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Unread 11-25-2014, 04:58 PM   #1
esterelyj
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1989 YJ Wrangler 
 
Join Date: Oct 2014
Location: Esterel, Quebec, Canada
Posts: 49
4wd light is always on

My 4wd light is always on. My 4wd system works just fine in all ranges including 2wd. When i put my headlights on the light goes out. Any ideas?

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Unread 11-25-2014, 05:01 PM   #2
mike134
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1989 YJ Wrangler 
 
Join Date: Aug 2014
Location: Cleveland, OH
Posts: 1,305
That's strange. Sounds like a grounding issue if it turns off with the headlights.

I think the consensus is that it doesn't really matter if your front axle doesn't disconnect, if that is the case. It just costs a bit extra gas mileage.

If you want to ensure your front axle is connecting/disconnecting, just get underneath and do the vacuum tests.
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Unread 11-25-2014, 05:07 PM   #3
silleYJ
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1988 YJ Wrangler 
 
Join Date: Sep 2013
Location: Colorado City, Texas
Posts: 19
I don't know for sure but this is what I would check if I were you. Your 4wd light is operated on a vacuum, if it is always on then your vacuum switch is hooked up wrong and is on a constant vacuum. Or you are always in 4wd. It is a small blue(or at least mine is blue) diaphragm looking thing that should be on your firewall by your battery box. I would check to see if it is always on a vacuum or not, if it is then the switch is probably not hooked up to your shift fork via the correct vacuum lines. The only other thing I would check is pulling your instrument cluster and clean it with some electric contact cleaner and make sure there is nothing shorting it out and it doesn't get enough power when your headlights are on.
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Unread 11-25-2014, 06:43 PM   #4
fishadventure
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1991 YJ Wrangler 
 
Join Date: Jul 2013
Location: Morrisville, VT
Posts: 969
I don't think it is electrical. Mine did that (oddly) when the pretty multicolored vacuum lines cracked. I found it went out when under full throttle which didn't make sense to me (low vacuum?!!) but I didn't care so I sealed the vac line and pulled the bulb. Probably didn't need to pull the bulb. Dunno. But it's not on anymore but I have a homemade posilock cable. If you are using the vac operated disconnect this won't work for you.

There are two kinds of 4x4 light switches: one is a vac switch (like mine) and the other is switched at the vacuum motor by a mechanical switch that depresses when the motor moves. Either way I think the switches merely ground the powered bulb to illuminate it: I think, not sure. So it could be a chafed wire, a stuck plunger switch, or a vacuum switch issue.
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Unread 11-27-2014, 07:21 PM   #5
esterelyj
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1989 YJ Wrangler 
 
Join Date: Oct 2014
Location: Esterel, Quebec, Canada
Posts: 49
Thanks for the replies. This will help me figure it out i think.
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Unread 11-28-2014, 10:16 PM   #6
caain
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1987 YJ Wrangler 
 
Join Date: Aug 2014
Location: Grand Junction, Colorado
Posts: 13
I just wired mine back up with the OP's posi-lok system this week so the 4WD light would start working. It is a grounding wire that goes from the bulb in your dash to the blue-ish vacuum switch on your firewall. The wire is black with a yellow stripe (on an 87 at least). There's a yellow one with a black stripe in there too - leave that one be.

I think fishadventure is on the right track though - and I'd lean more towards a chafed wire or dirty contacts making the wire ground out. If it's always on, I doubt it's an issue with the contacts in your dash. Several of them share +12v connections on the flexible PCB board behind the bulbs, but they all have independent ground circuits (as this is how they light up). If it was a short behind there, the 4WD light would only come on when another bulb had good ground (seatbelt, brake, etc.).

Hopefully it's something simple, but a posi-lok kit wouldn't be a bad idea if need be.
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