Brake lights electrical problem.

Bulb in dash is good.
If I switch the bulb to another socket it works.

The battery is grounded to the engine block and there is a ground strap to the chassis. Running another ground from the battery to the chassis with a good connection did not change anything.

The front light gets power, but only to the running light circuit, the turn signal circuit is not getting power.

The turn signal switch is new. When putting a test light to the connection on the turn signal switch the test light will flash like a turn signal should so that has been eliminated as the issue.

Both rear lamps have running lights and turn signals. But the brake light only illuminates on the left side and only with the left turn signal on. This will also work with the key in the off position and the turn signal switch not getting power.

I can see the entire wiring harness and there is no rodent damage. Some of the harness is wrapped, but I do not want to start pulling it completely apart without knowing what I am doing first.

I have wiring harness diagrams, they do not help tell me what circuit is creating this issue. I believe this situation requires someone with excellent knowledge of electricity and how circuits work.

Something in the circuit is causing this issue and I am looking for help for the things I have not done yet, so here is my list:

Replaced: Flasher relay, turn signal switch 30 feet of bad wiring in the bed area, all the bulbs, 3 sockets, 4 lamp assemblies, head light switch, all fuses, battery cables, added a ground strap from the engine to the chassis.

My original problem was that I had no running lights, no turn signals, no dash lights, only head lamps and left rear brake light with turn signal engaged.

Doing the above repair/repalcements corrected everything except brake light and turn signal issue as stated above.

I can send you the wiring diagram I have to study. It appears to me that the only place that the brake light and turn wires come together are at the connection to the turn signal switch. Maybe there is a short circuit that is feeding back in that area, but I do not know how to test this. Are you able to step by step help me test these circuits?

I have a test light and a volt meter.

I have the correct bulbs.

I tested the switch at the connections and it works fine for the turn signals.

Not sure where to hook to to test the brake lights.

The switch was NOS and they are not available any more, so if it turns out to be the problem I have to figure a work around or repair it. However the problem with the brake and turn lamp occurred with the old switch as well, so I doubt the problem is there.

The power is not reaching the connection at the front light. The problem lies somewhere else and the fact that the cluster indicator does not flash as well is part of the problem. I get the relay to activate and the rear lamp to flash, but that's it.

The ip socket checks out and is good.

What is really confusing to me is that I can swap the connections coming off of the t/s switch ( the ones supplying power to the lights) and either way I hook them up the t/s work the same. I am beginning to think I have the wrong t/s switch, but that does not make sense because it looks identical to the old one and gives me the same problems.. Of course maybe the old one was wrong also.

From your email: "Ok you don't or shouldn't need the ignition on for the brake light test. Take your test light and probe the red/blk wire gong to the t/s switch for power. If it has that then probe the green and yellow wires for power they both should have that with brake pedal applied. If no power then it's a t/s switch problem of some kind. Then probe the green/white wire that is for your dash light and front parking light. If power there then pull the cluster and probe by bulb to see if it is getting power if it does then it may be a bad bulb connection which the interior guts can be replaced without the whole base. Power will be needed for those two. Then probe green white wire near front turn signal see if gets power. If it does then it may be a bad socket which are also available at auto parts. You just need the guts. The bulbs should either be a 1034 or 1157 with two filaments for front and back t/s lights. The corresponding wires in rear will be yellow and green for the sides the brown wire in back is for taillights, etc. Let me know what you find. Make sure the bulbs are the ones I've said in front and back because this can cause problems as well if the wrong ones installed. "

I tested the red wire to the brake light switch and it has constant power.
The red/back runs from the other side of the brake light switch to the t/s for power.
With the brake pedal depressed the red/black has power going into the t/s switch.
No power comes out of the t/s from the green or yellow wire.
When I engage the left t/s the yellow wire has power, but nothing still from the green in any position.
I put direct power to the yellow and green wire in the harness and I get illumination on both rear brake lights.
I put a jumper from the red/black wire to the yellow and green wires and I get illumination on both rear brake lights.
So it appears that the $150.00 NOS switch I purchased from eBay last November is crap?
I would like to take a look inside of the switch and the cam assembly is a still available serviceable part, but I cannot figure out how to remove the retainer from the pin holding it on.
This does not seem to be too complicated a device and I think my only option is to disassemble and repair it. Your thoughts?

I got the can off. Everything looks fine in there. I am suspecting that the wires are in the wrong place and I need to find a schematic showing what color wire is supposed to go where in the switch.

I solved the problem. Thank you for leading me to the t/s switch.

There were two issues that came from it being assembled wrong.

1. The small actuators in the switch were installed upside down and backwards, so they were making the wrong connections when the switch was activated and were feeding power to the wrong circuits.

2. Two of the wires were switched and going to the wrong plugs.

I had to rebuild the switch so the actuators were installed correctly, and cut the plugs off and go through each circuit one by one to determine proper placement to where they were supposed to go in the trucks harness (since the wire colors were useless at this point due to the manufacturing defect.).

Once I did that I was able to troubleshoot and correct the placement of the two reversed wires, reconnect the plugs in the proper order and heat shrink the junctions. Now everything works the way it should have when it was originally built.

The irony to all of this is that the likely reason this part was still available was because it had been returned as defective and the dealer just put it back in inventory.

The fact that this part has been discontinued left me with no choice but to correct the manufacturing errors.

It was a genuine Ford part. However I know they use outside vendors. This particular part is not available after market. I bought it out of new old stock from a ford Dealer.