A little electrical help please

[Edward B.]

Guys, I was working on my rear defogger switch last night and I dropped it, shattering the little ceramic "thingy" (see the example in the attached picture I stole from Google).

I'm assuming this is some kind of resistor (?) on the "low" side of the switch to lower the 12VDC voltage going to the blower motor to something like 6VDC, but I'm not positive about that.

Either way, no matter what it is, I would also assume that NO ONE will have that exact same part anymore, so does anyone know of an equivalent?

Thanks
Ed

[Tom L.]

Re: A little electrical help please

My '72 does not have the ceramic thingy, just three wires. Feed, high and low. Do you have a three wire switch? And that is a tough devil to find.

[Edward B.]

Re: A little electrical help please

No, my switch has two spade connectors that the wire harness plugs into. I've attached a (lousy) picture of it that I took a few years ago. It's a little out of focus, but you can see the two spade connectors and the ceramic "thingy" underneath. The wires inside the ceramic "thingy" are just wound around inside and one side is attached to one of the spade connectors and the other side is attached to a 3rd terminal as shown in the other picture I stole from Google!

Ed

[Michael H.]

Re: A little electrical help please

That round thingy is a resistor see if you can measure it with an OHM meter. Is there any makings on the "thingy" showing wattage ?

Mike

[Edward B.]

Re: A little electrical help please

Mike, there MAY have been something stamped on it originally, but now that it's in a million little pieces, I can't tell. I'll see if I can get a resistance measurement this evening when I get home.

In the meantime, does anyone have a spare they can look at to see if it has any markings? I would imagine it'll have an ohms stamp, but hopefully it'll have a wattage or amperage stamp too. If it does, I can find a replacement at Radio Shack (IF they've not gone out of business by then!)

Ed

[Michael H.]

Re: A little electrical help please

Ed,

What year car are we dealing with ? Where is this part located ?

Mike

[Edward B.]

Re: A little electrical help please

Mike, it's a 1969 roadster and the switch is in the driver's side front console trim panel.

Ed

[Michael H.]

Re: A little electrical help please

Check this out maybe the guy selling it will tell what's on the resistor............

http://www.ebay.com/itm/1967-Chevrolet-Camaro-Rear-WIndow-Defogger-NOS-GM-Chevelle-Nova-Impala-/272140429065

Mike

[Edward B.]

Re: A little electrical help please

Thanks Mike!! I just sent him an email.

Ed

[Joe R.]

Re: A little electrical help please

Ed,

Once you know the resistance, you can guess the worst case wattage. Assuming that full battery voltage would be the most it would see across it.

P = V*V/R (power = voltage squared divided by resistance)

Maybe use 16 Volts for maximum worst case battery voltage.

By the way, Mouser and Digikey web sites allow you to choose a resistor (or other electronic part) based on what you know using filters.

Joe

[Edward B.]

Re: A little electrical help please

Well, I emailed three guys on ebay and two of them replied so far. Unfortunately, neither resistor had anything written on them so that was a dead end. However, one of the guys measured his and he said it was about 6 ohms. I measured what was left of mine and got just over 4 ohms, so I'm not sure why they're different.

So Joe, going by your equation, 16x16=256. Divide this by 4 ohms and I get 64 watts. If I divide by 6 ohms I get 42.6 watts Maybe I should get a resistor that's in the middle of the two measurements (approx. 5 ohms)? Or would you go with the 4 or 6?

Ed

[Joe R.]

Re: A little electrical help please

Hi Ed,

Well, I was illustrating the worst case, which would be full battery voltage across the resistor. Can you measure the actual voltages across the resistor in all switch positions with the engine running? Please also measure the battery voltage and post that here. When measuring a small resistance like this, the meter lead resistance is significant and needs to be subtracted off the resistance reading displayed by the Ohmmeter. Did you do that? I would use four Ohms to be on the safe side. It's best to be very conservative with wattage ratings. If you can provide the info I requested, I'll be happy to help you pick out a resistor if you like.

Joe

[Edward B.]

Re: A little electrical help please

Thanks Joe. I'll get you those numbers later on this evening.

Ed

[Joe L.]

Re: A little electrical help please

Guys, I was working on my rear defogger switch last night and I dropped it, shattering the little ceramic "thingy" (see the example in the attached picture I stole from Google).

I'm assuming this is some kind of resistor (?) on the "low" side of the switch to lower the 12VDC voltage going to the blower motor to something like 6VDC, but I'm not positive about that.

Either way, no matter what it is, I would also assume that NO ONE will have that exact same part anymore, so does anyone know of an equivalent?

Thanks
Ed

Ed------

This is a part that you don't want to need. The original switch was GM #3942696. It was replaced by the 1971-73 switch, GM #3998399. The latter was discontinued without supersession in 1986 (i.e 30 years ago). As far as I can tell, this was a Corvette-only piece. These factors do not bode well for finding one.

My suggestion: if you could find a defogger switch from another Chevrolet model in the 1968-75 time period, you MIGHT be able to salvage parts of it for repair of your switch.

[Edward B.]

Re: A little electrical help please

Joe L - Yes, these switches are actually fairly easy to find (there are a few on ebay right now), but for some reason the owners think they're made out of gold, so the prices are ridiculous. I refuse to pay $200 for a stupid switch!

Joe R - I also posted a request on the Camaro site and one of the guys there said The original blue block resistors read out between approximately 4 to 6 Ohm's and are rated at 5 or 10 watts. So with that info, what would you suggest?

Ed