Power seat problem

[tech_ed]

I have an 89 Wagoner LTD (the Cherokee style) that came with everything...including power seats. All at once, the power seats no longer work. I checked the fuse (it's a 30 amp breaker) and it is still good (I temporarily replaced it with a 25 amp fuse). What troubles me is that BOTH power seats are not working. I could understand if one wasn't working, then it's a switch or motor problem. But both front seats are dead. Is there a relay that sends power to both seats after the fuse or some common power lead?

I found a black and a red cable that is joined, under the seat with a molex connector. I disconnect this connector and measure the voltage and I get 12 volts across this.

Anybody have any hints on how to track this problem down?
Thanks
Ed
web/gadget guru

 

[XJNick]

Well, the schematic I looked at shows no relays. The motors are driven through the switch. It sounds like you might have an open ground that is affecting both seats. Put a meter between the power from the incoming hot to the seat ground wire, should get a reading.

-Nick :!:

 

[tech_ed]

Thanks for the heads up. I didn't get a chance to try this yet (non-stop rain)
OK, just so I get this right.
The motors are connected to ground? If that's the case, why are there positive and negative leads going to the switch?
I suspect that perhaps the motors are run forwards with the wiring in one direction and reversed by switching the power around (standard on DC motors). Given this, the motors would need to be isolated from ground, right? (the same way that the power locks work...)
This is what's bothering me about these power seats...I can't identify how the power is distributed. Seems that the positive and negative wires (they run under the carpet so I can't be too sure) run to each seat seperatly. So this means that they gotta be coming from some kinda distribution point.
If I test the voltage across these two wires, I get 12 volts. Potential across the red wire and ground (a bolt holding the seat to the floor) I get 12 volts. Potention across the black wire and ground is zero.

Now for the really weird part. Both the red and black wires run to the seat switch. If I peirce the insulation on these two wire I measure 12 volts. While measuring this voltage, if I actuate any of the power seat controls, potential across these two wires drops to zero.

Any clues???
Thanks

 

[XJNick]

You are correct. The switches change the polarity of the power to the motors in order to turn them either direction. What i meant was, and I think you verified this?, is there continuity between the hot input to the switches and the switches' ground wire? If you have a good power and ground input to the switches, and the motors aren't working, I'd suspect bad motors or switches.

Hope this helps
-Nick :!: