So I have a1968. My question is why don’t I have brake or reverse lights. My turn signals work fine on both sides. I know the true signal switch controls the brake lights. But like I said they work fine. I have no clue about the reverse lights. Any idea what it could be ?

 

For the brake lights make sure your brake light stop switch (located on the pedal) is working and connected. Otherwise I would trace wires and verify that all bulbs are good. I know at least for the turn signal, the system will short itself out if not all the bulbs are good.

 

The brake lamp switch attaches to the brake pedal and can be adjusted. There's a retainer that attaches to the pedal that the switch threads into.

The clips on the retainer snap off, the switch doesn't fit properly, or falls off, suspended to the pedal by its wire harness.

The retainer (C8TZ-13A629-A) is obsolete, but has been reproduced, it's also available NOS

If your truck has A/T, the backup lamps work via the NSS (Neutral Safety Switch). The switch is the same 1967/77 F100/350.

If a 3 M/T, the backup lamp switch is located on the steering column under the hood. If a 4 speed, the backup lamp switch threads into the shift tower.

The usual cause of no brake or backup lamps are bad grounds. The bulb sockets get dirty, use a pencil eraser to clean them.

 

2X Bill. Also check both switches and make sure their wires are hooked up.

 

I hope this thread isn't too old to revive...

I'm having a similar problem, but it's just my reverse lights. Brake lights, turn signals, everything else works. I have a 1968 with the 240, 3 M/T. New alternator, new voltage regulator. I replaced the backup lamp switch at the steering column, and am seeing 11.6 volts at the switch with the engine idling.

My question is: What's the voltage I should expect to see at the bulb sockets for the backup lights?

 

In a perfect world, the same as at the switch. But with that much length of old wiring and probably a connector or two involved, it could be more than a volt less.
No matter where you look and on whatever circuit, you want to keep voltage drop to an absolute minimum to keep everything happy and working properly. Too much drop at the backup lamp sockets and they might still work, but will not be as bright as they could otherwise be.

Speaking of 11.6v with the engine running, what is it reading at the battery terminals? And what, if any increase do you see when you rev the engine up a little bit? The 11.6v way up at the switch, which is still near the battery and charging system, is a bit low for my liking already. But with the engine just idling maybe your alternator is not putting much out like it would be at a higher rpm level.

Back to the lamps, on some older trucks with this style lens and reflector, the backup lamps are a separate item from the tail lamps (same housing, but insulated) and have their own ground wire that goes to the body. If rust and/or paint are an issue, or if the wire and connector are compromised, the other lamps might work fine but the backup lamps still won't.
I know for Broncos, the '66 model year did not even have backup lamps and the tail light lens was entirely red. Later in the year Ford added the backup lamps by cobbling together a secondary housing and socket. Hence the separate ground wire, where the other lamps get their ground through the housing to the bed metal.

How do the rest of the systems work? With old trucks the main battery ground to the body is often removed without even thinking about it. And given the age of these trucks now too, rust and overspray have their way with ground paths as well. So it never hurts to make sure that, in addition to your main ground cable to the engine block, you also have a secondary ground wire from the battery to the body on the fender nearby. Then if your truck does not have, or never had, a ground strap between the engine and the firewall, now's a good time to add one yourself. Along with a small ground to the frame and then another one that you add from the bed sheet metal to the frame, all go a long way towards a happy electrical system.
Ford relied a lot on metal-to-metal contact for ground bonds back then. That was great when the trucks were new, but add 50+ years to that fact and many of our electrical gremlins can be traced to poor grounding.

Sorry for the long-winded dissertation, but so many of our trucks lose their grounds over the years i thought I'd just give you more crap to look out for!
Oh, and I forgot to mention dual exhaust! If you have, or your truck ever had dual exhaust you absolutely need to check the entire run of wire along the driver's frame rail to make sure it's not crimped, crudded up, or melted where the exhaust got too close.
Just one more thing to check when you get a new-to-you old truck.

Good luck.

Paul

 

I FOUND THIS YEARS AGO..............
DO NOT REMEMBER WHERE & IS STRANGE..................BRAKE, TURN, EMERGENCY LIGHTS SHARE THE SAME LAMP FILAMENT
This info may not b accurate..........If u r turning & mash brake pedal, what happens then.............
ANY thoughts ???????........

 

Your information is correct as far as our trucks are concerned. Others that use for example amber turn signals would be a different bulb. But ours that are all red use stop/turn/hazard on the same filament and same wire all the way up to the turn signal switch.
In this case though the latest question from Mattress a few days ago was only regarding a problem with the backup lamps. So in this case, a separate circuit and bulb.

But for questions about brake lamps, yes it's true that all three work on the same circuit. All the magic happens at the turn signal switch.
Along with most of the problems too!

Paul

 

Thanks Paul for the essay! I appreciate all the info. You were absolutely right; it was a bad ground at the backup lamp housings (both sides). There was just enough oxidation between the backup lamp housing and the rivets that hold it onto the main tail light housing that prevented closing the circuit for the backup lamps, but the connection for the brake/turn lamps was fine. Seems like the backup lights were simply added on to the existing tail light housing design. Along the way I cleaned up other connectors and grounds and now I have ~13.6v at the backup lamp switch at idle, and about 12.5v at the lamp sockets. My alternator is giving me 14.3v, so there's still a sizeable loss from the battery to the switch, but the lights are plenty bright! Maybe I'll add my own ground wire to those housings later... The truck has been in the family since new and has had very little modification, which has been a blessing while troubleshooting.

Also, RTT: I found that activating the turn signal with the brakes applied caused the lamp to behave only as a turn signal, but if the running lights were turned on, those of course stayed lit since that's a separate filament.

 

It’s starts in neutral with no issues. Never started in park. I replaced the bulbs for the reverse lights and they were a bit dirty and corroded. One bulb was stuck and I had to pry out with a pair pliers. Gonna try and clean the sockets and by a new brake light switch.

 

My turn signals work fine. Still no brake or reverse lights. Gonna get a new brake switch and try it. For the reverse lights in clueless

 

You can short the wires together on the brake light switch to test the lights. If it works you will know it's a bad switch. The switch can be checked with a ohm meter. As for reverse lights. My 68 F100 switch is on the column, C6. Try moving the selector side by side to see if it's not adj right. It too can be shorted for testing purposes.

 

That smells of a bad, or mis-adjusted NSS.

What year is your truck?
What model?
What transmission?

Sounds like it's a good thing you were digging into the lamps themselves then. Corroded sockets and bulbs is never good. If cleaning them does not help, then you might have to buy new. But try the cleaning thing first.
An eraser is a good start, but sometimes you need metal-to-metal with a brass or stainless wire brush thingy that can get down into the sockets. Careful not to dislodge the contact bands.
And while you're at the socket cleaning, clean the housings as well. Look for any separate ground wires, and any contact points between the metal housing and the body. Make sure that either the housings have good contact with bare metal, or more likely the grounding is done through the screws themselves. So make sure the screws and holes are rust free.

And since we're on the subject of cleaning electrical stuff, pull all of your glass fuses and clean them up good. Same for the contacts with your wire brush. Then re-insert the fuses.
There might even be a separate fuse for the backup lamps? I can't remember, and if yours is pre-'76 it has the small 5-fuse panel instead of the slightly larger 10-fuse version that came out in either late '75 or for the '76 model year.

​​​​​​​Try what blue68 said before buying any more parts. TEST, TEST, and TEST again!
You should have a volt/ohm meter handy at all times if you're going to work on old vehicles. Even a cheap Harbor Freight jobby will get the job done nicely. But they are a very valuable tool to have on hand. Unfortunately too often!

Test the switch first. And you can test the wiring itself like described earlier, by jumping the connections.
The brake light switch has one wire that is always hot, so the key does not need to be ON. Use a small bit of wire or a paper clip and connect one wire to the other. If the lights come on, it's the switch.
If they don't, then you need to test for power anyway. And then you need to test everything else upstream.

 

Hell just put multimeter leads on the switch prongs and bench test for continuity. The circuit should be open when the switch is pressed in (brake pedal up) because its a normally closed switch. That's how I diagnosed mine.

 

Thanks guys still trying