or not enough for me to notice)
Wonder if someone at the factory ate their Wheaties that morning or some OP had a moisture problem and decided that paving materials were the best solution

Re: Turn signal issue.
 

That kind of an inadvertent connection must be really rare. You're lucky to find it.