Right Rear Brake Light and Marker Light Out

[Russell J]

Hi Folks! 1972 F100 shortbed here....

Both my right rear brake light and side marker light are not working. They were working previously. The bulbs test good. No lights when I depress the brake pedal or turn on the headlamps. The left rear works fine.

What is the most efficient way of figuring out this issue? I'm guessing I need to test the current in the socket first and move "inward" until I finally get current?

Any direction would be helpful! Thanks!!

[sargentrs]

I would first check all the grounding points on the tail light and marker light housings. Then check at the connector where the wiring harness splits from left to right. http://www.fordification.com/tech/wirin ... _quick.jpg. Does your back up light work? If so, that would imply that the issue is in that split of the harness. Use a test light connected to a good ground and check your sockets in all the connectors to find the break. I had a '74 Dodge Dart whose tail lights gave me fits. Finally found the problem was corrosion in the little dimples where the bulbs locked in. Steel wool on the tip of a screwdriver, cleaned thoroughly and they worked fine. On my '64 Fairlane the driver's side front parking light went dim. Took the housing loose and gave the mounting surfaces a good cleaning and she lit back up nicely. Grounds can go bad with no notice and cause all sorts of gremlins.

[Russell J]

Hey Sarge, thank you for your quick reply!

I just want to make sure that my hypothesis is correct here....If everything on the Left side works, but nothing on the Right is working, the issue MUST be where the lines split off from one another OR just a ground issue or dirty connections on the RIGHT SIDE ONLY.


Does that sound accurate? How far INWARD toward the cab can the fault actually be? I'm thinking no further than where the lines split up in the rear since the left side is getting juice?


Thanks!

[Russell J]

Quick Update....

I have the right marker light working. I removed the bulb, put it back in....and it works...Whatever. Now, on to the right brake light that won't work...

I tried a bunch of different scenarios for the right brake light and here are the results.

Turn Signal = Bulb works
Hazards = Bulb does not work
Headlights/Running Lights = Bulb works
Depress the brake pedal = Bulb does not work

(PS the reverse lights have never been hooked up since I've had the truck but I assure you, the both brake lights were functioning prior to all this)

Any toubleshooting suggestions or where to start would be helpful!!

Thanks!

[sargentrs]

That would be my guess. Somewhere between the left harness to the right harness split. Since removing the marker bulb and putting it back in made that work, I'm leaning toward a grounding issue. Clean out your tail light socket real good with some steel wool. You can wrap it around a screwdriver or drill bit in a cordless drill and spin it around in there, not too fast though. If still not working, try sticking the end of a wire between the bulb and socket and connecting it to a clean ground. Make sure you don't stick it too far down and touch the bottom hot contacts.

[Russell J]

Well, can you beleive that this issue came down to a bad connction in the Turn Signal Switch under the steering wheel?! It's fixed now but, geez.

[sargentrs]

Of course I believe it. It's happened in one way another to every one of us.