Tail lights and signals going whacko.

[mike's1965]

Truck has been parked for years, trying to get it back on road, my biggest issue now is turn signals not working, this was not a problem before parking truck.

Trying to get it from my mom's to my place, but can't until the tail lights, signals work properly.

Turn on left signal, both rear signals flashing, I think right signal makes left signal flash too.

Took off uhaul trailer wiring harness that had been on 15 years, cut back some wires to get fresh wires, anyways after taking that out and hooking the wires back up, it's still doing this.

Also driver's side front blinker not working, bulb fine, also front parking lights not working when switch pulled out one click.

Could a bad bulb cause any of this?

Any ideas what to check next time I come over?

[REDROCKER652002]

Have you checked the flasher at the fuse block? Probably not that, but it is easy and quick to change out. What about a possibility that the wires are crossed somewhere between the plug and the tail lights? Or maybe frayed and they are touching? Not really an expert, so I will let the ones who know chime in. Good luck, maybe a ground issue? that seems to fix a lot of issues with electrical.

[The Rocknrod]

Without being there to look I'd have to ask have you looked at the grounds in various places on your truck. Percentage wise it's usually the grounds that went bad.

[werito1]

had same problem a few months ago. I ran a pair of ground wires from rear bumper bolts to bed panels behind tail lite housing. that solved the problem.

[rustyrodknocker]

Typical issues from sitting are bulbs not working at all or intermittently working.
This will be from breaks in continuity. Check you bulb sockets with a test light.
Check before and after any splice. Clean sockets, fuse holders and connectors with something like scotchbrite.

When blinkers or flashers are malfunctioning, as in lighting up when not switched on. This is to that circuit bening energized when the signal lever is not in that position. Meaning an unwanted reroute within the switch. The turn signal switch is both the mechanical and electrical hub of signal lights. Some times they are cleanable or repairable but often the connection is toast with made rivet connections or the 60 year old plastic is done for.

In my experience when they don't auto cancel. The plastic associated with the canceling cam is broken.
Its hardly worth fiddling with a 60 year old signal switch. If their not broken they will be soon.

If I remember correctly the GMC's have a different switch, do to some having only one indicator in the dash. Keep that in mind if thats what you have.

[mike's1965]

I will try flasher next time and look at grounds.

Did this in the dark to see the lights better, they are so week it's hard to tell in daylight.

Forgot to mention couple months ago I put on new battery cables, thickest ones I could get, also side post, using battery out of C5 Corvette that is 1000 cranking Amps, and I think 800 cold, it's a good battery but it got wrongly diagnosed at O'Reilly as bad so I kept it since it's AC Delco and I payed some decent $ for it, and bought a new battery at Costco for the Corvette.

By the way I had a feeling the battery was good.

Turns out buying a trickle charger ( started researching battery on cars how to restore, maintain etc)and charging it for a few days at a time in garage by itself, then about a year later I took it to O'Reilly and had it tested, told me it was in perfect shape, don't let them test a battery that is slightly discharged with their fancy battery machine.

Back to putting in battery and new #2 guage battery cables, truck cranked up so much better, starter cranked faster and stronger, before I was using this battery with charging adapter things that screw into the side post threads, and then pushing the old clamp type cables over the charging adapters, the old battery cables I put on in late 1996 or early 1997 after the hot cable melted on header tube and shorted out, noticed those were #6 guage.

That evening couple of months back after putting in new thick side mount cables like I said it started so much easier, also turned on headlights while truck was running, seemed brighter, then tried brights by clicking floor switch, just letting truck run, was doing something else in backyard, after a few minutes I noticed headlights out, I figured my brother turned them off but they were on, turns out they only worked on brights.

Came over next week same thing, after messing around testing stuff and pulling connecter out at firewall and putting back in the headlights again worked on low and high.

There are ferral cats taking over that neighborhood and they get under the hood, see paw prints in the dust on engine, I wonder if the cats messed up wiring.

Maybe they chewed wires, or something.

Will check flasher, headlight switch, look for grounds.

Anyone have wiring diagram for 1965 C10 for lights?

[mike's1965]

Originally Posted by rustyrodknocker

Typical issues from sitting are bulbs not working at all or intermittently working.
This will be from breaks in continuity. Check you bulb sockets with a test light.
Check before and after any splice. Clean sockets, fuse holders and connectors with something like scotchbrite.

When blinkers or flashers are malfunctioning, as in lighting up when not switched on. This is to that circuit bening energized when the signal lever is not in that position. Meaning an unwanted reroute within the switch. The turn signal switch is both the mechanical and electrical hub of signal lights. Some times they are cleanable or repairable but often the connection is toast with made rivet connections or the 60 year old plastic is done for.

In my experience when they don't auto cancel. The plastic associated with the canceling cam is broken.
Its hardly worth fiddling with a 60 year old signal switch. If their not broken they will be soon.

If I remember correctly the GMC's have a different switch, do to some having only one indicator in the dash. Keep that in mind if thats what you have.

Replaced turn signal switch in early 2000 bought from some Chevy truck place in Oklahoma I had catalog for, it was almost $100.00 with shipping then, reason for replacing was I had to sometimes turn signal off myself after making turn.

The new switch was same way and I was disappointed, figured that must just be the way old trucks were, meaning it works most of the time, but sometimes needs help turning off.

Never worked like newer vehicles.

Will check the turn signal switch, 20 years is old too. Lol

[mike's1965]

Update, bought new turn signal switch, flasher, and some electrical connectors at AutoZone.

Left my turn signal switch mounted, never pulled steering wheel or anything, unplugged the 2 harness connections, plugged in new turn signal harness connections, same.

So no tail lights or parking lights on front, turn signal switched to right, old or new switch, front blinker works, both rear blinkers flash like hazard lights.

Switch to left old or new switch, no front blinker, both rear blinkers flash like hazards.

Brake lights work.

Thinking it's time to replace harness or harnesses for rear lights, found some brittle wires, also other people at one time have spliced into it, I cut out lots of splices and got fresh wires twisted together using wire nuts just to test.

Never tried flasher.

Don't think it's a bad ground since brake lights work.

I can try flasher if others think it might help.

Forgot to check headlight switch.

I'm thinking it's the wiring harness, 55 years old.

Fuses looked ok, pulled tail light fuse and broke it, one metal end separated from glass tube, probably just grabbed it wrong, popped one side out and pulled and it separated, guess you have to try to pry both sides out, or maybe it was just fragile from old age.

Any other thoughts or ideas?

[MikeN]

I'd still be suspicious of bad grounds. Bad grounds lead to wacky symptoms. Harnesses are expensive - I might at least experiment with an extra ground wire as described above before spending money.

[mike's1965]

New update, held off on buying any taillight wiring harness, came back to truck to do more testing.

Now the instrument panel light or dome light is not working, it was before, I did pull fuse last week for taillight slot and it was hard to come out, in fact it separated while I pulled it out.

Fuse holder clips look kinda rusty or rough, so before putting in new fuse, squirted some WD-40 on old toothbrush and brushed the holder clips.

Went to AutoZone and bought a new headlight switch, no change but I think maybe the fuse panel is suspect.

Using a test light to double check fuse I just replaced, see spark near fuse end and fuse holder, and instrument light lit up, if I turn switch off and in to parking lights again, spark and instrument light comes back on.

Still no tail lights, and now front passenger side blinker not working.

Should I pull out the fuse panel?

This was first fuse I've replaced in almost 25 years of having truck that I recall.

I'm going to see if there are replacement fuse panels, maybe update to the kind that uses blade fuses if possible?

[mike's1965]

I explained that wrong, after spark from probing fuse and fuse holder and instrument panel lights up, if I turn off headlight switch, and pull out one pull for parking lights, no instrument light anymore, unless I probe fuse with test light.

Fuse appears to be pushed in all the way, thinking it's crusty or corroded fuse holder clips.

[cwcarpenter98]

On my 63, the brake lights and windshield wipers did not work when I first got the truck. The connection points in the back of my fuse block got rusty. I was able to move the plugs around from the back side on both the taillight circuit and the windshield wiper circuit to make both circuits work. One day, the fuse blew on the wiper circuit so I decided to replace the fuse block. I got one that looks and functions exactly like the factory one. It has worked great and I have not had any issues with the brake lights, turn signals, and wipers since

[mike's1965]

I pulled fuse out and put it back in and instrument panel light and dome light working again, glad that's working.

Digging in deep in tail light sockets, trying to add ground wires, while messing with all this, I just looked up LED tail lights for 1965 C10.

Does anyone run LED?

If the stock stuff is bright enough I guess there is no need.

Man I never imagine lights on a old truck would be so tough.

[0ldSoul]

I was having a similar issue where the left or right turn signals would function as emergency lights. In my case, the previous owner had butchered the rear wiring harness pretty bad so I ordered a new harness from the firewall to the rear frame, and from the rear frame to the tail lights; got them from Classic Industries.

I also ordered new taillamp housing mounting clips from Classic Parts of America. Those are important because it's how the factory designed the tail lights to make ground.

Since Classic Industries was taking a bit to ship out, I decided to add a ground wire directly from the tail light mounting clip to a hole already at the rear of the frame.

Once I got the wiring harness installed, tail lights function perfectly. Wish I could tell you if it was the ground or the harness! If you need a picture of the ground wire at the tail light, let me know but it's just a fork terminal slid into the tail light mounting clip with the wire going down the same direction as the harness and bolted to a hole already at the rear frame.

Wiring harness from firewall to rear frame:
https://www.classicindustries.com/pr...9945.htmliring

Wiring harness from rear frame to tail lights:
https://www.classicindustries.com/pr...s/ct30845.html

Tail light housing mounting clips:
https://www.classicparts.com/1958-66...ctinfo/49-031/

[mike's1965]

I went over again at sunset, weather went from very nice to hot quick, even after dark still hot.

Anyways this time I came with a plan and a cordless drill, first I decided to start at firewall and use a test light where the front turn signals and parking lights plug in, each one worked, parking light output, and both turn signal outputs.

Plug harness back in and tried parking lights again, still nothing, so drilled a self tapping screw into the passenger side signal/parking light housing, used jumper test wires to add ground from battery negative to the screw, nothing.

Started testing socket where bulb touches, nothing, so started poking in wires outside but near socket, nothing. Unplugged harness and double checked still getting output there and it was.

I decided that if the front harness looks 10 times better and is not brittle and breaking, no splices, and it isn't getting voltage to lights and needs replacing, the rear harness which has so much more trouble must be bad too.

If there are problems after replacing all 3 harnesses, front harness, and 2 harnesses for rear lights from firewall to back harness, and harness for taillight, well I'll go from there.

[0ldSoul]

I hope it solves your problem. If you order from Classic Industries, be patient; they're getting caught up from closing their warehouse due to the pandemic.

When I placed my order, it took about a solid week before it even shipped out.

Once I got confirmation that it shipped, it arrived very quickly.

Wish you luck, let us know if it fixes your issue.

[mike's1965]

Originally Posted by 0ldSoul

I hope it solves your problem. If you order from Classic Industries, be patient; they're getting caught up from closing their warehouse due to the pandemic.

When I placed my order, it took about a solid week before it even shipped out.

Once I got confirmation that it shipped, it arrived very quickly.

Wish you luck, let us know if it fixes your issue.

I am ordering from Classic something in Kansas, used to be Chevy Duty years ago, I hope it works too, have lots of things to do on the truck, add EFI next, then if that works out, I'm going to try out a cheap A/C underdash kit I see on Amazon for 250 bucks including compressor, underdash unit, condenser, and hoses and fittings, will need tool to crimp but that's ok, just need to make sure it's sanden style compressor, vintage air makes a bracket that fits BBC on driver's side.

I'm holding off on buying the A/C kit just yet, don't want to bite off more than I can chew, the pro flo 4 sounds easy, but from reading others on that forum it may take lots of work to get it dialed in.

Then truck needs new tires, and might as well buy GM chrome rally wheels, plus need overdrive haha. $$$$

[lowroder]

just had a issue with my rear taillights as well.. previous owner started to install LED markers an taillights..
lights were very dim an intermediate... bought new taillight harness from classic parts /eklers an also got new tail light buckets..
once recieved i made new ground wires from housing to frame rail..
plugged in new harness an had very very brite lights..but however the tail light functions was off... had tail an brake but turn signals flashed like hazrds..
after testing many things.. it was a bad plug from the harness i purchased.
cut off plug an rewired my original. an my taillights work perfectly...
maybe check grounds yes.. but also check rear harness plug at frame..
just a FYI might help

[mike's1965]

So the new harness that was bad was bought from the place that used to be called Chevy Duty, or Ecklers?

The last thing I want to do is have to fix brand new stuff, I need to see if there is at least a warranty, still have not ordered.

[0ldSoul]

The harnesses I bought from Classic Industries can't get any better in terms of quality and work flawlessly. The brand is American Autowire which is American made and is the go-to for many classic car restorers.

[lowroder]

Originally Posted by mike's1965

So the new harness that was bad was bought from the place that used to be called Chevy Duty, or Ecklers?

The last thing I want to do is have to fix brand new stuff, I need to see if there is at least a warranty, still have not ordered.

yes was bad plug on new harness from Ecklers.. Made by american autowire .
i cut off the new harness plug an resolder my old plug an...walla Fixed

[mike's1965]

I ordered from Classic Parts earlier today, not sure who makes the harnesses but need to get that truck moved from San Tan Valley Arizona to Chandler after fixing turn signal/taillight issues.

Then can get started on fuel injection swap.

[lowroder]

Probably American autowire. They make everyone harness I believe.
Like brothers, lmc, classic parts etc.
Not saying there a bad company.
But mine was defective.
So still would like a discount or something for my trouble.
I bought new for a reason.

[mike's1965]

Is that the connection from front section of taillight harness that plugs into rear section of taillight harness?

Sounds like it had a short, or maybe wires got put in wrong terminals.

[lowroder]

Yes...
Plug from taillight harness.
When I spoke to America about it.
They said based on my tests...
They said they believe plug issue as previously diagnosed.
Only way to confirm was to cut it..
So something in manufacturing got crossed