Need some help with electrical diagram (rear defogger)

[nelliott500]

My rear defogger doesn't work. I've been troubleshooting things over the course of a few days. Switch is good, relay is good, timer works on bench, connections on rear windshield are good now (had to resolder the ground). I now know 100% what my problems is but not why it exists.

The problem is with the defogger timer when installed in the car. Bench testing works fine. The issue is that pin 5 on the timer is not getting 12v like it's supposed to. With the key off, I have 0.14v draw on pin 5. With the key on, I have 2.28v. With key on/running lights on, I have 2.25v. With key on/headlights on, I have 2.23v.

I'm so confused. I'm supposed to have 12v there but I don't know what the source is because I don't understand enough of the wiring diagram. I know this is my problem because I ran a quick auxiliary 12v connection to that pin on the timer and, when I hit the switch with the key on, the relay clicks and I get 11v at the defogger connection on the rear windshield (should it be 12v?).

Can someone help me figure out where the 12v for pin 5 comes from? I just don't understand the diagram.

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[okm12346]

pin 5 on the timer is on ground. at least thats what the diagram says.

The whole idea is to have continuity between pin 1 and 2 on the timer for 11 seconds. You say you tested the timer then it doesnt get one or two of the input signals.

Pin 1 should be always 12V with the switch depressed
Pin 2 should be ground with the switch depressed
pin 4 should be 12V with the switch pressed
pin 5 should be something, but if you pull out the timer, the pin on the harness should read ground
pin 6 is a signal from the alternator. Im guessing here, but to me it looks like the timer shouldnt come on if the engine isnt running (no voltage from alternator)

 

[nelliott500]

Sorry, I was referencing pin 5 on the actual timer page. I've noticed a few inconsistencies between the wiring diagram and the individual pages for each component (timer, switch, relay, etc).

So, pin 6 is a signal from the alternator. I'll be honest... I haven't tried it with the car running. It never even occurred to me that it would be necessary. I'll kick myself if I've been doing all of this troubleshooting for nothing. My original fix of resoldering the ground at the rear windshield probably fixed everything... I have to go give this a shot. I'll report back shortly.

UPDATE: Holy shit. Unbelievable... I wasted a few days trying to track down this issue and it's simply because the car had to be running. Unreal. I get ~13.5v at the connector after I press the switch while the car is running.

Well, I really appreciate the help. I don't think I ever would have figured that out. It also didn't help that I was using the pin numbers from the timer page and not the actual diagram.

Thank you.

 

[okm12346]

haha, no problem.

 

[nelliott500]

Now that I think about it, should I be worried that I have a slight draw (0.14v) from that pin with the key off?

 

[okm12346]

When you flip the switch, the power to the time controlling components in the timer is off. The only thing that comes to my mind is maybe an internal capacitor in the timer, or voltage drop on two diodes (0.7V+0.7V). If it doesnt affect your battery overnight then theres nothing to worry about.

If you really want to know if there is current draw between pin 5 and ground, you need to have the wire cut and hook up the DC amp meter between the two ends.

 

[nelliott500]

Good enough answer for me. I've had the car sit for close to two weeks and it turned on just fine so I won't worry about it. I really appreciate the help.

 

[DSM1G90]

Ya. we don't want to see you have a serious battery drain pushing the defrost button in without the motor running-not a good manufacturer practice. Takes quite the amps to send current through the wires on the glass.