No brake lights! Very frustrating.

As soon as I get to some better internet I will try to show which wire I think I found.

Good on YOU!

Can you show us where that wire is, on one of the diagrams?

Remember the E-Series Cutaway wiring may be different from the E-Series Stripped Chassis, which is what you posted.

Okay - here's what we found.

I FINALLY found a wiring diagram that told me what the wire color is from the tail-light harness to the firewall connector. It is heavy-gauge wire, Light Green/Orange in color. The wire from the brake fuse circuit, 511 / fuse #39 is a thin-gauge light green wire.

I had originally thought the tail-light wire ran down the footwell and then down the rail to the harness connectors over the axle - because so many fuse-panel wires are routed this way. My inability to identify that wire really made this job difficult, if not utterly impossible. Well, MANY fuse-panel wires run down the footwell, MANY do not. I know that now.

It turns out the wire runs all the way along the frame from the harness over the axle, moving forward past almost to the firewall where it terminates in a giant harness connector that is actually bolted together!! Then, the whole shebang continues up the engine firewall behind the coolant reservoir.

I visually traced the heavy wire all the way from the chassis connector, moving forward. It was very, very well-wrapped and loomed pretty much the whole way. Once the bundle gets near the engine, the wrapping becomes even more significant - protecting the wires from engine and exhaust heat.

I couldn't assume that the run along the frame was good but my hunch was that it was okay simply because I didn't see any place where potential damage could happen.

That left the bundle from the frame connector to the firewall.

I have no way of knowing whether or not this bundle had ever been wrapped but I can say that this was, in it's current state, largely unwrapped. It seems like a pretty important bundle of wires in a vulnerable place to be left uncovered like that.

I moved the coolant reservoir out of the way to give me a better look at the exposed mass of wires (when did cars get so **** complicated???). The bundle was dirty but tight. Except for two wires which seem to have been torn, as if something had snagged them. The wires were sticking out of the bundle awkwardly.

One is yellow and blue. One of them is light green. LIGHT GREEN.

I put a test light on the upper stump of wire and shorted the brake switch.

Bingo. It lit.

At this point I couldn't be totally sure that the wire was accidentally cut or intentionally cut (for some reason) so I connected the broken wires together with a 7.5 amp fused connector I made from some wire bits. Just to be safe. Then I jumped the brake light. I heard the relay close.

Brake lights. BRAKE LIGHTS. !!!!BRAKE LIGHTS!!!

At this point I can only assume that somehow I've NEVER EVER had brake lights. Maybe.

My wife followed me in traffic a few months ago and she said she could "barely" see my brake lights. Maybe she was just seeing things. Now they're super-bright.

I can't say for sure what my situation was before I repaired the broken wire since I have never checked by brake lights before. I can't say for sure that the wire I repaired was, previously, the sole provider of current to my brake lights. I have no way of knowing. The diagram shows several wires coming off F39/circuit 511 and I did find three of those wires when it was all said and done.

In the diagram I posted earlier you can see what is basically a ground coming right off #39. It is throttled by a 180-ohm 6.5-watt resistor. I think this might be here to keep the circuit active even if all bulbs burn out (or are removed) so that some of the PCM/Brake functions will still work. The brake signal might change the engine functions - it most likely tells the transmission to downshift when you are in tow/haul mode.

I'm only guessing.

The main thing I've learned from this fiasco is that I really, really need access to better documentation. I also need to educate myself a LOT more about reading circuits. The good thing is I still value persistence. I spent three whole days on this and I even had the help of some fellow campers and even my camp-host who has a small fix-it service here in Lusk, Wyoming.

And of course I've gotten some very excellent help here on this forum (and others).

Anywhoozle, I can't be sure I've totally, utterly fixed this. Mostly because I am **** surprised that it was something as simple, prosaic and elemental as a broke wire. A. Broken. Wire.

Thanks to everyone on this thread and everyone in Lusk, WY.

(stay tuned. I hope this is my fix. maybe not. old wiring is fickle)

beemerphile1 wrote:
Have you tried WD40 on the hazard switch as I suggested? It is a known problem with Fords. You push the hazard button to use the flashers, push again to turn them off but the button sticks and the brake lights don't work.

The entire multifunction switch has been replaced. Also, I get proper voltage at fuse 39 when the brake pedal is applied. I found the grounded resistor shown on the schematic, which is a start. Right now I'm just trying to physically locate the wire that runs to the brakes.

Good suggestion about the switch, though . A stuck switch would definitely interrupt the brakes!

Have you tried WD40 on the hazard switch as I suggested? It is a known problem with Fords. You push the hazard button to use the flashers, push again to turn them off but the button sticks and the brake lights don't work.

Here's where we are. No brake lights, still. Turn signal, yes, hazards, yes, running lights, yes.

I'm getting 12 volts at the circuit with the resistors. I can't find the other wires shown on the diagram.

Are they way up under the dash?

Is your trailer plug working?

Doug

sch911 wrote:

Chris Bryant wrote:
IIRC, it goes through the turn signal switch.

X 2 and it's a fairly common failure mode too.

If you have amber turn signal lenses in the rear, then the stop light wiring does not go through the turn signal switch.

Richard

Does the hazard switch sit on top of the column in a shallow well? Fill that well with WD40 and work the switch up and down.

I'll try to find you a wiring diagram for the E450 chassis. Good luck if the problem's in the RV portion.

Stop'n'Think about it... Ford provides "trailer" wiring. It's right there and probably easier to tie into, then continue on and do the 7-pin or 4-pin trailer tow pigtail.