I have a 79 f250 2wd. All the lights work (headlights,turn signals, parking lights) except the the tail lights. Fuses are good bulbs are good, I tried to check the wiring for any possible shorts and came up with nothing. I tried searching the forum and the only thing I found was that the brown wire is power. Could that be the culprit? Another thing is I checked the grounds and ended up replacing the ground straps. Still no tail lights. What could be the possible culprit? Any help is appreciated

 

I have read that the taillight bulb housing or socket can cause problems. Also ck the grounds inside the tail light housing area (where the lens goes in the bed).

Head light switch?

Here's what the factory wiring diagram says: for rear lights
Blk/rd= backup lights
Black= side marker, tag lights (on styleside)
Brown=tail lights, tag light (on flareside)
green= RH stop and brake
Yellow/blk= LH stop and brake
Rear light wiring

BROWN: running light circuit
YELLOW with BLACK stripe: driver-side stop/turn
GREEN: passenger-side stop/turn
BLACK with RED stripe: backup lamps

73 & 79 headlight-marker lights use same color codes
Brown= side marker and parking lights
White-blue trace= turn signal
Red-black trace= Low beams
Green-black trace= Hi beams
Black=ground

Flat bed wiring…
Brown= Run Light
Green= Brake light- L
Yellow= Brake Light- R
Black= Reverse Light??
Just wired my front lights. The brown wire is the marker light (side and turn) it is also the top wire on the turn signal socket (three wires in a triangle). The black is ground of course. The white/blue it the turn signal.

 

Automotive Electrical 101 ? Part 1 | Auto Repair Facts

 

Did you check the brake light switch? You didn't say in your post.

 

Thanks 77 and hio for the info that will definitely help and 79ford I did notice the pedal "falls" down a little and it does cause the brake lights to come on when I pull it all the way up the brake lights go off but I still don't have tail lights

The brake light switch works because when I hit the brakes the brake lights come on. Could it still be bad causing the tail lights to not work? How would I check the switch

 

You said "All the lights work (headlights,turn signals, parking lights) except the the taillights."
So I assumed you meant brake lights were the ones not working since I consider parking lights and tail lights the same thing.

For your "tail lights" I would say more than likely you have a bad socket. I've replaced a ton of them.

 

Those sockets can look good....but be bad.

 

The bulbs also have a tendency to wear down the contacts. So.... check your bulbs as well. Also use dielectric grease when you go back together. This keeps the corrosion away and helps with the vibratory wear on those contacts.

 

First question are the rear side marker lights working

If not

Do you have a test light or multimeter if so I can help you narrow it down a lil

At the rear drivers side of the truck near the end of frame rail there should be a square plug.

This is the harness for all the lights for the bed

Unplug this turn lights on and check all 4 prongs on the harness from cab side with the meter or light if one lights up then you are getting power from the cab and now can narrow down to harness to bed side of circuit

Report back

 

There is no excuse these days for not having a multimeter. Harbor Freight provides a coupon for a free multimeter and if ya can't find a coupon, they are still only around $10... that's two Starbucks lattes or three beers from the local watering hole. If in CA, then it's only two beers.

 

The rear side markers do work it's strictly the tail lights that don't. Would the suspect be the sockets? I'll still unplug the rear harness and test it today after work and I'll let you guys know what I find. My beliefs would be that I'm getting power if the rear side markers are working right?

 

I generally start at the actual culprit meaning the taillight bulb and work my way up the line from there.You can check under dashes,midway wiring,rear plugs etc.,but eventually you will probably be checking for 12volts AND ground at the tail light socket itself so I usually begin there. So... my method is to take a test light (the one with the sharp prong and an alligator clip for ground)and with the actual tail light bulb removed,touch the socket contact (the contact that would supposedly give 12v to the bulb)to see if you have current (12v) to this point.Keep in mind this test will only be proper IF you have a GOOD GROUND for the test lights alligator clip. You HAVE to be assured of a GOOD GROUND for any test equipment or you'll be checking all day with no results aside from graying hair! If you have 12v (meaning your test light, lights up) at the bulb contact then put the bulb back in and take a little jumper wire from the good ground you had for the tester and touch the bulbs metal housing if enough of it is showing up and out of the socket.That will give it a proper ground. I'm guessing the bulb will light because of a bad ground,gruddy socket, corrosion etc., which is what other post are telling us. If you have no 12v then work your way to the next in line plug,wiring harness etc. Good luck! Gary

 

since your marker lights work, the issue is isolated to the rear. since your brake lights and turn signals work, you have good ground at the sockets. First confirm the correct dual-filament bulb is installed and as others have said, use a test light or multi-meter starting at the socket checking for power and working your way back to the connector. i've seen many cases where someone hacks into the wiring to add a trailer lights connector and jacks things up.

 

Which I think is the case here I'll try to go through everything today and clean up the wiring as best as I can and hopefully that helps out

Thanks for all the help guys I'll let you know what I find out later today

 

And get pictures of the hack jobs!

Donno why, but love seeing pictures even if it's of hacked crusty rusty fugly undersides