Take a look at this image,
http://www.walt-n-ingrid.com/0X280010.jpg
My truck has a lift kit so yours will look slightly different. Look at the
connection just behind the tie rod end in the image. If the end of the wire
looks like this then it is the wire for the 4WD lamp in the cab. It's a
plug with 2 wires that connects directly to a switch on the front axle. The
front axle has a Central Axle Disconnect or CAD. The CAD works sort of like
an automatic hub and on an 87-90 Dakota works completely by vacuum. There
are two vacuum lines that connect to a small round canister on the front
axle that looks kind of like two small pie tins pressed together. You can
see it on the left side of this image.
http://www.walt-n-ingrid.com/0X150003.jpg
The other end of the vacuum lines run to a switch on the transfer case. If
you look under the truck, you'll find it to the rear of the transfer case on
the driver's side of the truck. It will have 4 vacuum lines connected to
it. Two lines for the front axle, one from the engine and one to a ball
canister connected to the underside of the bed.
All the wire with the plug on the front axle does is turn the 4WD lamp on
and off. It is very common for the vacuum actuator on the front axle to
stick.
Here's how to test it:
Disconnect the two vacuum lines from the front axle. With the truck running
and in two wheel drive you should have vacuum to only ONE of these two
lines. Make a note of which line has the vacuum. Now shift the truck into
4Hi and recheck the lines. The vacuum should change to the OTHER line. If
it does not, the switch on the transfer case is bad and should be replaced.
If I recall correctly, it will cost around $30-$40 at the dealer. It's kind
of like an oil pressure sending unit and will screw into the transfer case.
It has a small metal ball on the threaded end and when the transfer case is
shifted into 4WD, something inside the transfer case pushes in the metal
ball and changes the valve inside the unit.
If the vacuum does change from one line to the other, the actuator on the
axle is stuck. Like I said earlier, this is very common. You can try to
loosen it up by spraying some WD40 into each vacuum tube the lines connect
to. Don't be shy, really try to flush the crud out of it with the spray.
Reconnect the lines and drive the truck forward shifting in and out of 4WD.
Repeat the process rolling backwards. If it doesn't come loose, you will
have to replace the actuator. Once it is working, repeat the flushing
process about once every six months to prevent it from happening again.
Remember, if the wire is disconnected, the 4WD light will not come on.
There has to be a reason why someone disconnected it. Watch for blown fuses,
unusuall power drains, etc.. Also, sometimes when in 4WD, if you shift back
into 2WD, the front actuator will stick. Usually happens in cold weather.
The transfer case will be in 2WD but the CAD is still locked and the 4WD
light will stay on. Shift the truck into reverse and back up about 15-20
feet. That will usually pop it loose when stuck locked.
Walt Felix
88½ Dakota Sport 4x4, 2000 Ram 1500 QuadCab Sport 4x4 and a 67 Barracuda
Coupe 340/4Speed
Walt@Walt-n-Ingrid.COM
http://WWW.Walt-n-Ingrid.COM
http://WWW.MoparsinMotion.COM
----Original Message Follows----
Date: Thu, 28 Dec 2000 15:08:26 EST
From: ZaneDClark@aol.com
Subject: Re: DML: four wheel drive problem
The wire is attached on the front axle along with vacuum lines. My quess is
that this is the "lock out" for the front wheels to engage in four wheel
drive. I had the engine rebuilt and the 4-wheel would not engage afterward.
The wire is about 4 feet long with an obvious connector at the loose end. I
have looked for somewhere to plug it into but am at a loss.
I do have a Chilton book for my 90 Dakota, but find nothing for this.
I agree that no loose wires should be there. but where to plug into.
zane
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