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rear harness has been cut. 4 wires I'm assuming going to brake/reverse/tag lights:
Green, Yellow, Black/red, and Brown

Green and Yellow to go right and left turn. Black/red to reverse and brown is the main power?
am I interpreting the wiring diagram correctly in that there's only one ground for both sides?

My brake lights have 3 wires, Green/yellow, black/red and brown.

I tried wiring the lights directly to an extra battery, but assume that all wires needed to be connected for anything to work? I thought that I could connect the black wire from the lights to the neg terminal on the battery with the pos going to one of the other wires but nothing seems to light up. even tried grounding the battery to the frame. I'll likely wire everything up as in the diagram and see if that works. Side bed marker lights only have 1 wire, as are the tag lights. I assume they ground to the frame. I'll need to dig around to see if there's another wire in the loom for the side marker lights or do I tap into the wire for the running lights.
The other green wire connected to the white wire is for the fuel sender. it's the only wire that a PO saved from the rear harness.

 

Green is right brake/signal light.
Yellow with black is left brake/signal light.
Brown is tail lights.
Black with red is back up lights.
Fuel sender wires do not pass the front of the gas tank where leaves the harness.
Tag lights are tied in to brown at very rear along with rear side markers.
Black wires from the light sockets go to ground where they are attached to body/frame.

I understand that you have a mess. I looked at those diagrams, one of them even shows green for both left and right signal/brake lights. I also saw mention of a white wire with blue tracer, At the point you are at, I'd be using a grounded test probe to test each wire ... first with 4 way flashers on, to find my two brake/signal wires ... then with park lights on only to find the single tail light feed ... and then with truck in reverse, key on to find the back up light feed. Then I'd go to my two signal/brake wires, set a signal on for left, key on, and test both of them ... only one should flash.

My guess as best as I can see the picture:


I see a Black with Red and a Green with a touch of Yellow and a third wire in the other picture .... my best guess is tail - back up - right signal/brake in that order left to right, but it'll need testing too.

 

OK, I wired up the tail lights as I thought they ought to go. Is the brown wire hot all the time or does the car need to be on start/run? Not getting any tail lights when brake pedal is depressed when the ignition is off or in the on position. Next thing to do is check the brown wire with a multi meter tool to see if it’s getting any power. Will also look into the brake switch. Previous owner did modify the original style side with a flair side bed. The diagram shows that the brake lights are internally grounded to the chassis. Wondering if that is still the case with the conversion.

 

You people and your lifts and nice concrete stained floors......I am straight up jealous, nice work area. Does that truck have "limit" chains on the rear axle? You need to probably clean out the axel vent tube tip and then put a rubber line on it.
All I have saved over the years.
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??

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.

 

yes, I'll need to clean out the axle vent tube. is it normal to have the brake lines running through that block where the vent tube is coming out? and yes, I have "limiting" chains. what's the purpose of these? this garage is a bit of my man-cave. I had it built to build a factory five cobra kit. I got this truck hence the lift so my wife would stop complaining about the truck being parked in the driveway. cobra is being parked underneath.

Thanks for the diagrams. I found these on another post that I believe you posted. I currently have 4 wires coming to the rear; brown, black/red, green, and yellow/green. As I see it, the brown is the power to the side markers, tag lights and rear/brakes, the yellow/green is for the LS blinker, the green is for the RS blinker and the black/red is for reverse. I have 3 wires coming from the tail lights; brown, black/red and green/yellow.
As I'm reading it, the brown from the rear wires go to the brown on the lights, the yellow/green and green to the green/yellow on the respective L and R lights, and the black/red goes to the black/red on each light. I also have the tag lights daisy chained to the brown wires from either tail light. From the diagram it looks as if the ground is inside the taillight, between the brake/running lights and back up light, correct?

I have everything wired as shown and not able to get anything to light up.
I assume that the blinkers should work with the car off. I tried getting brake lights to work with ignition off and on. I assume it should work w/ ignition on at the very least. I tried pulling the headlight **** to see if this was needed to get the running lights on, still nothing.
Front markers are not working for turn or hazard, but I assume that I need both front and rears wired up to have a complete circuit, right?

I'll need to get the mulitmeter out to see if the brown wire is even getting any power both with the headlights turned on and with the brake pedal depressed.

 

Yes that is the OEM way to mount the brake line splitter (2 into 1) block. Limit straps or chains are normally use to stop the suspension travel from exceeding its designed limit and or it's shocks. Was the truck a race/Baja pre-runner/tough truck competition rig?

Nothing but the brake lights, emergency flashers, and head/tail/park/side marker will work WITH OUT the ignition switch on. Turning signals will NOT work without key on. A lot of the wiring goes thru the t/s switch. Also remember you have a brake light switch on the side of the brake pedal bar.

Also remember the reverse lights lights are controlled thru the switch on the side of the trans (if a late 77,78, 79 and an auto trans.)

 

Ok I throw away all them factory pictures from the books and get your self a test light that uses an old light bulb and not a LED bulb.
A roll of masking tape and a pen to start to fix this.

Turn on the park lights, key dose not need to be on. With the test tight hooked to a good ground on the frame test each of the wires for power.
From what was posted the brown wire (but if is a different color so what) should have power and light up the test light. Using the pen mark the tape running light and rip it off and wrap it around that wire with power.

Turn off park light and turn on the left turn signal, ket need to be on for this may work in acc.
Using test light check the other wires for power, it should blink so make sure you leave it on the wire long enough to make sure it dose or dose not have power.
Pen and mark tape L/turn rip and put on that wire.

Flip to the right turn and check for power, it should blink so make sure you leave it on the wire long enough to make sure it dose or dose not have power.
Pen and mark tape R/turn rip and put on that wire.

Turn signals off and put in reverse and check any wires left over for power.
Pen mark tape B/U and wrap it on that wire.

You should have all wires tested and marked what they do.
Now you said you tried to test the lights but they did not work as they should?
My guess is they do not have a good ground. Pull the lights and clean where they bolt in to make sure you get a good ground.
Heck they way you have then temp wires, they are temp right? wired if the ground is good at each light they should work.

Now lets go back some on the grounds.
You have a cable from battery to motor right?
Do you have a cable from motor to frame? If not how is the frame grounded?
Got a ground from motor to cab / firewall? If not how is the cab grounded?
You may even want to run a ground from the bed to the grounded frame so the bed is grounded.
YOU CAN NEVER HAVE ENOUGH GROUNDS!

I had to make a new tail light harness for my 81 flare side from a style side harness.
When I first had it wired up for testing I had no lights? I was WTF then stepped back to look what I had.
That is when I seen I did not have a ground for the harness I was testing. Hooked up a test ground and all worked!
Style side harness

What I ended up with for a flare side harness

Plate harness


So you see you need to have good grounds!
Dave ----

 

Dave awesome step by step of old school wiring troubleshooting, thanks for the walk thru. I am about to start to wire up my flat bed and all I have is 4 wires hanging out a harness like the OP.

 

Thanks

My way who cares what colors the wires are.
You test each one and mark it what it dose so with just looking at the tape marker you know what it dose.
Also doing it this way you will know if you have power on each wire. If no power you need to work your way back on the harness to find out why and fix it.
Using old school bulb test over the new LED type I have heard the LEDs give a faults readings as it does not take a lot of power to make them light up.
Also using a light over a meter you can see right away if you have power. Meter you have to look at the display and maybe you will see it if the sun is not shining on it.
Also you can place the light such a way that you can test from afar like brake lights when pushing on the pedal and looking back under the truck.

I would say 99% of light issues are groundsand I am pretty sure why the OP is not getting the lights to work with the test wiring he has.
That is if the wires have power as I dont think it has been posted he dose?

Wiring for the most part dose not bother me as I have wired up a lot of plugs with brakes & power for trailers, as seen on my truck.
As long as the magic smoke is not let out all should work. LOL
Dave ----

 

Brown wire if tail, will only get power if parking lights or head lights are turned "ON". It should not get power "all the time". Brake pedal has nothing to do with tail lights.

Would have been absolutely no reason to unground any of the lights for the bed conversion, but who knows what a previous owner was thinking.

 

Man, I seem to quote this guy alot. The colors below are right. Blk/red goes to reverse lights. As stated, that Black/Red wire comes out of the side of the transmission on one side and goes to switched power on the other. Green is right turn. Black/Yellow is left turn. Brown is tailights/license plate lights/side marker lights. These are basically the four wires coming back. Two wires run to each turn signal/tail light. Brown for taillights, one for turn signal/hazards. Third wire is black for ground. ALL LIGHTS MUST GROUND TO THE TRUCK AT THE LIGHT. Reverse lights have Black/Red and ground. Side markers have brown and black ground. All black grounds must ground to the truck. There is no main ground that comes from the front. Additionally to answer your question, anything going through the turn signal switch, the reverse lights, and I think the brake lights need to have power on to work. Hazards should work without power. As should taillights, but the light switch will need to be turned on.

I hope this helps.

 

no idea what this truck did in its previous life. one thing for sure is that it's spent a lot of time in the mud based on the amount of caked on dirt that I'm scraping off the underbelly. I'll need to trace the reverse wire back in the harness to make sure it is indeed going to the trans switch.

yes, battery is grounded to the engine/frame. I'll take a closer look at the ground coming directly from the lights and clean off any contacts. good idea with the indicator test light. It'll allow me to do some investigating on my own without another person in the cab flipping switches or pushing on brakes. To be clear, the rear lights, side markers and the tag lights all ground directly to the frame of the car and there's no additional wire that is used, correct? The tag and marker lights only have one wire coming out of the housing that I suspect is for power. The rear lights have 3 wires that I presume are for tail light power, reverse and blinker.

I guess I shouldn't have said "hot" all the time, but rather was questioning if the brake lights would work if the headlight switch was off or if the ignition was in the off position.

Thanks for all the replies and ideas. I have a pretty good idea for my next moves.

 

I deal mostly in the 80 - 86 truck area being I have a 81 Flare Side.
With in the 80's trucks they did the grounds a little different. Early trucks grounded the bed to the frame but later they ran a ground wire from of all places under the dash to the rear lights as I guess they found grounds went bad over time when to frame?

Being mine is early I have no ground wire in the harness and because I should have a wood floor I have to make sure the frame is grounded good and the lights to the frame. I say "should have wood" as I used a style side metal ribbed floor in place of the wood but i still make sure the grounds are good.

The style side tail light harness I used to make my flare side harness had ground wires from each light socket that screwed to the bed behind the light housing on both sides. Again if the bed was not grounded good to the frame no lights.
I think your problem is the light housings are not grounded to the bed body and / or bed body to frame.
Why I said run a wire, 10 gauge would be more than enough, from frame to the bed body somewhere back there out of the way.
Dave ----

 

YES, brake lights and 4-way flashers will work without a key in the I-S and use the hottest filament in the bulb.
Of the rear lighting, only the back up and turn signals need key in I-S and in "ON".

 

How many volts should I be seeing in the rear light wiring with the headlights turned on?
I checked all 4 wires with a multimeter tool. The brown wire has 1.2v with headlights on. Not sure if this is normal or not.
I'll need to check brakes when I have a helper.