I've had a few requests to see what I did when I fixed/rewired the tailgate in the silver Wag. I'm finally posting some stuff!
Backstory: Wag is my dad's that I have on extended loan with the condition that I fix what it needs while I have it. One thing that didn't work when i got it was the tailgate window. When I got to opening it up I found multiple problems. The main problem was the window channel was rusted into what started as two pieces. Got a new one from BJ's and installed it.
Next problem was that the motor wouldn't move from either the key switch or dash switch (safety switch bypassed). When given voltage directly (from a spare battery I had nearby) the motor worked. Could never get the key switch to work, so I decided to forget about that-this tailgate was only going to move via the dash switch.
The three heavy gauge wires in the tailgate all tested good: the +12V hot wire and the two wires which were alternately +12V/ground depending on when the motor was going up or down.
I cut the two motor wires and used them to trigger SPDT relays and tapped the third heavy wire for voltage. I used a third relay to make a single, dedicated 10 ga. ground wire that runs straight to the negative battery terminal. The ideal setup would be a NEW 10 ga. hot wire also direct from the battery (with 30A fuse).
By not having to rely on old, rusty, chassis ground for serious work the tailgate window goes up and down quite briskly now!
For background info on how SPDT relays work, I highly suggest http://www.the12volt.com. There are a lot of cool projects on there using these simple relays.
Diagram:
Picture of relays installed inside the tailgate:
If you want to buy these and don't have any luck at Radio Shack the relays and socket plugs for them are available from http://www.digikey.com.
Also, the terminals are the same on all SPDT relays. In MOST cases, it doesn't matter which low-current side (85 and 86) is voltage or ground. As long as current goes through 85 and 86 it will actuate the high-current switching (87/87a/30). There are a few special cases involving diodes, IIRC. Again, check out http://www.the12volt.com for more info on relays. To clarify, the chassis ground on the top right relay IS NOT connected to terminal 85 on the top left relay.
The third relay is there to make things "neater," IMO. Without it you would need to run 2 ground wires to the battery instead of one OR splice them together (I didn't want to do another splice or worry about ground loops or accidental backflow current). If you need to be cheap and have more wire laying around then fine, you can do it that way, but I had extra relays and prefer to keep things tidy and simple. Each relay cost me about $1, so I thought the extra expense was worth it.
Let me know if you guys have any questions!
they will burn up especially if not fused {Less than 30 amps} in a short.
