Headlights flash with turn signals

[jblack6527]

I've searched here, and just on Google for this and can find lots of guys with different problems, but none like this.
If I've missed one, please link me to it.

I have a new to me truck, and when you turn on the Right hand turn signal, everything operates as intended. Regardless whether headlights are on or off.
If you turn on the left signals, with the headlights off, every light on the outside of the truck flashes, including the headlights.
If you turn the signals on with the headlights on, the light on the signal switch comes on steady.

I've been cleaning grounds on the left side of the truck, and have gotten both light housings, and the flasher cleaned but so far have had no luck. I don't get a lot of time to work on it with the rain every day.

I also swapped out the three lever switch, and flasher with known good(new) parts to no success.

Does it sound like I'm on the right track? Any other ideas?
I have a multimeter but other than checking for voltage I'm not very handy with it.

 

[frank8003]

inside left front fender is #69 and #96 reversed?
Do you have that PDF?
But all the lights actually illuminate when it "happens" with the left signal?
Were the police working on it?

 

[cattlerepairman]

What Frank said! Something is feeding power to where it shouldn't go.

Sent from my SM-G950W using Tapatalk

 

[Mullaney]

I've searched here, and just on Google for this and can find lots of guys with different problems, but none like this.
If I've missed one, please link me to it.

I have a new to me truck, and when you turn on the Right hand turn signal, everything operates as intended. Regardless whether headlights are on or off.
If you turn on the left signals, with the headlights off, every light on the outside of the truck flashes, including the headlights.
If you turn the signals on with the headlights on, the light on the signal switch comes on steady.

I've been cleaning grounds on the left side of the truck, and have gotten both light housings, and the flasher cleaned but so far have had no luck. I don't get a lot of time to work on it with the rain every day.

I also swapped out the three lever switch, and flasher with known good(new) parts to no success.

Does it sound like I'm on the right track? Any other ideas?
I have a multimeter but other than checking for voltage I'm not very handy with it.

Either that or a really bad ground. It might me worth a 20ft piece of 14ga wire with an alligator clip on each end. Clip one end to the ground on the battery and the other to a known good ground INSIDE the turn signal on the brass base for the bulb. If the problem suddenly disappears - you know the ground on the fender isn't (grounded properly).

 

[Mullaney]

inside left front fender is #69 and #96 reversed?
Do you have that PDF?
But all the lights actually illuminate when it "happens" with the left signal?
Were the police working on it?

Frank,

Is there any chance that you have a drawing like that for the electrical on a 939 Series (936 in particular) truck? Or maybe a CAD drawing of the hydraulic plumbing on that same truck?

 

[Barrman]

Really, really, really check all the grounds for the blinkers on that side of the truck. Start with the screws into the blinker buckets, maybe even pull the lens covers off and make sure the ground wires inside the blinker bucket are connected and clean.

 

[jblack6527]

inside left front fender is #69 and #96 reversed?
Do you have that PDF?
But all the lights actually illuminate when it "happens" with the left signal?
Were the police working on it?

I do have that PDF, but what are you referring to as #69 and #96? I'm not seeing them in the PDF?

And yes, lights actually illuminate. I figured it out seeing the reflection and funny looks from the car in front of me a couple days ago.
Bought it from and individual, so who knows who was working on it. haha

 

[jblack6527]

Either that or a really bad ground. It might me worth a 20ft piece of 14ga wire with an alligator clip on each end. Clip one end to the ground on the battery and the other to a known good ground INSIDE the turn signal on the brass base for the bulb. If the problem suddenly disappears - you know the ground on the fender isn't (grounded properly).

This is a good idea, I'll pick up a couple of alligator clips and make one of those up.

Really, really, really check all the grounds for the blinkers on that side of the truck. Start with the screws into the blinker buckets, maybe even pull the lens covers off and make sure the ground wires inside the blinker bucket are connected and clean.

I've done this, cleaned and ran the screws through a thread die, and a tap into the bucket threads. Wire brushed the brackets the lights bolt to and put a little grease on the threads and washers.

The inside of the lights looked pretty clean, I'll double check.

 

[glcaines]

I would ask the guy you bought it from if he had the issue and ask him who was working on it and what they were working on.

 

[frank8003]

I do have that PDF, but what are you referring to as #69 and #96? I'm not seeing them in the PDF?

And yes, lights actually illuminate. I figured it out seeing the reflection and funny looks from the car in front of me a couple days ago.
Bought it from and individual, so who knows who was working on it. haha

My my '69 jeep kaiser M35A2 I had removed left front fender to do work. The wires did in fact have 69 and the other 96 which I reattached wrong when reinstalling. Was like upside down and backwards working, no excuse. Also the right front headlight normal low beam was burnt out and I could never get the blackout lamps to work. This created various more dumb moves leading me down the wrong paths. I got a photo someplace, take me weeks to find it. Yes, it is original wiring harness. You are correct in what I found is not on the PDF. Working on all that is what led me to get the PDF diagrams in the first place.

 

[Mullaney]

This is a good idea, I'll pick up a couple of alligator clips and make one of those up.



I've done this, cleaned and ran the screws through a thread die, and a tap into the bucket threads. Wire brushed the brackets the lights bolt to and put a little grease on the threads and washers.

The inside of the lights looked pretty clean, I'll double check.

And if you want to go "on the cheap" alligator clips could be optional. I just like to use them because if things go bad - you can yank the wire - and immediately undo what you added to the circuit.

Long years ago, company I worked for would buy F750's with just the cab. We would convoy the trucks back from the dealership to our shop. Our job was to install "line bodies" and then attach whatever lifting device (people or equipment) inside that body and attach it to the frame. We had a one inch thick piece of very dense wood that went between the frame rails and the bottom of the bed. My first wiring experience on that project was installing the marker and tail lights. Drill holes, bolt on lights, attach wires... Then connect everything to a central point in the truck wiring harness.

NOTHING WORKED. Turned on the turn signals and they were spastic. I don't remember them making the headlights blink - but every light on the bed would do a "shaky" blink/flash with the 4-way flashers turned on. I picked up a battery jumper cable and clamped it to a marker light (they were all metal in those days). Then hooked the other end of the jumper cable to the truck frame - and there was a spark - but the lights started working correctly. Turned out that I had missed the "ground to frame" connection in my hurry to see all the lights come on

 

[jblack6527]

And if you want to go "on the cheap" alligator clips could be optional. I just like to use them because if things go bad - you can yank the wire - and immediately undo what you added to the circuit.

Long years ago, company I worked for would buy F750's with just the cab. We would convoy the trucks back from the dealership to our shop. Our job was to install "line bodies" and then attach whatever lifting device (people or equipment) inside that body and attach it to the frame. We had a one inch thick piece of very dense wood that went between the frame rails and the bottom of the bed. My first wiring experience on that project was installing the marker and tail lights. Drill holes, bolt on lights, attach wires... Then connect everything to a central point in the truck wiring harness.

NOTHING WORKED. Turned on the turn signals and they were spastic. I don't remember them making the headlights blink - but every light on the bed would do a "shaky" blink/flash with the 4-way flashers turned on. I picked up a battery jumper cable and clamped it to a marker light (they were all metal in those days). Then hooked the other end of the jumper cable to the truck frame - and there was a spark - but the lights started working correctly. Turned out that I had missed the "ground to frame" connection in my hurry to see all the lights come on

That's a great story. Goes to show no matter how often you do something, there's always room for "hurry up" error.

I tried the ground cable idea with a set of jumper cables and the short alligator clip lead I had on hand. No change.

 

[Jbulach]

Try pulling the turn bulbs out one at a time and see if the feedback problem fixes itself with either bulb out. If so make sure it is the correct bulb and is oriented in the socket correctly.

 

[jblack6527]

Try pulling the turn bulbs out one at a time and see if the feedback problem fixes itself with either bulb out. If so make sure it is the correct bulb and is oriented in the socket correctly.

I didn't pull them one at a time, but tried it with no bulbs at all and it was the same way.