Power seat Electrical issue

[MikeH1]

Hello, This is my first post, I hope someone can help me.
I have a 1990 Ford E150 van with the 5.8L, I have duel power seats which were working but are not now.
What I have done so far is check all connectors and secure all loose connections. I have checked power from the main power wire to the switches and from the switches to the connectors at the motors. which all have 12+Volts. I have run continuity on the switches and wiring, all seem good, so I have full power to everything, but the seats will not move. If I didn't know any better I'd think there was a bad ground but I can't find it other than the main ground wire at the switches themselves. So my question is, Do electric seats have a ground wire that should run from the frame of the seat to the van frame or metal floor? I'm at a loss as to why I have power to everything but no movement of either seat. Any suggestions are welcome at this point. Thank you.

 

[Dave9]

No. The seat switches are probably a two way switch which toggles the polarity of the power going to the motors to enable movement both directions, then the switch assembly has the lone ground point for it all.

Check resistance between the switch ground point and chassis ground. You may have wires fraying apart if not totally shot, anywhere rodents can get to it or from wear, particularly in the door hinge area where it flexes back and forth every time the door is opened. Could be ground, but an unplugged motor connector can read 12V across a very high resistance from a frayed power wire too. Consider the diagram below, the power and ground (at the motors) reverse roles based on switch position, though having them all fail at once does suggest the switch module ground.

You could try temporarily putting in a jumper wire between the switch module ground pin and chassis ground and if that works, might be as easy to just string a permanent new wire for that rather than track down the break, unless you find it with further investigation.

Here is a rough approximation of what that circuit could look like. This is NOT meant to be taken literally as far as wire colors, is not specifically for a '90 E150 van, though wouldn't be surprising if there was some if not all black on the ground wire:

 

[MikeH1]

Thanks Dave9, I appreciate the answer. I will try to find the ground from the switch, will have to trace back...not easy to do, this is a conversion van, and the more I dig into it, the more jury rigging I'm finding. I'm not sure if the conversion company hacked the wiring up or if the PO did it.

 

[mk378]

Put your meter from the ground wire on the switch to a known good ground (inside the cabin, I like to use the shell of the lighter socket.) Push the button. If voltage jumps up the ground is bad.

Are any relays involved, or is it just a switch and the motor?

 

[MikeH1]

Mk378, I will give that a try. I did run across a relay that has been wired in just in front of the fuse block i didnt check it because I have full power to the switches and motors, thats why I thought it might be a ground.

 

[MikeH1]

Mk378, I will give that a try. I did run across a relay that has been wired in just in front of the fuse block i didnt check it because I have full power to the switches and motors, thats why I thought it might be a ground.

That relay did not run to the power seats, The seats are powered by the battery with an inline 30amp fuse. All the grounds check out with no voltage running through them. I did put my DVM, on the line as I was testing the switches. I do have full power except when I push any of the power seat buttons, the voltage drops straight to zero volts, when I release the button it comes back to full power.

 

[wtd]

Since both seats no longer work it has to be a common power or ground that is bad. If you have power at the seat motor connectors than it's probably not a power issue and points more to a ground. If there is a relay for the seat circuit than it should be good if you have power to the seat motors. You really need a correct wiring diagram for your vehicle to see if there is some other circuit that you are not aware of that is also on the power seat circuit or some other component on the same circuit that could be pulling the circuit down.

I think you can get a day subscription or maybe a few days on Alldata for your vehicle so you can get access to wiring diagrams.

 

[mk378]

I do have full power except when I push any of the power seat buttons, the voltage drops straight to zero volts, when I release the button it comes back to full power.

That means there is a bad connection somewhere between the battery and where you are measuring. Move to the next part along the wire closer to the battery (the fuse) and do the same test there. The problem is going to be between the last place that has power all the time and the place where it goes away.

 

[MikeH1]

That means there is a bad connection somewhere between the battery and where you are measuring. Move to the next part along the wire closer to the battery (the fuse) and do the same test there. The problem is going to be between the last place that has power all the time and the place where it goes away.

MK378, WTD, Dave9

Thank you for your help in this matter. I got it figured out. The PO or whoever, ran all of the power wires for the seats right off of the battery with a 30amp fuse in between. I'm sure the Company that made the conversion did not run these wires in this manner, but it is what it is. I found that after back probing the connections all the way back to the battery, they were corroded, I cleaned them all up, reconnected and I have full power back to the seats. Now I just have to figure a way to reroute them into the fuse block and ignition so they aren't on a constant hot. The wiring is a mess, I have White used as grounds, red and pink and yellow used as hot wires with those little Tee snap together connectors that cur into the the insulation on the wires, it's a mess and I'm sure more things will go wrong if it's not redone. I wish I had a schematic from the conversion company, but unfortunately I think they're out of business now, they were called (Lorain Motor Coach Co.) out of Ohio, I couldn't find anything on them when doing an internet search. Again...Thank you guys for all your help.