Hello.
I couldn't reset password due to no longer having the same email, so new account. Long pos. I apologize but including as much info as possible.

I have a 1977 F150 flareside (bed is from 80's). Manual transmission, no tilt or cruise or anything. Aftermarket steering wheel and horn doesn't work (never has since I've owned).

My issue is I lost the lights to the rear. No tail Lights or brake lights. Turn signals come on, but VERY dim. 1 reverse light worked. All lights worked when I purchased truck and did until recently

I started checking the basics. I ran The power probe to the lights to verify bulbs are good. Checked grounds and everything seems to be good. I started looking at wiring...a mess. P.O. spliced a trailer adapter in. As I'm tracing the wires back, I found one wire broken, 1 smashed under a bolt (IDed as backup light. Explains why only 1 worked), and a frayed wire in the frame harness. I took rear harness at bumper off and brought in to test. Ran new wires and connections. Used power probe at connector to test connections and lights were dim but all worked. I decided to rewire everything and splice in the plug. Still getting dim lights so I bypassed the plug and ran connectors. All lights corrected brightness. Disconnected harness from front fender and ran new wires all the way back and spliced into factory connector at front.

Tested lights and i get a turn signal. Hazards both work. No backup, no tail lights, no stop. Stop light switch seems to work fine. 12v on one side and when pedal depressed, 12v on other side. With headlights on, I have nothing. Front headlights and marker lights all work correctly.

where do i go next? I hooked the power probe up and looked at connectors on TSS. Powering a few of the connections with this gave some lights (wife confirmed as I couldn't see them). Headlight switch is brand new. Old headlight switch doesn't change anything. My assumption is bad TSS but I can't for the life of me get the connector apart to get it out of column and inspect it. Any tips on this? Any help is hugely appreciated.

 

"With headlights on, I have nothing"
- Bad Grounds.
When the headlights are off, the other lights are back feeding- using that circuit as the missing ground.
When the headlights are turned on, that ground is eliminated, causing the other lights to go out.

"Hazards both work"
"no tail lights, no stop. Stop light switch seems to work fine."
- Turn signal switch or tss wiring.

"I found one wire broken, 1 smashed under a bolt (ID as backup light. Explains why only 1 worked)
"No backup"...
- Conflicting statements. One backup light worked, then you fixed the smashed wire, now nothing?

 

The harness of rear wires travels rearwards from under the cab along inside the left frame rail. In that harness is light wires and a wire from the gas sender. Just above the rear axle, in front of the tank, the gas sender wire exits the harness. The harness with all the light wires goes through a hole with plastic grommet, and travels on back between the gas tank and left frame rail. It comes out through another hole in front of the bumper.

• Yellow/Black is the left turn signal / brake lamp hot
• Green is the right turn signal / brake lamp hot
• Brown is the tail lamps, tag lights, side marker lamps hot
• Black / Red is the backup lights hot
• Black is chassis ground, I don't believe that its in the harness itself. Left and right side lamps are grounded to the chassis on their own sides of the truck. A good ground on the left rear does not ensure a good ground on the right side. I don't recall there being a long black ground from side to side, the tag lights ground in the bumper metal.

If you find other colors, well .... someone did swap beds. Check the condition of the harness. Test the wires for function. Brake and turn signals are controlled in part in the turn signal switch, it interrupts a brake lamp when a turn signal is requested. Front and rear signal lamps are tied in to the 4 way flasher switch.

Once I had rodent chew damage behind the tailgate, and last year found damage from rodents between the gas tank and left frame rail.

 

Ok thank you for this. Soon as the storms pass, I'll go clean up a good place on frame and run new grounds.

As for the reverse, yeah it's weird i fixed the smashed wire and nothing. Maybe this goes back to the ground. I'll check it once I fix the ground.

The TSS was my next to do as soon as i can get the connector loose. That sucker is latched on like 2 5 gallon buckets lol.

Thanks

 

So I did go through and replace all the wires front to back from the connector under the hood.
I'm going to run new ground wires to the lights to see if that changes anything. The light housing is "supposed" to be grounded through the bed. Note the " " haha.

I verified with the power probe that the wire connections are good. I did find a squirrel nest but luckily no damage. I'll post my findings once the storms pass and i can get back out to it.

 

To enhance the ground between the bed and the frame, you might just run a simple jumper wire between the two.
They usually have a good connection through all the bolts, but after this many years, age might have taken its toll. Between rust, possibly paint and undercoating, and any number of other things, the bond between the bed and the frame might’ve deteriorated.
And to enhance that even further, make sure that your battery has the two grounds and probably an extra one between the engine and the frame. Or the body and the frame. Doesn’t matter.
The main cable still goes to the block, of course, but there should be a separate dedicated ground to the inner fender. Should also still be ground between the back of the intake manifold/engine and the firewall.
The bed is still a separate entity from the cab, so it doesn’t hurt to make sure that everything remains interconnected. You may or may not have the original ground straps between the body mounts and the frame, so you might check that. But either way, adding a ground jumper between the bed and the frame is not a bad practice.

A single 10 gauge wire would get the job done. Or one of those premade braided ground straps that you can buy on the HELP rack at the auto parts store does a great job.

 

Not saying grounding is you’re only issue, but at least doing all of that would eliminate it as a possible gremlin.

 

small comment, remember a poor ground at the front can affect function at the rear.

 

So I think I still have a few issues going on. No power to the headlight wire at the frame harness. At the harness that comes out of firewall, with lights on, I have over 12v. Nothing after the other connector so bad connection. Gonna try to source another connector or complete frame harness.

Tested the bulbs at the rear of truck with jumper wires. Used a different battery at rear just to ensure sockets are good. With the light housing hooked up and bolted (lights are supposed to be grounded thru the 3 bolts) and only a hot wire. No lights. When I touch the ground jumper to the metal in housing, lights. So, looks like there's definitely ground issues as well. Gonna go through and verify and redo grounds. Just started at front and gonna work my way backwards to redo all grounds. Hopefully can get the new pigtail adapter and Fox the grounds, then can hopefully have lights. Thanks for all the input. Will post back once I figure this mess out.

 

Is there a specific place on the block to find the ground to frame? I can't locate one anywhere. I cleaned up battery to block, block to firewall. That's all I can find though. I ran a ground directly from battery to tail light housing and got some pretty bright lights, so can confirm part of the issue is ground. Doesn't explain lack of power to tail lights through the connector though

 

This guy was on the money!! I ran a ground from starter to frame since I couldn't find one any where else. Then I tapped a bolt and ran a direct ground from light housing to frame and we are back in business. The reverse lights not working after I fixed was my own blunder. I somehow didn't crimp the wire correctly and it wasn't connected lol.

Thanks a million. Now to tidy up the wiring and secure it.

 

Glad you got it figured out !!!