Hi all my rear window demister has not worked since I got the truck and with winter on the way again I would like to get it sorted. I have power to the switch and power out but nothing at the rear window. I have been trying to find where the relay is as I suspect this is the culprit. Does anyone know where it's located? ?
Bj74 rear window demister not working (1 Viewer)
- Thread starter 88 land tank
- Start date
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Have you checked for power at the terminals at the window? A lot of times the grids break apart but most times it is hard to see. Be careful you don’t end up blowing out the window.
I would also check where the wiring goes into the door.
- Thread starter
- #4
Yeah I've checked both Windows at the terminals and one side had half a volt and the other .8 of a volt. That's why my guess was the relay but I cant locate the dam thing.
- Thread starter
- #5
Hi rosco the wiring that goes into the door looks to be in good condition as I've checked and taped my speaker wires to the harness
Hello,
Your defogger wires may be broken.
With the ignition switch in ON, turn on the defogger.
Wrap some tin foil in the negative tip of a multimeter and press it with one finger against the vertical section of the window wiring.
Then measure the voltage of the horizontal wires, placing the positive multimeter tip in the middle. If your multimeter reads 0 V or 10 10 V, then the wire is broken. If the multimeter reads approximately 5 V, then the wire is good.
Move the negative tip to the broken section of the wire and continue measuring voltage to pinpoint the damage location.
Use conductive paint to repair the broken wire. Electronic supplies stores are your friend.
Juan
Your defogger wires may be broken.
With the ignition switch in ON, turn on the defogger.
Wrap some tin foil in the negative tip of a multimeter and press it with one finger against the vertical section of the window wiring.
Then measure the voltage of the horizontal wires, placing the positive multimeter tip in the middle. If your multimeter reads 0 V or 10 10 V, then the wire is broken. If the multimeter reads approximately 5 V, then the wire is good.
Move the negative tip to the broken section of the wire and continue measuring voltage to pinpoint the damage location.
Use conductive paint to repair the broken wire. Electronic supplies stores are your friend.
Juan
Hello,
I forgot something.
The voltage values above are good for a 12 V system. A BJ74 is likely to have 24 V electrics. My guess: values should be higher. Maybe 0 V / 20 V for a bad wire, around 10 V for a good wire.
Not entirely sure about it, though.
Juan
I forgot something.
The voltage values above are good for a 12 V system. A BJ74 is likely to have 24 V electrics. My guess: values should be higher. Maybe 0 V / 20 V for a bad wire, around 10 V for a good wire.
Not entirely sure about it, though.
Juan
- Thread starter
- #8
Hi would that be why there's no voltage in the wires that clip to the glass? When I disconnect the wires to the glass and test with a multimeter that's where I get my 0.5 volt reading
jblueridge
SILVER Star
I did not see a relay shown in the wiring diagram.
I can't be 100% sure this is the right diagram tho'.
page 4
I can't be 100% sure this is the right diagram tho'.
page 4
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- #10
Hi yeah that's what I found to but there must be one somewhere as I havnt seen a demister setup without a relay yet??
I'm 99% sure that he switch handles the current. No relay on my PZJ75....
Do you have a demister on the rear window? I haven't seen that on an Australian model.
I could not find a relay after a 10 minute look.
Hello,
A 0.5 V reading suggests the wire is broken somewhere.
There is no relay in this circuit.
Do you have the problem on both windows? Sometimes the wiring on one windows breaks while the other is still functional.
Juan
- Thread starter
- #14
OK so may be the bj74 is the same?
- Thread starter
- #15
Yeah it does its a Japanese import maybe that's the difference?
- Thread starter
- #16
Hi yeah its both Windows not working. Maybe a dodgy switch? It does have power coming out of the switch tho?
Hello,
Voltage in the defogger switch reads around 12 V if I remember correctly. The little bulb inside the switch should read around 12 V as well -yes, I tinkered with that bugger for curiosity's sake. I might be stating the obvious here, but for a BJ74 it should read around 24 V (the BJ74s I have seen were all 24 V.)
If the switch does provide power, you should check the wire connectors in both doors. I just remembered they corrode over time and lose contact. Clean them and measure voltage. If there is no voltage, check the harness for continuity. Otherwise, check the wires.
Hope this helps.
Juan
Voltage in the defogger switch reads around 12 V if I remember correctly. The little bulb inside the switch should read around 12 V as well -yes, I tinkered with that bugger for curiosity's sake. I might be stating the obvious here, but for a BJ74 it should read around 24 V (the BJ74s I have seen were all 24 V.)
If the switch does provide power, you should check the wire connectors in both doors. I just remembered they corrode over time and lose contact. Clean them and measure voltage. If there is no voltage, check the harness for continuity. Otherwise, check the wires.
Hope this helps.
Juan
