Electrical Help Needed - Strange Problem
 

Strange electrical issue involving my LH rear turn/brake light on my 1998 Ford E350 cutaway chassis motorhome. Even looking at my wiring diagram I can't tell how it could be happening. It is straight forward*"old school" system, no "magic boxes". Any help on understanding this will be appreciated!

Below is a condition and result breakdown to simplify the problem:

*1) Brake pedal depressed - Both rear brake lights 'on'

*2) Brake pedal depressed & LH Turn selected - LH rear nothing; RH rear brake 'on'* (steady as should be)

*3) Brake pedal depressed & RH turn selected - LH rear nothing; RH rear turn flashing

Note: The front signals and I/P indicators always work as should*

*4) Brake pedal released - LH turn selected - LH rear nothing; Front and I/P indicator flash

*5) Brake released - RH turn selected - Rear, Front, and Indicator all flash

*6) 4way selected - no lights at all

*Now the really strange part: I removed the trailer LH turn (as per owner manual) #6 fuse (which is good) <#26 on the wiring dig> and reinstalled it. All turn lights work as should and the 4way*operation is normal. :confused:
If I step on the brake pedal all goes back to condition 1-6!!! Reset fuse and again all is norm until the brake is applied.*:mad:

I hope someone answers your question, my neighbor has a 96 E 350 motorhome chassis that does the same thing. I spent about 3 hours working on it last fall, and all I got determined was the wiring from the driver area to the rear of the vehicle was okay. without a schematic I wasn't going to start chasing wiring up under the dash.

I have a suspicion it may be the turn signal switch, but I've never had time to get back to it.

It has another thing that I never chased down either. Plugging my scanner into the OBD II system shows nothing, no readings whatsoever. Of course it's a neighbor, so he expects me to do it for free, my time is too valuable to waste a few days chasing electrical problems on some 25 YO motorhome.

Last I knew it wasn't starting, so maybe he'll give up on it, his health is declining due to cancer, and he told me he's not well enough to go camping any longer.

I like the guy, but he has zero mechanical aptitude, and buys old cars that have problems that aren't easy fixes. The place looks like a used car lot, and maybe 2 of the 15 vehicles he has, run, and are roadworthy. The rest just sit in the yard. I think when I bought my house, and he found out I was a retired mechanic, he figured I was going to get all his junk running, I have plenty of work to do on my own old junk to keep it on the road......;)

I would replace the turn signal flasher unit and the hazard flasher unit.
I would think one or both are bad?

Make sure you get the correct ones for each unit. (they are usually different)

While replacing them check for any corrosion or anything out of the ordinary.

:confused:

I would suspect the turn signal switch and/or hazard switch as well. If you think about it (regarding vehicles with dual purpose rear lights meaning the same light acts as brake and signal) with no signals on, brake lights come on steady burn when the pedal is pressed. Then with the brake still pressed turn a left signal on and the signal has to “interrupt” the solid brake light feed to provide a now flashing feed to the rear bulb. This is all accomplished by the turn signal switch. Hazards work in the opposite fashion so that when the hazards are on but brake is not pressed the lamps will flash. Press the brake and the lights (both rear and both front) are “overidden” and now solid burn until the brake pedal is released. This works in a different way that I’m honestly not 100% clear on but I think the signal switch is where I’d consider starting.

Your fuse removal changing things, I’ll have to ponder a bit more if nobody else beats me to a solution.

Didn't see/read results if you left that #26 fuse removed.

Clay

By seeing your quote it caused me to google "unit" and I came up with something that may be there that is not on my wiring diagram. But this, I could see as the problem if it is there!

video: https://www.youtube.com/watch?v=g6ZnneC7lCM

Image: https://static.cargurus.com/images/s...1600x1200.jpeg

Thank you for all the replies. I just haven't had time to check it out again and don't know when I will be able to. However whenever I do I will post what I found and hopefully that can help you out Sirrotica as well.

Start basic, find all the grounds and clean them and make sure they are tight.

X2 with SSR,strange things usually = poor grounds.

Grounds are not the problem on my neighbors motorhome, that's what I was expecting to find when I tore into it. All the wiring, and grounds in my example have already been checked, the problem is supply voltage in the cabin area, and just a guess on my part would be the turn signal switch. Mine has one side that works (left) and the (right) side turn signal, and brake light have no power supplied all the way to where the harness goes through the floor. Tail lights work on both sides.

After 3 hours it was getting dark, and it won't fit in my garage, so I threw in the towel. I'm hoping he sells it, or junks it, and I won't have to mess with it further, but I'd still like to know what the problem is. When I don't repair something, I still wonder what the problem is, I should probably just forget it.

It was a gratis job so after 3 hours I figured I made an honest attempt to find the problem. I didn't want to invest days into it, especially after I took a peek under the dash and saw a rats nest of cobbled up wiring.

Finally got a moment to look into this problem some more on Friday.
I plugged a tester into the trailer conn that beeps when it has a signal and grabbed a test light.

- with the ignition 'on' there is constant power on the RH Turn Trailer fuse , no power on the LH fuse.

- select RH turn and everything works as should and power on fuse is still steady

- select LH turn and again, I get front lamp flashing but not rear and no "beep" from tester, no power on LH fuse

- I left the turn lever in the LH postion and continued with my unrelated task of empting the fuel tank using the generator fuel pump, and 20-30sec later I hear the tester beeping. Sure enough the rear turn is flashing and the i/p indcator is. I check the fuse and the power on/off in sync with the front lamp!

- I step on brake, no problem (unlike before). I select RH turn and press brake and all works as normal (unlike before)

I continue 'playing' the the LT/RT signaling and brake applications and the system just continues to function normal.

So then I shutdown the van and wait a couple hours and try again, first the LH turn. At first it it does not work, then after a short delay maybe 5 sec it starts working again.

Yesterday (Sunday) I took it out for a drive around town and it worked fine and with no delay in LH signaling operation.

So it did a "self fix" as of now, (or the fuel level has to be below 1/2 tank LOL).

However what is "Normal" by design, constant power on the RH fuse with ignition on or 'flashing' with the turn selected as on the LH???

Crazy!

Off-hand, I'd say it's a ground situation?
With the fuel sender being part of the 'solution' it is a source of (more) ground?


:confused:

I was just joking about the fuel sender :D and I understand that bad grounds can cause all kinds of crazy things. I had a '68 Firebird and those tail lights were forever causing all kinds of weird issues because it's poor grounding through the mounting clip studs. Solved that with dedicated ground wires. :clap2:

:focus:

Anyway the grounds on these motorhome tail lights check good and are hard wired since they are attached to fiberglas.

.

Relay inside flasher, IMHO. It WILL be back..

I imagine you are referring to this C239 Electronic Flasher that I cannot seem to find. Must be hidden real good!

Do you happen to have an idea of where it is actually located in the van? Wiring diagrams always make it look like "well right there!"
If it's the one in this video I must really need to do some more digging, cause I don't see it as easy as this shows! https://www.youtube.com/watch?v=g6ZnneC7lCM ,but then this vid is a pickup not a van.

.