rheostat question

[jim 56]

Hi just took apart my dashboard rheostat for dimming.From a previous owner he must have taken the wires off because it didnt work.Does anybody out there know where the wires come from and where do they go to?

[Aaron h]

The dash light rheostat gets it's 12v+ supply from the round electrical plug above it, but through the printed circuit board.  There are no wires. It's all integrated within the printed circuit board.  When you remove the rheostat there will be two metal pins sticking up out of the printed circuit board that the rheostat slides on to.

If the rheostat ends up being bad you can still find them, but they're stupid expensive.  I've often seen people solder a wire between the two brass legs on the rheostat as a cheap fix.  You won't have the ability to dim the dash lights any longer, but you'll have lights.  Then again, it may just need to be taken apart and cleaned.  If the spiral wound resistance wire inside of the ceramic housing has com loose then it's pretty much a hopeless case for repair.  That happens often, as well.

[jim 56]

Thanks yea I just saw the pins.Mine should work I cleaned it up.Now I got to try and find which wire from the round plug power comes thru.Thanks for your help.

[Aaron h]

You must get yourself a proper schematic so you can make these determinations much easier!  

Below is a picture of the instrument cluster electrics.  The lowercase letter "g" at the top are the instrument cluster light bulbs.  If you'll follow the common power supply down, you'll see that it comes out of the rheostat, denoted as "f".  The power supply then exits out of the rheostat at circuit 58d. Following that wire over to the left you'll see that the color is gr/bl.  (gray with a blue tracer).  Hope this helps. 

[jim 56]

great thanks I see it now.I have them working on the bench.Thanks again
Jim

[yves]

 If it can help :

[Peter van Es]

Yves,

your pictures are very helpful. But as you post them as Google Pictures, if you lose your account / delete the pictures / Google changes its policy, our forum will have broken links to empty pictures. Don't think that will not happen, we had a whole bunch of pictures linking to a free picture sharing service. They changed their policy, started charging money, the original poster had left us, we had no access to the account and we now have a bunch of dead links.

That's why we recommend for people to attach pictures to the post, or upload them to the Tech manual. That way they are on our servers, and we don't lose access to them. Attaching a picture is simple: when in a post, click the '+' "Attachments and other options" button under the post window, and add up to four attachments.

[FGN59]

Yves,
How did you clean the coil, and what kind of glue did you use to fix it?
Thanks.

[mdsalemi]

...If the rheostat ends up being bad you can still find them, but they're stupid expensive.  I've often seen people solder a wire between the two brass legs on the rheostat as a cheap fix.  You won't have the ability to dim the dash lights any longer, but you'll have lights.

By modern standards, the brightest setting (full voltage) of the dash lighting with the rheostat turned UP or bypassed by said jumper, is painfully weak.

There are so many more things (on these cars) that you could and should spend your time (and or money!) on than this one.

[Aaron h]

By modern standards, the brightest setting (full voltage) of the dash lighting with the rheostat turned UP or bypassed by said jumper, is painfully weak.

There are so many more things (on these cars) that you could and should spend your time (and or money!) on than this one.

That's usually the case, but if all new bulbs are installed it's not too bad.  While a bulb may still work, it may have a substantial amount of tungsten migration.  This is when the bulb turns black.  The tungsten filament leeches the tungsten off of it over time, and it hits the glass causing the black color to form, which makes the bulb dimmer than it should be.  LED bulbs are a nice thought, but only if the color temperature is between 2,700 and 3,200.  LED bubs still have a long way to go before they're able to emit light in a full peripheral like the incandescent bulbs do. 

[jim 56]

I cleaned the rheostat and put in 5 watt bulbs.I left it on the bench hooked up to a battery for about six hours.It is pretty bright and I didn't notice any extra heat.Will install in car today.Thanks for all the help.

[yves]

To FGN59 i cleaned the coil with chlorhydric acid  HCL  and glued in place with époxy .
To Peter i tried to post photos with the forum atachments but it doesn't work…. even if i use pics in a low pixel definition. May be i Don't do the right process?

[FGN59]

Merci for the tips!

My rheostat is also 'jumped', not sure I want to change that (not sure I want to get into the dash unless absolutely necessary), but in case I end up in there, now I know what to do and how to do it. Thank you!

[yves]

  I have "refitted" the jump …!  anyway there must be not a big difference at night and i Don't want to go in the cenyral cluster dash soon...

[clunker]

Tech Manual updated with section on installing (warm white) LED bulb replacement and necessary resistor - https://www.sl113.org/wiki/Electrical/InstrumentLights