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Hot rheostat [dimmer?]

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Sam

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My rheostat was broken when I bought my 1980 MGB. The instruments were very dim. I found a used replacement, and popped it in without too much difficulty. I've noticed that the switch (not the knob, but the switch behind the dash) gets VERY hot when in use. It too hot to hold onto for any length of time. I don't think it'll melt the plastic though.

Is this a problem?

A little confession before we go on... Before replacing the broken rheostat, I put Type 50 (Radio Shack) bulbs into the instruments to make them brighter. The blub is 7.5 V.

I got this bright idea (no pun intended) from https://www.mgbexperience.com/service/tips/interior.html

Would this be contributing to my issue, or do they always feel hot?

Thanks,

Sam
 
That's how rheostats work. They bleed off the "extra" electricity in the form of heat. Imagine that the rheostat is like a little toaster. Using non-stock bulbs may aggravate the problem as the rheostat has to work almost twice as hard. Don't worry about them though, they will burn out soon enough. Make sure nothing flamable is in direct contact with the device. bob

[ 03-31-2003: Message edited by: Bob Claffie ]</p>
 
Decisions, decisions.....bright bulbs...overly hot rheostat in a car with 4 fuses....

I'd go stock on the bulbs, thats why the rheostat is so hot. Plus, the bulbs may be getting hotter as well. Haven't seen a B melt the bulb housing, but see it a bunch on newer cars.
 
Thanks guys... that makes a lot of sense. I just need to solder in a spot for some eggs above it.
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Sam
 
I recommend putting in the correct voltage halogen bulbs, available from the Little British Car Co.

They made an amazing improvement in the brightness of my instrument lights. I can actually see them at night now. The halogens are expensive, but worth it, in my opinion. I've had them in my car for more than two years now. (And also put them in the tail/brake lights.)
 
You can also simply bypass the reostat all together by hooking both wires to the same side. Your reostat will not heat up because there is no power coing through it and you will have less resistance in the circiut to dim the bulbs. If you add the halogen bulbs from LBC, your gauges will be as bright as some modern American cars. Me, I did both!
 
Oh, I tried the Radio Shack bulbs, too, and they lasted less than two weeks before the first one blew. Within a month, all of them were out. When you put more juice through a bulb that it is designed for, you drasticly shorten it's life
 
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