1968 GMC Front Turn Signal Issues
 

Hi All...

I'm having an issue with my left front parking light/turn signal. So far I've checked the bulb and cleaned up the ground. Here's what's happening.

With key off and only the parking lights on: Light does not work.
With key off and parking lights/headlights on: Light does not work.
With key on and all lights off: Turn signal works at normal speed but is half as bright.
With key on and only the parking lights on: Turn signal drops to half speed and is still half as bright.
With key on and parking lights/headlights on: Turn signal is still half speed and half as bright.

I am not good at electrical issues so any help and guidance is greatly appreciated.

I have have new wiring harnesses coming for the rear lights because the reverse lights keep blowing fuses and I can't figure out why. I'm assuming the rear lights won't effect the front lights, but maybe they do (?),

Again, thanks for your help!

Re: 1968 GMC Front Turn Signal Issues
 

Check the ground wire on the core support near the voltage regulator. I think there is an additional ground through the housing itself with a screw through a bracket

Re: 1968 GMC Front Turn Signal Issues
 

Taken as a whole, all your "clues" lead to a bad ground.. Check again, you have not cleaned up the ground.. Possibly the bulb socket is loose in the light housing. If you can twist the socket, it's loose and not making a good ground path.. Here's a way to prove you have a bad ground.. Make long jumper using about 10 ft or so wire length. Put a large alligator clip on each end. connect between the bulb socket and NEG battery post.. Try the lights again...

I've repaired several loose socket-to-housing problems.. On the back side, clean and polish a spot where the socket passes through the housing.. Using a 200 watt or stronger soldering gun, heat the metal and flow a "bridge, joining the two pieces..

As for the blowing fuses, that's probably a separate issue.. Just because a harness is new doesn't mean it is perfect, or perfectly installed.. Somewhere in that circuit something is shorted or connected directly to ground... Here is a link to a tool that I have been using for over 50 years for just this purpose.. It has worked for me 100% of the time..

https://www.toolaid.com/product/25100

Re: 1968 GMC Front Turn Signal Issues
 

What is the state of your Turn Signal Switch?
A] Old,
B] New,
C] PO's legacy install,
D] Never been touched by humann hands?

Re: 1968 GMC Front Turn Signal Issues
 

haha I like the multiple choice on the turn signal switch question. I just completed a battle with my turn signals on my GMC. My issues came down to two problems: grounds and turn signal switch. My signals were not working so I went through and checked all my grounds. I found a few that were questionable and cleaned those up. After that, my turn signals still weren't working but the symptoms changed. I went in circles for a while rechecking grounds, bulbs, wires, etc. until I finally decided to pull the wheel off and check the turn signal switch. It was caked up with so much grease and dirt it's a surprise I had any lights at all! After installing a new switch (old one was also cracked and brittle) all is functioning as it should.

Re: 1968 GMC Front Turn Signal Issues
 

The front turn/parking lights are grounded through the housing to the grill . Sounds like a bad ground to me I had one not working and I loosened the mounting bolt and cleans the area and used a star washer worked well after that . The turn signal switch grease tends to dry with age and hampers the contacts

Re: 1968 GMC Front Turn Signal Issues
 

YES, check your signal mechanism in the steering wheel as well!! I had weird front right only intermittent signal issue. Checked all the grounds and still had the issue. Opened up my steering wheel and saw the contacts where all black and dirty. Used some electrical contact cleaner and my signals work perfectly now :metal:

Re: 1968 GMC Front Turn Signal Issues
 

Turn signal switch is original. I took it apart and cleaned up the contacts. Wasn't that dirty. Truck has 54k miles.

Re: 1968 GMC Front Turn Signal Issues
 

Thanks for the advice. I will try the jumper to see what happens.
As far as the backup light fuse blowing, I haven't installed the new harness yet. It's arriving tomorrow.

Re: 1968 GMC Front Turn Signal Issues
 

How is the housing grounded to the grill? Is it the two prongs/studs on each side of the housing that contact the grill when tightened up? The grill was painted this year.

Re: 1968 GMC Front Turn Signal Issues
 

Yup . My right marker was dim and not flashing and the inside indicator was faintly illuminated with the headlamps on the current was looking for ground by back feeding . I had just painted the grill and the inserts prior to assembly . The cleaning and the star washer cured it . I did put dielectric grease on the stud ansd washer to keep it from rusting . I had to do the same with the stepside tailights

Re: 1968 GMC Front Turn Signal Issues
 

I'm sorry..... I mis-read your post about the back up lights.. But before you start running that new harness. Obtain that tool in my link.. I bought mine years ago off one of the tool trucks that made weekly visits to our shop, so I'm not positive where they are available today.. Try places like O'Reilly's or any local automotive parts supplier.. It's easy to use and very effective. You might find that short is easily repaired... Also, look at it from this angle.. What if the short isn't in the harness itself... You've spent all that money and time for nothing.......

Re: 1968 GMC Front Turn Signal Issues
 

I'll look for the tool. Hopefully someplace around me has one. The issue to the rear seems to be the connection where the tail light harness connects the to harness that round to the front. When I wiggle that connection, the first blows. I've disconnected the two and tried cleaning it but it didn't help

Re: 1968 GMC Front Turn Signal Issues
 

So it looks like I had two issues going on. The turn signal housing was not grounding to the grill. Did a little cleanup on the backside of the grill and the turn signal worked properly. However, when I closed my hood, the light went out. Turns out the light socket does not have a good connection to the housing. Need to see if I can fix it or if I need to get a new one. Didn't look like anyone reproduces the original style sockets though.

Re: 1968 GMC Front Turn Signal Issues
 

If you can't find the short finder tool locally, you can order it from Tool Aide, the company in my link..

If you want to solder the socket to the housing, you'll need a really heavy duty soldering gun or iron, at least a 200 watt.. I have a Weller dual range D-550.. Low range is 250 watts, and high range is 325 watts.. It requires that power range it get the metal hot enough for the solder to flow and bond.. I might at, you don't need to solder all the around, a 1/8 - 1/4 inch bridge will work just fine..

I'm not understanding where you say the back up light problem is.. If you're talking about where the harness passes through the firewall, there may be a chaffed area of that gromet that's allowing the wire to touch the metal body.

Re: 1968 GMC Front Turn Signal Issues
 

So it's D] Never been touched by human hands.

Well in 55 years factory plastic or nylon can get brittle and crumble. Mileage is one thing, but age is another.
I had a very weird gripe with my rear lights on a '67 K/10 Suburban, back in the '90s -- before the Internet and this Forum.
I tried new bulbs, CAleaned the ground connections, all the troubleshooting things I'd been trained on as an avionics tech in the Air Wing.
Finally, I put on a new T/S Switch, and, magically, it all worked right.
:chevy:

Re: 1968 GMC Front Turn Signal Issues
 

Not where the harness passes through the firewall. It's the connection at the back, where the taillight harness connects to the harness that runs up to the firewall. The connection is at the last frame cross member at the rear. Something at that connection is blowing the fuses.

Re: 1968 GMC Front Turn Signal Issues
 

I cleaned up the contacts and replaced the springs. The cancelling cam was in good condition.

My issue ended up being the light housing but grounding to the grill and the light socket not seating/connecting properly to the housing.

Re: 1968 GMC Front Turn Signal Issues
 

Yeah, I should check out the passenger side Parking light on my own '71 Jimmy.
It seems to be dimmer than the left one. Now that you bring it to my attention.
Also the Blinking pulse is rapid and weak, rather than slow and strong. The forward Side Marker Lights blink on alternate flashes with the fronts.
Also, on a GMC. the Lenses are rivetted on, so you can't unscrew the yellow lens and get to the bulb frontally. I forgot how.

I need to pull my own wheel, too. The T/S Sw cancelling springs are gone. I have spare kill-springs somewhere. I'm lucky if I can nick the T/S Lever with my pinky when turning the wheel over...
If I miss it, the T/S will blink til I run out of Fluid.

:gmc2:

Re: 1968 GMC Front Turn Signal Issues
 

run a ground strap from the rad support to the frame as well. it cant hurt and the bulbs will most likely get brighter