Headlight problem

[prpickett]

I've had a recurring problem, blowing the fuse for the running/ side marker lights. I finally got down to troubleshooting and thought that I had fixed the problem by replacing the headlight switch. Turns out, that was a symptom, not the problem. Looking into it closer, I have determined that the fuse blows when I rotate the headlight switch towards turning on the courtesy lights. The fuse blows before I complete the connection for the courtesy lights so the problem is in something that gets power from the dash lights. Everything seems to work fine until the switch is turned to just before the courtesy lights turn on, basically the max brightness for dash lights. I tracing through wires now, but was wondering if anyone else has noticed something like this or what else gets its power through this circuit (radio lights?, CB lights?, etc....). Finally, once this gets fixed I can move on to finding my roof leak, that'll be a new thread. Thanks for reading.

[Romeo]

The first thing I would suspect is the dimmer control. I cant think of a good way to check it, however. Those switches are commonly available at auto parts stores. Whatever you do DONT go to Newmar, or any other RV parts supply, for one. They will charge you a fortune. I didnt replace mind when I thought I needed one, but did ther research to find that they are cheaper through auto parts stores.

I was trying to get my dash lights brighter, but found that it was the Demux controller rather than the dimmer switch, and that was about $300... decided to live with dim dash lights.

[prpickett]

The dimmer switch is integrated in my headlight switch (old style, same as late 70's GMs). The old switch was bad (no resistance change with rotating the knob) but the new one shows a resistance change (from 7 to 4 ohms) so I am assuming it is good.

[prpickett]

Just blew the new switch. Turns out the wire leading to the dash lights is grounded. Now I have to start labelling wires so I can disconnect the dash to trace out the ground. Looks like I have about 2 miles worth of wire nested under the dash to sort through.

[Dirtbuster]

It might be a good time to buy a wire tracer, I believe they are fairly cheap at Harbor Freight!

["007"]

You may want to look for wires chewed in the wiring harness for starters or harness resting on any metal framing on fire wall or down to compartment outside under drivers seat..
May want to drop out dash face mounting boards to see behind dash.

[Skip426]

Look closely at the wires to see if they are labled in any way, a lot in my 99DSDP have printing on them. I am in the process of registering for access to wiring diagrams, so I can't be sure BUT the dash light wire may go through the firewall to the fuse/relay panel ( dedicated fuse) and then back to the instruments. My coach is in storage so I can't even check under my dash. If I get a diagram I'll post more info.
If the reostat blows the problem would be between the headlight switch and the fuse panel.

["007"]

You can get general wiring layouts in the Com. Net link.
The newer wiring harness's do have print on wires indicating what wire is for and where they go.

[prpickett]

Tracked down the wire, which branched to 7 wires and then 2 more. One of the wires is definitely grounded, ended up going to the Stewart Warner control box (model 988C). It was one of the wires in a bundle labelled voltmeter, which is odd, because this isn't the wire bundle leading to my dash voltmeter. The only other wire that was "grounded" goes to the heater controller light on the dash, but this one is showing 12 ohms to ground which is probably about right for a light. Trying to locate a diagram for the Stewart Warner box now so I can figure out what the resistance should be.