Any tips to troubleshoot tail light wiring?

[belfert]

My tail lights have started to blow the fuse as soon as I turn on the lights.  Strangely enough the passenger side marker lights are out too and I thought they are on a different circuit.

I have done the obvious like inspect the wiring harness from front to back.  I also replaced the 24 volt relay used to control the 12 volt lights.  My Dina does not have a side mount electrical panel like most buses.  The electrical panel is inside the bus above the driver's head.  I was driving screws into the floor recently to anchor walls, but the wiring harness runs nowhere close to those areas.

Any tips to help troubleshoot this without making Buss rich on 10 amp fuses?  I tried the wiring diagrams and I just got confused as the lights are spread over five pages.

I talked to Bryce Gaston (Busted Knuckle) and he said that his friend Bobby has had this same issue with Dinas and he wants to or has rewired the rear lights on some of his Dinas.

[Dreamscape]

I don't know anything about Dina's but I'll give it a try.

Sounds to me like your hot wire is grounding somewhere. I would isolate the wires and do a continuity test to ground and see if you find anything.

Good Luck,

Paul

[luvrbus]

Belfert, unplug all the lights on that circut install a new fuse if it blows it is a wiring problem if not it is a light plug each one back till the fuse blows and that will be culprit, also check for water in one of the lights  10 amps sounds a little weak for lights even with a relay  good luck

[bobofthenorth]

luvr has given you good advice.  What you want to do when you are troubleshooting electrical is break it down into chunks that you can test individually so you have a limited number of variables.  Use jumpers to bypass confusing bits.  If wires disappear into some area and emerge much further away then if you can bypass that area that will tell you if it is good or not.  I find sometimes it helps to write down what I am doing as that sometimes shows a pattern that isn't otherwise immediately obvious.  And don't assume anything - I had an open circuit in my ProHeat last week that turned out to be a cold solder joint inside a glass fuse. 

[belfert]

Belfert, unplug all the lights on that circut install a new fuse if it blows it is a wiring problem if not it is a light plug each one back till the fuse blows and that will be culprit, also check for water in one of the lights  10 amps sounds a little weak for lights even with a relay  good luck

The 10 amp fuse is strictly for the tail lights and rear clearnace lights.  The brake lights and turn signals are on seperate circuits. 

The brake light fuse was upgraded in a service bulletin to 10 amp from the original 5 amp.  The fuse would blow if all the lights were actually working.  (Only two of the four brake lights worked originally.)

[boogiethecat]

Ok here's a tekkie solution that works really well BUT may not be something you can grokk...

If there's a short to ground in a circuit somewhere, and you consider your wiring in that circuit to be something like the branches of a tree, you can figure out where the short is by putting a reasonable current through the wire (a few amps) and measuring voltages along that wire with a sensitive voltmeter.  You'll need something that can measure down to 1 millivolt DC, like a 4-1/2 digit digital voltmeter...

Practically speaking, you'd do something like this:

Turn the breaker that blows OFF (or remove the fuse if that's what you have), then get an old headlight and hook it across the breaker or fuseholder.  The headlight will light up, since one side of it is hooked to the plus side of the breaker and the other side of the headlight is grounded via the unknown short on the other side of the breaker.  This puts a very constant current through the wiring between the headlight and the short, and due to ohm's law plus a finite and measurable resistance of the wiring, this will also put a measurable (although small) voltage across the wiring, between the headlight and the short.


Ok now, MAKE SURE YOUR METER IS ALWAYS GROUNDED TO THE SAME PHYSICAL PLACE (preferably at the battery, and use a long piece of wire as a "ground extension" if necessary) and preferably remove all lightbulbs and other current drawing things that are on the circuit, although this may work ok if you don't...

Now, if you use a sensitive voltmeter (like a 4-1/2 digit fluke meter, etc) and measure the voltage between ground and the "shorted" side of the headlight, you'll probably find a few hundred millivolts, due to the resistance of the wires between there and the short to ground.


Now, start measuring the voltage in other locations of your circuit.  As you get closer to the short, the voltage will go down and down until you finally find the short, it will be near zero millivolts.

If you head off on a branch of the circuit that is not shorted, the millivolt readings will stay the same no matter where you are on that branch of the "tree"; in this case try somewhere else. 

Follow the decreasing millivolts and you'll find your short.

Sound clear as mud? Kind of a tekkie solution but it works really well....

[Sammy]

Water in light housing is most common cause, as already mentioned.
Do a visual check of each light assembly first- wet, loose connections, grounding out,etc,etc.
Good luck.

[belfert]

I'll try removing the light bulbs and doing more testing this weekend when it is light out.  It is getting dark pretty early these days.