Rear Defroster operation

[Evolution1980]

Strange thing this morning when I went out to my car...
I flip on the rear defroster ("RD") toggle switch. I hear the relay click and the light on the switch lights up.
However, I notice that my battery gauge drops about 2v and the battery light just ever-so-slightly started to illuminate.
I turn off the RD and the battery gauge goes back up to 14v.
Turn the RD back on...switch lights up, relay clicks, voltage drops.

Normally when the rear window has a coat of fog on it, the RD clears it up pretty quick. So much so that after about 30 seconds you can already see the heating strips starting clear the window. No such action this time. Got nothing but the observations just listed.

I didn't have a chance to check actual voltage being drawn with my multimeter, but I know that when the RD is working properly, it's never caused the system to drop 2v on the gauge.
The only other thing I can add at this point is that a few months ago, the switch stopped working entirely. Figured it was a fuse or something, but never got around to checking it. Then out of nowhere it just started working again a few weeks after that. ...Skip ahead a couple of months to now.

Ideas? ;help

 

[bill81vette]

Bad switch? or perhaps...hnoes a bad wire somewhere along the way!!!!
check the wiring at the RD to see if it is getting any juice or not.
I would check the switch as well as the fuse.


good luck!

 

[Vettehead Mikey]

What happens if you rev the engine slightly? Might simply be the alternator belt slipping.

Nothing wrong with the switch if it's causing a draw on the system when it's supposed to.

 

[Evolution1980]

check the wiring at the RD to see if it is getting any juice or not. I would check the switch as well as the fuse.

Bill, I would think that if it's a bad switch or fuse, I wouldn't see the switch light up, hear the relay tick, nor see a voltage drop. No?

What happens if you rev the engine slightly? Might simply be the alternator belt slipping.
Nothing wrong with the switch if it's causing a draw on the system when it's supposed to.

If I recall correctly, I did rev the engine and there was no change as far as what I saw on the volt gauge. I did have a slightly loose belt earlier in the season, but tightened it up. I'll check again when I remember, but I doubt it's loose.
As far as a voltage drop during proper function, I've never noticed it drop 2v (on the gauge) and cause the battery light to illuminate. Nor should it.

Hmmmm....

 

[Vettehead Mikey]

I was saying the switch was not faulty by causing an amperage draw, there are possibly other evil things lurking.

If your voltage does not increase to 14-15 V at higher engine speeds then a weak alternator might be the cause.

 

[Evolution1980]

I was saying the switch was not faulty by causing an amperage draw, there are possibly other evil things lurking.

If your voltage does not increase to 14-15 V at higher engine speeds then a weak alternator might be the cause.

Ahh..gotcha!

 

[73shark]

Could be bad contacts on the switch and/or relay which could be causing all of your voltage to be dropped there instead of the RD.