Electrical Tail Light problems Need help A.S.A.P.

[John Scott]

Having problems with my 89 Mallard.

It recently passed N.Y.S. inspection but I just discovered a really weird tail light problem.

Tail lights, brake lights, directionals all work normal when the head lights are off.

When the head lights are on, Tail lights, and directionals work right but there is only brake lights on the passenger side, nothing on the drivers side.

I have some basic electrical and trouble shooting skills, but I'm no electrician and started looking for bad connections, wiggling wires, etc. etc. No luck.

I suspected a common ground problem and spliced into the, Green ground wire and jumped directly to the frame. Viola!!!!! Brake lights worked!!!!!

But the real fix is not that simple because once you take your foot off the brake the tail light fuse blows and now you have nothing. I tried this 3 times and blew fuses each time.

Does anyone have any ideas?

Thanks, John and Barney the Beagle.

[Gary Sterner]

Hi John, A word of caution! DO Not bypass the offending fuse in any way. This could cause a fire and burn your rig to the ground. Cancel the trip until you find the problem.

 I believe you have a short somewhere relative to your brake pedal assembly or vicinity. Although the problem I had was with my '72 Chevy 3/4 Ton P U truck, yours sounds very similar. My rear brake, turn signal, and running light circuit was repeatedly blowing it's fuse, and after doing all the above to no solution, I purchased a fault finder on FEEBAY and did in fact find the offending wire. It turned out to be the interior dome light pressure switch in the drivers door jam. The connector on the back side of the switch is a round female, and the circuit wire connector is male, which became undone and just dangled inside the metal kick panel next to the floorboard. Every time it would contact the inside of the kick panel, it blew the fuse. This @%#*&!++++  drove me crazy for some time, and I actually quit driving the truck for awhile because of the no lights danger and I didn't want a ticket.

 Some things you might try before you purchase a fault finder.

 1. Check all around the brake pedal assembly in the dark, with someone else depressing the pedal. This way you might be able to see the little sparks from the shorted wire before the fuse blows.

 2. Get a copy of the wiring diagram for your rig if possible. You can trace the wires one by one, starting at the fuse box and going towards the inoperable tail lights to try and find the short.

 3.The brake light switch could be the problem. I.E. Worn out, loose on it's mounting, poor connections, etc.

 The solution is prolly quite simple, you just have to find it. I hope I've been helpful.  Let me know what you find out. Regards, Gary S.

 P.S. Get a real good supply of fuses.

[Richard W. Cobbs]

I agree with all except the p.s.  Find a way to rig up a reset-able circuit breaker.  Save it, you'll probably need it again.

[Gary Sterner]

Very good tip Richard. Are these available in different amperage's and where to buy? Thanks.

[John Scott]

Thanks for your replies, Brake switch ruled out.

Brake lights work fine when head lights are not on.

Only have brake lights on one side when headlights are on, tail lights are fine with head lights on.

Bad ground ruled out, and doesn't make sense that it would be as everything works normally and lights up with head lights off. I crawled underneath today and found two different after market trailer wiring sockets.

It looks like a major rats nest of feces under there. The wiring is not neat and haphazard at best.

I'm thinking some one in the past may have miss wired these sockets in and spliced into something wrong and cut the hot feed to the brake lights on the drivers side, on a headlight circuit.

Again, everything works fine until you drive at night. With head lights on everything is fine until you hit the brakes and only have brake lights on the passenger side.

So this problem could have gone on a long time and  if you only drive during the day it would not be obvious.

I'm working on getting up in the morning, crawling underneath and cutting all the rat nest feces, sockets out and throwing it in the dumpster cause this is p------ me off to no end.

The heat here has been in the 90's for a week with oppressive humidity. You can just stand and do nothing and the sweat will just run off you.

I already know that between the heat and humidity and dealing with this wiring insanity that I'll be plenty F------ p----- off!

It's the little things like this in life that make it special and aggravate me to no end!!!

[Gary Sterner]

I feel for you John. I once had a 1953 GMC pickup with similar wiring under the back end. About a dozen short pieces of different colored, and different sizes of house hold extension cord twisted together. Rewire is the only real solution. If you can find where the original circuit was spliced/rat f_ _ _ ed, you might be able to get it working as it should. It sounds like you've found the culprit. Good luck with this problem, and try not to let it stress you too much.

 We've been having 90 degree heat as well. I take cold showers and then put my clothes back on with out drying off. It helps to get a fan going where you're working if you can as well.

[Richard W. Cobbs]

Circuit breakers  

Because I am out of the U.S. I have to get my stuff through Ebay, but auto parts or auto sound stores should have something.  There is a wide range of sizes for auto sound systems, up to 250 volts!  Man that should let em know you're coming!  I put them inline from my battery to my 1200 watt inverter.

[John Scott]

 Yes, have a meter. Thanks so much for your offer, it is very kind.

[William Martin]

We recently had a similar "weird" problem with the lights.  Same kind of crazy things you are describing.  Figured out it was the tow vehicle (the lights were goofy on all 3 of our trailers).  We suspected a ground also and went directly from battery to wiring, but still no good.  Finally took it to an RV place that works on our type van/truck a lot.  They found it in less than 1 hour - a special "body ground" within the vehicle itself.  The strap for the ground was behind the passenger seat.  We would have looked for months and never found it or known about it.  You might check with a local RV repair shop that does a lot of wiring to see if they know of any secondary or body grounds on your tow vehicle.  Solved our problem quickly and was about $125 parts and labor.  Worth it to have the problem solved.

[Mike and Heather Brancich]

Just some food for thought, all the light functions run through the turn signal switch in the steering column, I have ran into this on many occasions, If you don't run into a bare wire, but you still show a short in the system with your multimeter, unplug the connector at the bottom of the column that leads to the turn signal switch and then check for a short with the multimeter. If you want to friend me, I will give you my phone # and you can call me, I am a retired tech of 30+ years, and am willing to help you. Also, you can purchase a short finder at Oriely's or autozone, It is a very helpful tool in my toolbox.

                                     

                                                          Good Luck    Mike