Brake & turn signal light issue

[JDHollis]

I am looking for ideas on solving issues with me brake and turn signal lights. My 78 C10 has no brake lights and when you turn on turn signals the front lamps work as they should. But, both rear lights “blink” with either the right or left side selection.
I have changed the turn signal switch in the column and the brake light switch. I have also unplugged the tail light harness, at the bulk head, checked with a test light, and the test light indicates exactly what the tail lights are.
Thoughts or ideas????

 

[Charlie]

 

[richard A lindner]

Check your groundwires

 

[norman baker]

LOOK FOR BAD GROUND IN REAR ? OR CLEAN A PLACE ON THE FRAME NEAR THE LIGHTS , USE NUMBER 12 WIRE TO THE GROUND ON EITHER LIGHT THEN TRY BLINKERS AGAIN. CHECK BRAKE LIGHT SWITCH ALSO ?

 

[73c20jim]

Cap lock broke???

 

[Donald]

This may sound dumb but check your bulbs , if you have a single contact bulb in a socket that is for a double contact . It will cause back feed problems like what you are getting . Don

 

[MikeB]

Are you saying that with the brake pedal depressed you measure battery voltage on the appropriate bulkhead connector?

As for testing the turn signals that way, I think you may need to have bulbs in the circuit to draw current thru the flasher (that causes it to flash), so I would not expect to see "blinking" on the firewall connectors.

Have you replaced the turn signal flasher? How about the hazard flasher? On my 82 C10, brake and tail lights work fine with the hazard flasher removed. And I think the flashers are interchangeable.

This is some basic stuff, but I want to mention it anyway: Does your 78 truck have a single 1157 bulb dual-filament per side? If so, that means one filament is used for tail lights, the other for brake AND stop lights. Then of course there's a separate backup light bulb.

 

[elcamman50]

I had almost the same problem on my 79, Big Ten. After troubleshooting everything you did, I found the problem in the harness connector on the right side of the steering column under the dash. It is the long one with numerous wires coming from it. It connects the wiring from the upper steering column, blinkers and brake lights, to the brake and light harness. Found the green wire, on the bottom part of the harness, it splits into two pieces, top and bottom, had broken but still looked like it was intact. Went to a Pick A Part and found a good bottom part of the harness and spliced it in. Now all my blinkers and brake lights work again. Hope this helps.

 

[JDHollis]

This may sound dumb but check your bulbs , if you have a single contact bulb in a socket that is for a double contact . It will cause back feed problems like what you are getting . Don

 

[JDHollis]

Thanks Donald. Bulbs are all good. This problem started out of the blue. Everything thing was working fine. I ran an errand in the truck and was gone about 15 minutes. When I got home, my wife noticed the the brake lights weren’t working. I have since got the brake lights back but still haven’t figured out the turn signal issue.

 

[JDHollis]

This may sound dumb but check your bulbs , if you have a single contact bulb in a socket that is for a double contact . It will cause back feed problems like what you are getting . Don

 

[JDHollis]

Thanks Donald. All of this started just out of the blue! Ran a short errand in the truck and when I got back home my wife noticed the brake lights not working. The bulbs were the same ones that were in the truck before. The bulbs test good and both filaments are intact.
I have since got the brake lights back but still haven’t solved the turn signal issue. I appreciate all thoughts and ideas though!

 

[JDHollis]

Are you saying that with the brake pedal depressed you measure battery voltage on the appropriate bulkhead connector?

As for testing the turn signals that way, I think you may need to have bulbs in the circuit to draw current thru the flasher (that causes it to flash), so I would not expect to see "blinking" on the firewall connectors.

Have you replaced the turn signal flasher? How about the hazard flasher? On my 82 C10, brake and tail lights work fine with the hazard flasher removed. And I think the flashers are interchangeable.

This is some basic stuff, but I want to mention it anyway: Does your 78 truck have a single 1157 bulb dual-filament per side? If so, that means one filament is used for tail lights, the other for brake AND stop lights. Then of course there's a separate backup light bulb.

 

[JDHollis]

1. I’ve got the brake lights back working. I repaired a broken ground between the frame and the bed, just behind the cab and replaced the brake light switch.

2. I have not replaced the flasher but I did swap the two, one for the hazard and one for the turn signals. Nothing changed there.

3. It does have the single 1157 bulb. Both filaments are good as indicated by brake lights back working.

Turn signals are still not working correctly. Both rear lights “blink” regardless of which side is selected. Front signals operate as they should.

 

[roundhouse]

Could be the signal switch itself

But you need to start by checking the wires under the dash

Find the wire coming down the steering column for the right and left turn

And see if they work as they should there
Then check on the inside and outside of the bulkhead firewall connector

I had power on the inside of the big connector but not on the firewall side

I also had a bad switch behind the steering wheel
The one that’s operated by the lever