Tailgate window motor rewire

[HowardT64]

Thanks!! I am good to go now Letank!!

[dh3rm3]

Hello FSJeepers,

I'm unearthing a old thread here as I spent some time trying to sort my tailgate issues.
As it was not working, I replaced the original dashboard switch with a marine toggle switch connected to two relays as described at the beginning of this thread. (All is made under the dash, I got rid of the original switch harness, and ran 2 new tan and brown wires to the tailgate directly connected to the motor. The safety switch is bypassed. )
It works great. The dashboard switch operate while running, or in accessory position.
Knowing that the tailgate switch is grounded through the dashboard switch, and as I was forced to get rid of it, I wonder if there would be a way to get the tailgate switch to work with this new configuration. The switch is always powered a 12V, so I guess it's not working now as the ground is no longer there.
So hence my little ask for help : Is anyone has an idea how to ground (the motor) for it to work from the tailgate switch in this configuration ?
Thanks in advance.

[jaber]

My first thought would be to find the ground screw for the rear harness, clean well and run a wire into switch.
Keep in mind I'm in Az. and don't have to deal with major rust. If that were the case, a new wire from a trusted ground.

[dh3rm3]

Thanks Jaber.
That's what I was planning. I was hoping it would be possible without removing the tailgate window, but I guess I'll have no choice.
(Impressive list in your sig ! I haven't specified it in my post : my rig is a 79 Cherokee)

[devildog80]

You can do this without removing the glass. It just needs supported when gate is down and glass extended out as if closed.

The original rear window motor ground was off the original dash switch, and attached to ground just above parking brake release. If you have removed the original dash switch, and bypassed the safety switch, where is your now existing switch grounded? This is the only ground you should need for the back glass motor, through the switch. Any other grounds you find inside the tail gate, are for license plate light, and tailgate to rear frame/body.

You can see the empty hole in first pic on the left, looks like a star washer was there, just above park brake release lever.
20230615_191042 by Scott Weckerly, on Flickr

I redid my rear window ground, incorporated in with some others under dash, and direct to the battery through a grounding strip mounted under dash.
20230615_183301 by Scott Weckerly, on Flickr

Ground strip under dash, then tied to ground strip under hood by battery
20221127_142915 by Scott Weckerly, on Flickr
20221127_151328 by Scott Weckerly, on Flickr

[dh3rm3]

@devildog80

I went for the 2 relays option described at the beginning of this thread, that I adapted a little bit.
Tan and brown wire going to the motor are on pin 30 on each relay.
The relay is activated when the new switch (on the picture near the vent activator) connects to ground.
All three pins on the switch are actually connected to ground, one (middle position) directly to ground, and top and down, via pin 85 of the relays.
That's why I don't understand why the rear tailgate switch does not actually work. I thought the ground would be provided by the relay, and also by the switch, and that it would complete the circuit... but hum... does not work...

The detailed configuration goes as follows :
Brown and tan wire on pin 30 of each relay, going straight to motor.
Accessory 12V on pin 86. (taken from the original dash switch)
12V straight from battery and fused on pin 87
Ground to 87a on both relays (which is a closed circuit, so ground should always be there... I guess), straight to battery ground.
Up and down pin of the switch to pin 85 of each relay
And switch middle pin directly to battery ground.





So this works great, when the car is running, or in accessory position. But the tailgate switch does nothing.
As far as the new switch and the relays are grounded, what am I missing there ?

[dh3rm3]

As english is not my native language, a drawing is worth more...
This is the simple schematic for one relay.
Same goes for this other one, with tan wire in place of brown.
Considering that the tailgate switch is always 12V hot, I guess don't need any power going to it in this configuration ?
Or am I wrong ?
So the whole circuit is grounded, just as it was with the original dashboard switch.
The new switch's middle (inactivated) pin is by default grounded (straight to bat).
When up or down, also grounded.
And both relays are grounded through pin 87a (which is closed by default)

[Srdayflyer]

to all the CRIMPS out there, i always use heat shrink over the connectors, and im not talking th c.a.s. ones from home deopt/lowes/harbor , i use the type that has a thermo set glue inside avail ebay/amazon when you use this type you cn absolutely figure 2 things permanent seal, and no moisture penetration's , and i protect the bundled wires with split sleeve wire loom , all not that expensive for the step over a dollar to pick up a penny crowd, i kinda like to only do it once and not have trail issues , IMO

[tgreese]

relay.png

In your diagram, you are switching the ground, with the coil "floating" at 12V all the time. This will work fine to energize the coil. You need to protect the wire at 86 (12V power to the coil) with a fuse or circuit breaker at its origin. The 12V at 87 only powers the motor. With the relay open (switch off), the motor is connected to ground. When the relay is energized (switch on), the motor is energized.

With two relays, I presume one relay supplies ground to the motor and the other supplies power to the motor. You select direction by connecting the two relays in reverse from each other (I presume). If the motor has a connection "A" and "B," connection "A" goes to 87 on one relay and 87a on the other, and "B" goes to 87a and 87 resp.

[tgreese]

to all the CRIMPS out there, i always use heat shrink over the connectors, and im not talking th c.a.s. ones from home deopt/lowes/harbor , i use the type that has a thermo set glue inside avail ebay/amazon when you use this type you cn absolutely figure 2 things permanent seal, and no moisture penetration's , and i protect the bundled wires with split sleeve wire loom , all not that expensive for the step over a dollar to pick up a penny crowd, i kinda like to only do it once and not have trail issues , IMO

Yes, you want adhesive lined heat shrink tubing. Available from the parts houses like Digikey and Mouser (though navigating their sites can be challenging to the uninitiated). Maybe Parts Express instead - https://www.parts-express.com/3M-1-8-He ... quantity=1
I recommend 3M brand - other brands may be ok, but the 3M stuff is known good.

They also sell split loom by the foot - https://www.parts-express.com/search?ke ... vance:desc

[tgreese]

Regarding your original question, as I understand it, motor power is now being switched at the dash by your relays. The relay coils are powered by connecting to ground at the dash using your new toggle switch.

To switch the relays at the dash from the tailgate, you will need to run at least two wires to the dash to provide the same grounding that your new toggle switch provides - one wire for motor going up and one for going down. If you must run two wires to the tailgate, IMO you may as well run a third to provide your ground. I'd bring the ground for the tailgate switch back to the same point in the dash as the ground for your toggle switch.

[dh3rm3]

Hello @tgreese
Thank you for your reply.
And I apologize in advance if I seem completely dumb, but I'm neither a good electrician, neither a fluent english.
But I'm still trying to understand what I'm missing here.

The two relays are exactly connected in the same way, except one has the brown wire going to the motor on pin 87, and the other one, has the tan wire, also on pin 87.
I did no inversion. As this, it works when the wires are connected directly to the motor.
For the two relays, pin 87 is powering the motor. Goes up and down with no issue.
I'm sorry, but I don't understand your relay inversion thing. The motor runs on inversion of power/ground. So when one relay sends power through the tan wire, for instance, brown wire is ground. The second relay, sending power throught the brown wire, tan is the ground. I think I don't need no swapping of connection on pin 87 and 87a.

But I'm stuck in a 2 case scenario : with the wiring as I described :
- tan and brown wires are connected directly to the motor. The tailgate switch is bypassed. So obviously, the tailgate switch does not work, but the switch I installed, connected to the 2 relays, as I described above, works.

- tan and brown wire (still coming from the relays) are going to the tailgate switch, then from the tailgate switch to the motor. In this case, tailgate switch works, which means taht it has a ground, but my new dashboard switch does not work in this configuration.

Obviously what I'd want is both switches to work.
I guess I'm not that far but missing some important thing.

Cherokee is my daily rig. I use it everyday. As I'm lost in the woods away from everything, it's my connection to the world. That's why I'm trying to do things without having to remove the window. But this way, I have obviously absolutely no access to the tailgate switch to see how it is wired.
So I'm going by trial and errors, tailgate close, window up and me in the cargo area.
Depending on how I'm wiring the brown and tn wires (whether directly to motor, or going through the tailgate switch), relays are working, or not.
Everything in my setup, I think, relies on how the tailgate switch is wired. When not activated, and being powered by it's own permanent 12V, does it let current pass through tan or brown wire to go to the motor, or not ?

[dh3rm3]

I hadn't seen your second reply.
Ok I'm starting to get it.
The goal would be to activate the relay from the tailgate switch.
So 2 ground wires from relays pin 85 to brown and tan wire to the tailgate switch.
But where would I connect a third ground wire ? As I have currently no access to the tailgate switch itself.

[tgreese]

Year/model/equipment? We could look at the schematic if we knew the year, and get an idea about the tailgate switch. These Jeeps were built over three decades, and things change.

[dh3rm3]

It's a 1979 Cherokee Chief.
Classic AMC 360 / TH400 / Borg Warner Quadratrac
I looked a bit everywhere, and according to what I found, in 79 the tailgate switch grounding was modified to be grounded by the dashboard switch. Prior to that it was grounded to chassis.

[tgreese]

Before you replied, I looked at the '82 wiring diagram. That does not show any relays. Instead, it sends the power from the dash directly to the motor. The tan and brown wires are 12 ga, which is a large gauge wire. You need this big wire to handle the current of the tailgate motor.

With the relays, your switch in the dash controls the relays, and the relays control the motor. To use the switch in the tailgate, it also will need to control the relays.

You could approach this one of two ways, as I see it. First, you could remove the switch from the tailgate and 'characterize' it. Use your multimeter and test what it does in each position. Then see how you can connect wires to control the relays.

Or, you could print out the wiring diagrams for 1979 and trace out the tailgate circuits. This may tell you enough that you can connect the switch without removing any wires or the switch.

[dh3rm3]

I'll keep on investigating and try to activate the relays from the switch.
As a reference, I found this video : https://www.youtube.com/watch?v=gobhl-9Wu0A
Tailgate switch has 5 wires, and a constant 12V power feed.
I guess that by swapping this feed to a ground, I'll achieve what I want.
Thanks for your involvement.
Once I find out, I'll report my findings back here.

[Srdayflyer]

yes there are only 5 wires that run the rear window excluding the defrost wires the problem with these jeeps is the tailgate area. in the drivers side corner the wiring bundle passes thru 2 slots 1 in the body and a 2nd in the tail gate the whole problem is that over the 40+ years the copper wires work harden and break internally, the 12v power wire is HOT all the time so when working properly you can lower the glass and open the tailgate. the connection for this wire bundle is underneath where the pass thru is. i pulled my harnass from the tail gate and found the 2 crimped repaired wires i could see at the pass thru but i also found the power wire had only 4 strands intact and the insulation hard and cracked i spliced in 2 feet of all new wires in the motor bundle and defrost , and well slap me silly it works like new, i did pull the glass and the regulator to clean and regrease and replace the regulator arm pins that were worn in half ,they ride metal to metal on the window suport they raise and lower the window(real crappy design) new pins are avail. from bj's or team waggy, so IMO all this rely crap is something to do with nothing , with someone wanting to reinvent the wheel from round to square and sell you on the idea its better, these jeeps for the most part are simple rigs to work on jeep didnt change hardly anything in 40+ years, and the earlier the model the simpler it gets, i spent 4+ years going thru every possible wire connection ,body panel dirt /debris collection point, system and sub system cooling,a/c , fuel , brake, drive train, fabricated bumpers, interior/sound proofing on this jeep so do i consider myself an expert on my daughters cherokee HELL YES, i spent 45 years as an aircraft mechanic so i do things right the first time, so if you have any questions about anything feel free to reach out to me , regarding your fsj i have several at length blogs here on cooling and fuel injection i did or had issues with ,

[Srdayflyer]

the contact switch controlling the tailgate window may need replacement oem is hard to come by and BJ'S sells a really nice aircraft grade waterproof switch, or buy all the manual(hand crank) assy stuff from either bj's or team grand waggy and not worry about the electrics.

[tgreese]

Looking over my previous posts, I apologize for maybe not being very helpful. Partly, I did not spend enough time understanding the problem, and part I did not compose my reponse very well.

Before I address the OP's issue more specifically, I want to comment on Srdayflyer's post above.

I expect he is right; the main problem with these tailgates is the wire pass-through from the body to the tailgate. However, using relays likely has some value, regardless of the wire-pass-through problem. Relays are used to take the current load off of switches. Powering a motor, at turn-on there is a large inductive load (current surge) until the magnetic field is established and the motor starts turning. Then at turn off, there is an inductive kick (current surge) as the motor's field collapses and the motor stops. The switch contacts are old and possibly not sufficiently beefy from the factory to handle these normal current surges. Jeep's engineering of these secondary systems was not great.

When you add the relays, you take the load off of the switch contacts and place it instead on the relay contacts. The switch now controls the relay, and the relay now handles the current surges. If switch failure is a problem for these tailgates, adding relays seems like a good idea.

Now to the OP's problems - let's look at the switch in the tailgate.

It is meant to do two things. First, when power comes from the dash control switch to the motor, that power must pass through the switch and go to the motor. Your relays under the dash work because the switch in the tailgate sends the power from the dash to the motor.

Secondly, the switch is meant to activate the motor when you use the key at the tailgate to move the tailgate window up or down. When you turn the key left or right, the switch disconnects the wires from the dash and uses its own power source (power and ground in the tailgate) to run the motor up or down resp.

With the relays under the dash, there are no wires going to or coming from the tailgate that can be sent to the dash and control the motor. All the control of the motor from the tailgate key switch is inside the tailgate. There are no external wires to or from the switch, except for 1) the pass-through wires from your dash switch and 2) power and ground that run the tailgate motor.

Realize that, when you turn the key switch, you are disconnecting the wires from your relays (the tan and brown wires). The drawing at the first post in this thread shows you how to add relays that are in the tailgate. You could put the relays under the dash, but you need to run wires from your added relays to the switch in the tailgate.

Looking at the drawing in the first post of this thread, control comes from the existing motor wires labeled "+12 up" and "+12v down." These now control the relay coils in the two upper relays. I expect the easiest way to see this is with a truth table -

tailgateRelays.png

UP and DOWN are the two upper relays, connected to the motor up and motor down wires resp. AUX is the third lower relay.

Here 12V is the original motor power that now controls the relays. The polarity of the coil connections does nothing (there is no polarity actually), and is irrelevant. GND is connected to the body/chassis ground. Null is floating, ie not connected as a circuit. Plus and minus are the battery connections in the drawing, used to power the motor.

You can see the power coming from the original tailgate motor wires, and how the output switches depending on which relay(s) you energize. Note the DOWN and AUX relay coils are in series - this seems to be ok, though I would have put them in parallel.