Have a 78 F-150 - all the lights work OK except the rear turn signals and brakelights. Headlights and front turnsignals are fine as are the taillights. Just no left or right turn or fourways in the rear and no brakelights. Didn't find any blown fuses and installed new bulbs. I guess its a wiring issue but just wondering if anyone has experienced the same or knows of a likely source for me to look first - I hate tracking down wires especially on vehicles... Thanks.

 

Hook up a wire for a temporary ground and see if this corrects the problem.

 

it might be your brake light switch

 

Check the turn/brake wire contact in the bulb socket with either a test light or VOM to see if voltage is getting back there - if so, the socket may need replaced. If not, continue upstream until you find voltage. May be a break in the wire somewhere. Also check the connectors along the path - might be corrosion on the terminals. There will be one under the bed somewhere to facilitate bed removal. Could also be in the turn signal switch or headlight switch, too.

 

I myself would be testing the turn and hazard switch assembly in the steering column itself as everything in the rear is wired through this switch except the tailights. Its usually the the hazard switch that goes in such assemblies.

 

Thanks for the replies - I didn't think it would be the hazard or brake light switch since the hazards work in front - and they don't work in the rear so I wouldn't think its the brake switch. The brakes/turns use the same bulb filament and wire correct? I doubt both bulb sockets are bad especially if they both have the exact same problem at the same time but I will check these things out. Just like I figured both bulbs were doubtful to be bad at the same time but it was the cheapest and easiest place to start. Thanks again for all the help so far. I'll keep digging.

 

The Hazard lights work in the front but not the rear?

Then it's not the fuse. Hazard and brake lamps use the same fuse.

With the hazard lamps on check for power at the Yellow/Black and Green wires at the steering column connector.

Circut #283 Yellow/Black wire Rear Left Side Turn Signal and Brake lamp.

Circut # 282 Green Wire, Right side Rear turn signal and stop lamp.

If no power at the steering column connection with hazzard switch on, with front lamps working, turn signal switch is suspected fault.

 

The wires under your truck are near 30 years old. Every time you run through a pot hole, the wires flex. To make matters worse, the clips that hold the wires along the frame wear into the wire's insulation. This in mind, remove a bulb from the rear, and check for voltage with a volt meter or test light. All the advice given above is sound by the most part. Your problem could also be in the headlight switch. Good luck.

 

When the hazard flashers are on you may have noticed that the turn signals may not have worked correctly and the brake lights as well or they would have over riden the hazards in the tail. Also when u turn on signal it overrides the brake light on that side. All of this indicates that the rear lights work thru the hazard and turn signal assembly. I would start there. Believe me about the switch as I rewired this entire truck and this was the part that gave me the most challenge.

 

i just fixed the same problem on my 76 turns out that the plug in the back under the bed by the frame had been cut and bypassed on some of the wires and the remaining ones were coroded bad so we put a bunch of spade connectors on the wires since the wires that were cut had been cut right at the plug so we couldnt splice them only took 15 minutes then they worked fine i would check that plug you never know what kind of shape stuff is in when you buy a truck this old

 

The 4 way flasher switch (hazard switch) comes as part of the turn signal switch.

1978/79 F100/350: There are three different turn signal switches (same as '78/79 Bronco & Econoline).

All three are still available from Ford.

D8TZ13341A .. T/S Switch ~ Use with Tilt Wheel

MSRP: $136.00 / ftepartsguy.com price: $97.92
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D8TZ13341B .. T/S Switch ~ Use with A/T-Fixed Wheel

MSRP: $110.00 / ftepartsguy.com price: $79.20
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D8TZ13341C .. T/S Switch ~ Use with M/T-Fixed Wheel

MSRP: $105.98 / ftepartsguy.com price: $76.31

 

have you made sure the connectors are clean and tight? when my brake lights stopped working i pulled apart all the connectors, cleaned them and put on some goop my dad had laying around ( cant remember what it was). didnt fix the problem, but the truck really needed it.

 

Should eliminate the turn signal switch before going towards the wiring in the back. If the turn signal switch tests ok, then he needs to follow the frame harness to the next plug connector. and test again. This eliminates sections in the proper order to isolate the problem quicker.

The odds, of both turn signal and stop lamps not working on both sides, because of wiring is lower than if it is the turn signal switch itself. Why you start at the front and work back.

Now if one side or the other worked, but not the other, then you start at the back and move forward.

It's not the headlamp switch. The headlamp switch is not connected to the Stop, or turn signal lamps at all. So the headlamp switch is not involved in this.

 

It does...

All the rear lights except the parking (Tail lamps) and the back up lights goes through the turn signal switch.

There are little metal prongs inside the switch that make the various connections for the wires, if one of these breaks off, then it can cause a problem like is being described here.

 

Yes I should have specified except tail and backup.