Brake Light Failure

[Norm Green]

When I was doing a light check prior to leaving last week for the Memphis rally, I had all lights on my tow vehicle, 06 Jeep, but no brake lights on the coach.  All other lights on the coach worked, turn signals, tail lights.  Unable to find an easy answer and the fact that it was raining cats and dogs and knowing I had all the lights working on the Jeep, I decided to go ahead to Memphis, from Nashville area, and try to determine the problem there.

I found a 15 amp fuse for the break lights located in the electrical bay that was blown.  I replaced it and watched the back of the coach while Cynthia stepped on the brake.  The brake lights came on for about 5 or 6 seconds and then went out.  The new fuse had blown.  I then put another new fuse in, check for voltage on both sides and confirmed good.  I then asked Cynthia to turn on the 4 way flashers while I watched from the rear of the coach.  All the appropriate lights flashed for about 5 or 6 seconds and then went out.  I checked for turn signals and had none.  I inspected the brake light fuse and it was good but I had blown the hazard warning fuse located just above the brake light fuse.  Replacing the hazard warning fuse gave me back my turn signals which work fine but I did not turn on the hazard warning button, running out of good fuses.

I am clueless with regard to what is wrong.  I don't think it is a direct short because the lights stay on for a few seconds before blowing the fuse.  Any ideas and suggestions would be greatly appreciated.

[Stan Simpson]

Norm,

When you say blown fuse, do you mean the resettable breakers in the electric bay? Perhaps our coach is different, but there are no fuses in our electrical bay.

Stan

[Norm Green]

The electrical bay accessible from the outside below the driver.  I have numerous automotive spade type fuses.

[Bill Sprague]

Norm,

I'm going to offer the guess you have a short near a bulb socket.  Maybe even a corroded socket.  Consider removing one bulb at a time and trying again.  

[Edward Buker]

Norm,

When you add the car taillight load on the rear taillight circuit of the motorhome it is a marginal situation as far as the fuse value goes. Sometimes they will accommodate the extra load and sometimes not. The fact that it takes 5 or 6 seconds to blow one means you do not have a short, you have a marginal overcurrent situation. Up the fuse size by 5 amps on the 2 circuits and if you blow one of those go looking for a problem. Also check the contacts on the connections where the car power cable plugs in for corrosion. Spray those plugs and receptacles with WD40 and push them in or out a few times to renew them.

Later Ed

[Norm Green]

Thanks Bill and Ed.  I have checked all the bulbs in the rear of the coach and all are clean with no corrosion.  I forgot to mention that the original problem I described is without the Jeep wiring connected to the coach, although I also had no brakes when I left home with the Jeep connected.  All the testing I have done today is without the toad wiring connected.

[Edward Buker]

Norm,

If you did not have the toad attached then you have to assume that you have a bad connections somewhere or a wire that is nearly shorted with some resistive coupling to ground. The most likely candidates are the rear tail lights that see a lot of water wash at the rear of the coach and the plug and wire connections on the coach that couple to the car, usually a round multi pin female or male receptacle. I would pull that apart and verify that no stray strands are touching things they should not and that the connections are clean and tight. Below the light socket contact points is a spring and a set of connections that could cause issues. I would spray those sockets with WD 40 and check them closely. If that does not yield anything then I would get hold of a DC clamp on ammeter and start to measure the current going to accessible wire locations that feed each light to see if they are even left to right etc. If you can gain access to the fuse wire you could clamp on there and wiggle sockets and remove individual bulbs and see if the current is modulated beyond what you expect. This is not an easy issue to find if it is obscure, hope the source becomes apparent. I would also see if BCS in Bend might provide the likely candidates they have come across with your issue.

I have this meter and it works quite well.

http://www.amazon.com/CEM-Dt-337-Measurement-Tester-Resolution/dp/B00ES4L9P4/ref=sr_1_4?s=industrial&ie=UTF8&qid=1410822551&sr=1-4&keywords=dc+small+jaw+current+meter

A simple analog meter wired in series at the fuse holder temporarily will work well for this measurement and does not require zeroing and errors associated with clamp on pick ups.

http://www.amazon.com/Analog-Current-Panel-Meter-Ammeter/dp/B0050GIN2Q

Later Ed

[Mike Merchant]

Norm,
Had similar problem a couple of years ago. Local eagle-eyed trailer wiring guy noticed one of the dual filament brake light bulbs had one filament broken loose on one end which then sagged down onto the second filament resulting in an unhappy electrical situation. New bulb, end of perplexing problem.
                                                                                                                                          Mike

[Norm Green]

I inspected all the bulbs once but will do it again to make sure I haven't missed anything.  I appreciate the idea.

[Norm Green]

I am still trying to locate the cause of my light outage.  I have inspected all the wire that is reasonably accessible and have found nothing wrong.  All light bulbs are good.  I have inspected under the dash and inside the drivers side console and have found nothing irregular.  Can a relay cause the fuse to continually blow when brake lights are applied?  Any other suggestions appreciated.

[Norm Green]

I remembered one other thing that was odd.  While driving home from the Memphis rally, with the engine brake light off, when I took my foot off of the accelerator, the transmission responded as if the engine brake was on.  I checked all the wire connections of the engine brake switch and they seem to be in proper location.  Just another thing to add to my frustration.

[Edward Buker]

Norm,

That can be a perfectly normal condition if the ECU is programmed to enable that braking option and you have left the jake brake switch in the on position while driving.

Later Ed

[Norm Green]

Ed, I agree, however, the switch was in the off position.  With the switch off, the engine break seemed to function as if it were on.  I am struggling with a couple of consciences.  Prior to leaving on this latest outing, I replaced the instrument cover next to the drivers left armrest.  That required the removal of all the switches which required removing all the associated wires.  I labeled the wires, took pictures prior to starting and made a diagram to ensure that I put them back in place.  Prior to this trip to Memphis, the last time we had the coach out was the end of May.  At that time I had brake lights and I don't recall that the engine brake functioned unusually.  

The current situation may or may not be related.  Maybe I put the wires on the engine brake wrong but I have checked carefully and I don't think so, but then again I don't have any other logical explanation as to why I have these two issues.  I spent all day yesterday trying to find an obvious cause, looking at all the wiring in the armrest consul and elsewhere in the coach.  Not sure what to do from here.

[Edward Buker]

Norm.

if you now put the switch in the on position does it act as if the engine brake function is off? That test would tell you if the switch functions seem to be reversed or if you are in the on position no matter which way the switch is thrown.

Later Ed

[Norm Green]

No, it appears to function in the on position regardless of the switch position.  I have just spent another 6 or so hours trying to run the problem down.  At this point I am ready to find a local mobile RV service provider to help me out.