Dimmer Switch testing with OHM Meter

[CudaHead]

I'm working on changing out my standard dash on s 1970 Cuda, to a Rallye Dash.
I have four dash dimmer switches. I'm trying to OHM them out to see if they are ok.
It seems to be an easy thing to do but all four show the same thing, no connection.
The wiper is touching the coiled wire on all of them.
I connect to the center lug, which is the voltage feed. Then to the one tied to the wiper arm. Move the dial and I get nothing (open).

Am I missing something? Are all four bad?

[Cuda Cody]

A resistance ohm test should work to test them.  I doubt 4 of them are all bad.  Post of photo of your switches if you can.

[CudaHead]

Pictures of the switches.

[gzig5]

Stupid question but I've been bit before.....the Ohm meter has been verified to be working correctly?  An analog one needs a good battery.  Interested to see what you find.  My dash lights don't work at all and I need to start poking around.

[Chryco Psycho]

What scale are you using on the Ohm meter assuming it is not auto ranging you want 0-100 ohm
Do you have continuity end to end on the coil ?
@slotts will be able to help you

[GoodysGotaCuda]

Continuity does not ensure it can carry any load. Putting a load on it and performing a voltage drop test is the best method to see which switch is in the best shape.


For example, a single copper wire can go from your battery to your starter. If you ohm it out, it will have perfect continuity and very low resistance at that. However, it'll melt and not carry any load as soon as you hit the key.

Continuity is one thing, load capacity is another.

[CudaHead]

I always check the meter before using it. I set it on a low ohms setting and short out the leads. The part about the batteries being low is interesting. I have serval meters and I used two of them to do this test.  Same results but I will put in new batteries and test again and let you know.
I found out that I have two more of these in clusters setting around. I will test them also.
One of those looks like it been messed with, so I will try to pull it apart and see what I am missing.
The problem appears to be between the outside lug to the inside wound wire.

[CudaHead]

Ok, I changed  the battery and got the same results.
I tried to take it apart but I can not get that spring washer on top to come off.

In my testing I tested from the center lug where we get the battery supply, to the ring in the top of the photo to the down turned lead of the ring.
Center lug to ring show connected.
Center ring to the down turn on the ring is not connected.
Ring to the down turn is not connected.

[CudaHead]

Anyone know how to get that top spring washer off the back side?

I see replacement in my Au-ve-co catalog under part number 8862.
BTY, I recommend everyone get this Au-ve-co catalog. It has just about every automotive fastener in it. You buy boxes of them for almost the same price as local auto parts stores charge for single ones in packages.

Also anyone know where I can get that part shown in the Picture?

[Cuda Cody]

All you should have to do is clean the connection where it touches / glides along the coil and you should be able to get a test (ohm) result.  I tested a few old ones in my shop and they test fine with the ohms (the ohms adjust as I turn the knob).  I bet it would test better with power, but I always clean my up before I use them and then test them.

[CudaHead]

Ok, I know how it works now and what has to be done.
The ring in the picture above, turns with the knob.
The back plate has a ring on top of it that connects to the power feed lug.
They slide on each other as the knob turns.
They are corroded and do not conduct between them now.
It tried to clean them up with electric cleaner spray. It did not help.

How to fix:
The back plate has to come off. It has a spring washer holding it down.
The moving ring and the non-moving ring need to be cleaned.

[CudaHead]

OK, I got it apart and cleaned everything. It was not pretty but it got done.
Put it back together. I found I had the keeper nut and it worked to hold it together.

Guess what....it works now.
 

[CudaHead]

I tested all of my dimmer switches and they all have the very same problem.

[CudaHead]

 I had serval of these switches that had the same problem with oxidation on the top two rings that slide on each other ( not the wound wire ).
I ordered this off the Internet:   DeoxIT

https://www.amazon.com/Hosa-D5S-6-DeoxIT-Contact-Cleaner/dp/B00006LVEU/ref=asc_df_B00006LVEU/?tag=hyprod-20&linkCode=df0&hvadid=198057017270&hvpos=1o2&hvnetw=g&hvrand=10823363549277153421&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9011007&hvtargid=pla-382003658380&psc=1

They started working. No disassembly required.

[73440]

@CudaHead , thanks for tip on tge Au-Ve-Co catalog , downloaded it for future use.