hi all,

long-time lurker/searcher here but I can't find the answer to this one. My problem was originally a blown fuse on the TAIL. All running lights were out, as well as the instrument cluster lights. I did many hours of dismantling and running through everything with a multi-meter trying to track down a short on that bus. Eventually when I disconnected the instrument panel dimmer/rheostat the short appeared to be gone. What I don't understand is how the dimmer could be at fault here, so I'm trying to find out what the R values are for each end of the range on the dimmer. I'm assuming it goes from infinity at the lowest light setting and then slowly decreases in R to some measurable value that I can confirm.

Does anyone have the time to test their working dimmer??

This is a two wire rheostat and the only two ways I could see a dimmer fault causing this fuse to blow would be:

1. the dimmer is always supposed to limit the current, and the bulbs on the instrument panel would otherwise draw excess current and blow the fuse (i.e. if you bypassed the dimmer with a short wire the fuse would blow). this would imply the dimmer being bad by having too little R could cause the fuse to blow.
2. the instrument panel has a short somewhere and the dimmer is just allowing this short to draw enough current to blow the fuse.

Thanks in advance,
jesse

 

Were you trying to jumper the rheostat with battery voltage present??

It would blow the fuse when making the connection

If you made a poor connection it would open the fuse also .When the circuit was powered up..

The value of the rheostat should be on it most all the ones I work with have it easy to read .

You don`t always have access to a good one.

If I have time I will look.

 

I haven't tried jumping it but based on what you just wrote it implies that my case #1 is true. That the dimmer should always be limiting the current even on it's "wide open" setting. In that case if it shorted completely the instrument panel lighting could blow the fuse even without a short.

Very good to know! I will get a look at it. Yes, and let me know if you find out, too.

Appreciate the response.

jesse

 

You ever get this figured out ?/

Long week at work.

 

No sir. No solution yet. The truck was at the shop when I made the original post and I haven't had access to it since then!

However, they seem to have vindicated the rheostat. They found a melted wire, though.