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In reading old posts, Serhill posted a diagram and it looks like there should be a ground wire in the plug. My front plug has only the the red, tan and brown wires and my assumption was that the ground was the dashboard it’s screwed to because there is no spade connector in the plug for a fourth wire. The wiring diagram in the TSM offers no detail of this.

If youse is talking about the stock wiring, the front switch connector should have a black wire going to ground. Red is hot, brown and tan go to the rear switch.

When the front switch is in the center position both the tan and brown wires are grounded through the switch.

Both the brown and tan pass straight through the rear switch in its center position.

When you actuate the front, the tan or brown wire is unmade with the black and made with the red. The other stays grounded.

When you actuate the rear switch brown is made with the red and tan stays made with tan to complete the path to ground through the front switch and vice-versa.

My tailgate switch plug on the dash has a 5 pin connector. Tan, 2 reds and brown in one row with a blank and black in the other row. Black is about 4" to the eyelet that's screwed to the dash and another black continues from the eyelet into the harness.

I wonder if someone used a rear plug and switch in the front or some other hackery.

Hope this helps.

Nuts, it just occurred to me that there was an earlier version that used a three wire motor. I don't know when they changed or how the earlier version was wired. Mines an '84 with a two wire motor, brown and tan.

I'll poke around on oljeep.com and see if I can figger out what you've got.

I've found this thread - tailgate window motor ground and looking at wiring diagram from 3rd post, it looks like in 70s there was a different motor/switch design from the most common ("later" years).

What SJTD described above is how later years (with a rocker type dash switch) are wired - there is ground wire to the dash switch and connector is 5 contacts. 2 wires going to the tailgate motor and motor is not grounded through extra wire or body.

Based on the info from thread I linked above, for earlier years (with a lever-like switch) there is no ground at the switch itself, instead the motor is grounded (hard to tell from picture, but probably through body). So the switch is just supplying 12 volt to one of the windings and leaving the other disconnected.

Didn't know about this setup before, I only knew about "later" years and very early Kaiser-era 4-wire tailgate motor (2 windings, ground and armature). Looks like there are actually 3 styles

After some thinking about this setup I got a follow up question - are you putting relays in the tailgate?

If you have that system with tailgate motor grounding through body and "not grounding" switch with relays like I was selling, it can negatively affect movement speed. Since I was not aware of this setup, my relays follow the "later" year one (with grounding at the switch), so they connect one wire to 12 volt and ground the other one.



I think in this case having one winding energized and the other grounded will make the energized winding work harder compared to having other not grounded. If that's the case, you can either cut two wires on the relay module or swap the relays inside the module from SPDT to SPST ones

I have the lever type of switch and a 2 wire motor. I did get your relay kit and it's made no difference but for the life of me cannot figure out why. (While it was apart I discovered the regulator was shot too) I ran a dedicated wire to the relays directly off the battery with a circuit breaker. Still not better, for fun I ran a ground wire directly to the battery with a long jumper to see what would happen. No change. The motor runs totally fine off the battery, great speed in both directions. Everything I read says the front switch ground essential and I have that 4th spade lug on the switch and no connection in the plug. The switch itself is well mounted to the dash and will ground a test light. Was just wondering if there's supposed to be a ground wire in that hole.

When you say that motor runs off the battery, does it mean that it runs slower/weaker with relays?

Another thing that you can do to test theory about ground above - if you put 12 volt from battery on one of the motor wires and leave the other one disconnected, does it run? If it does, how the speed is compared to running it with relays?

If my assumption about grounding through motor body is correct, it should run and it probably will run faster than with relays. If we can confirm that’s the case, I think using SPST relay should improve things

I have a motorcycle battery on my bench I keep charged up. Putting the wires to that battery runs the motor nicely in both directions, so well I was surprised. In the car it barely moves and I have to help it go up because I feel bad for the motor struggling so hard but the relay never trips.
Currently the motor is only grounded through the mount, the relay is grounded well and to the frame. All my battery grounds are new and resistance in the system is very slight. I thought about running a ground wire from the mount to the relay ground but I'm thinking why is that necessary if no one else has to do it that way. Something's not right in my system.
BTW-the motor behaves the same whether I run it from the tailgate key switch or the dash switch.
I was really hoping the consensus would be the ground wire was missing from the plug and my problems would be over. LOL

Triumph215 wrote: ↑Fri Apr 09, 2021 9:49 pm I have a motorcycle battery on my bench I keep charged up. Putting the wires to that battery runs the motor nicely in both directions, so well I was surprised. In the car it barely moves and I have to help it go up because I feel bad for the motor struggling so hard but the relay never trips.
Currently the motor is only grounded through the mount, the relay is grounded well and to the frame. All my battery grounds are new and resistance in the system is very slight. I thought about running a ground wire from the mount to the relay ground but I'm thinking why is that necessary if no one else has to do it that way. Something's not right in my system.
BTW-the motor behaves the same whether I run it from the tailgate key switch or the dash switch.
I was really hoping the consensus would be the ground wire was missing from the plug and my problems would be over. LOL

I have a cigarette lighter connected to the tailgate motor... and an inverter switch... Yes, there is a hole in the tailgate... Never tried to address the why and other causes, Yes I have new glides and window support. An FSJ owner had a simpler way: had a motorcycle battery attached/fixed with bungees to the rear wheel well and the wires were manually applied to the battery terminal.

Triumph215 wrote: ↑Fri Apr 09, 2021 9:49 pm I have a motorcycle battery on my bench I keep charged up. Putting the wires to that battery runs the motor nicely in both directions, so well I was surprised. In the car it barely moves and I have to help it go up because I feel bad for the motor struggling so hard but the relay never trips.
Currently the motor is only grounded through the mount, the relay is grounded well and to the frame. All my battery grounds are new and resistance in the system is very slight. I thought about running a ground wire from the mount to the relay ground but I'm thinking why is that necessary if no one else has to do it that way. Something's not right in my system.
BTW-the motor behaves the same whether I run it from the tailgate key switch or the dash switch.
I was really hoping the consensus would be the ground wire was missing from the plug and my problems would be over. LOL

Looks like extra grounding from relay is the problem. You can try one of three options (listed in order from the most reversible to not reversible):

1. Replace SPDT (5 pin) relays that are in the module with SPST (4 pin). You'll need 2 micro ISO 280 relays, like these from Amazon (that listing is for 3 relays)
2. Cut pin 87a from SPDT relays (effectively turning them into SPST) that you already have like this
3. Cut 2 black wires that go to pins corresponding to 87a pins on relay (not recommended)

I can cut the 87a post off and being I have no intuition about wiring I have to ask...doing that can't make it worse right?
Great story about carrying around a dedicated battery just to run the back window, too funny and kind of sad at the same time.
I'm learning that old Jeeps are interesting animals.

Triumph215 wrote: ↑Sat Apr 10, 2021 5:00 pm I can cut the 87a post off and being I have no intuition about wiring I have to ask...doing that can't make it worse right?

If you've confirmed that your motor is grounded through body (runs with 12 volt to only 1 wire while other is floating (not connected to anything)), you should be fine.

Removing 87a pin will make the relay module mimic switch behavior - it would put 12 volt on one lead and leave the other floating instead of grounding it.

Excellent and thank you, I'll make that modification tomorrow and report back.

LOL I was so excited to go cut that post off this morning that I forgot my truck is at the shop having the rear main seal replaced. I'll make the mod as soon as I have it back home.

Well I had to leave town for three weeks right when I got the truck back and am just now getting around to trying this relay fix. I'm happy to report that it worked exactly as you described. I cut that post off and the window goes up and down at the proper speed.
Thanks very much for all the help as I wrestled with this issue.
Now I finally feel I have a real and functioning vehicle.
It runs well now, no oil leaks anymore and I can use the cargo area. Woo Hoo !!

...and now the dash switch doesn't work.
Not super upset because at least the tailgate switch works now but boy, it's always something.

My bad, operator error.
The dash switch works perfectly, I just didn’t have the truck running.