Rear defroster draining massive power, any common problems?

[destrux]

Like the title says, are there any known problems with the rear defroster/defogger? Mine works, but when I turn it on it drains so much power that the car will shut off after a few seconds. The second I turn it on the voltage gauge goes from 14 to 11 and keeps going down till 9V and then the car stalls and everything resets (or till I shut the rear defroster switch off). I stopped using it, but now with cold weather coming back I need to fix it.

I checked the grid for opens/shorts and found nothing. I would think that if it was drawing too much power from a short that it would blow the fuse... :aigo:

 

[Poodles]

Also heats the mirrors...

 

[GrimJack]

I've had the plug on the hatch side near the hinge go. Open the hatch, pull the hatch side rubber housing out, then wriggle the harness out until you can see the plug. Mine was obvious - badly burned, all brown and ugly. Disconnecting the plug was near impossible. If you have a partial short to the body, it might pull enough current to cause problems without popping the fuse.

On the other hand, it's also a rather large current draw by design, and if your alternator or alt grounds are weak, it could easily pull it over the edge.

 

[destrux]

Thanks I'll check that.

I found another weird thing, I was testing the amperage output of the alternator and when I turn the defroster on the alternator stops charging completely, then resumes normal charging when the switch is turned off. The alternator is putting out 14.59V and charging amps are perfect (12A at idle, no acessories, 47A with fan on high and high beams).

I'm going to re-check the grounds on the whole car (checked them a few months ago). I have a 1.0V drop between the battery and the ECU, according to the volt gauge on my AFC Neo. I think there's a bad ground somewhere.

 

[Flateric]

I'm sure that this is an uncommon problem but back in 87 when I owned a 86 celica my rear window defroster had a very serious issue that eventually forced the total replacement of it under warrenty. It went like this......

One day after starting the car to warm it up on a particularly cold day I was walking back out to it to go to school and put my hand on the window as I went around the car. The palm of my hand got burned badly! The window was heating up so much, right where the two wires clip onto it, that it literally sizzled if fresh water drops landed on it. I knew this couldn't be normal so, still being under warranty I took it too the dealership and let them know. They didn't see it as a problem and sent me back on my way. Winter got worse and I complained about this issue for the next 3 times I brought the car in. They always told me it wasn't unusual. Then........

On a particularly cold morning I was on the highway going to school when suddenly my rear window literally exploded instantly. My first thought was......OMG someone is shooting at me! I pulled over to the side of the road and had a look at the damage. You could clearly see that the window had exploded from the exact spot that I knew it was getting too hot from. All cracks clearly began from this point. Nearly froze that morning since I no longer had a rear hatch window. After school I took the car back to the dealership and complained again that this was the cause.

They had no choice but to agree. It seems the window had some type of flaw that was drawing huge amounts of power and somehow shorting on the window directly between the two defroster hook up points. I also remember that when the defroster was on my lights would dim really easily, even music on the totally stock stereo system would induce a dimming effect with slight bass.

The alternator being new in a new car obviously handled it enough not to stall the motor. Obviously in a much older car like all of ours are this may not be the case anymore.

So turn on your defroster and make sure it's not getting stupid hot between the two contacts which would lead to abnormal power consumption and potentially and exploding window.

 

[destrux]

Holy crap. Well, I can't turn it on long enough for it to even get hot. I just unplugged the wires from the grid and it still does it, so that leaves the heated mirrors (which I had no idea my car even had, but there's a fuse in the box for it, so it must), or a shorted wire.

I also checked the plug in the top of the hatch and on the B-pillar and they're good. So far I've found no melted or corroded wires.

Edit:

Ok, so it's not actually draining more power than it should, because it's not even working. This is actually really stupid. The "how to wire a soarer 1JZ into an MA70" sticky told me to wire the purple (violet!) wire in the M1 plug (which comes from the defroster switch to the 7MGTE ecu) to the black/yellow wire from the IJ2 plug on the soarer engine harness, which goes to the 3 pin plug on the alternator.

The Soarer ECU doesn't have a pin for defroster idle up, so that violet wire just gets disconnected.

The black/yellow wire that it was connected to has to be connected to the black/yel wire in the old alternator plug that was cut off during the 1JZ swap. I have the wire wrapped up in the loom over there.

The defroster switch was dropping the violet wire to ground, which was eliminating the alternator "energize" signal, telling the alternator to stop charging.

After I fix this I'll see if my 1.0V drop went away, but I think that might still be a bad ground somewhere, or a dirty ignition switch.

This whole thing started off as me checking for electircal problems because I noticed the ECU was only seeing 12.5V with the car running sometimes, and it would misfire if the voltage was below 13.5, getting worse as it went lower. I'm trying to get ECU voltage up to the 14.5 I'm seeing at the battery.

I really could care less if the defroster works, I never use it. I just hate misfires.