Tailgate lift motor 1988 Bronco

[BBSteal]

Motor for the tailgate gave classic signs the nylon bushings in the motor went. Motor whines nothing happens. So I removed the motor took it apart and low and behold inside full of plastic. I have a spare motor in garage take it apart swap out the new nylon gear, nylon bushings and steel gear to the cleaned original motor. Bench test motor with a battery and gear turns. Take motor to Bronco hook up wires to test it before bolting it in and motor doesn't turn. Check safety rod and latches everything is as it should be but motor wont turn, hook up donor motor and it doesn't turn either . Bench test original motor again on the battery and it turns so does donor motor. So now I hook up multimeter to window motor wires push button on inner tailgate switch and get 11.87 volts push the other post on switch and get - 11.86 volts. I then open the tailgate latches hit the buttons on the switch and nothing on the multimeter so this tells me the safety switch is working. The motor should work but it doesn't what the heck is going on am I missing something or just cursed. Thanks in advance Dan

 

[miesk5]

Yo Dan,
Sorry, I have to roll, so here is some info for you;
Troubleshooting Synopsis; "...The tail gate circuit is pretty easy to resolve with a meter. Attached is a diagram of the circuit. Note that there are two fuses which you may have already found out. One powers the dash switch which is powered only when the key is in RUN or ACC. The other powers the tail gate switch and that line is hot at all times. If the motor is definitely good, (which can be verified by using a set of jumper leads directly to the motor connector). Once it is verified that the motor works then the common problems are: 1. The Latch Safety switch in the left side latch, This is often a problem when the tail gate fails from both switches.(you can pull the connector and jumper it out, which many people leave permanently jumpers out). The problem can be as easy as the latch needs adjustment. So if the jumper makes it work then either leave it jumped, adjust the latching stud for a tighter fit, or replace the latch switch if testing indicates it is bad. The function of the switch is to make sure the tail gate is latched before putting the window up. I like it bypassed because it makes it easy to get the window out of the way when working inside the tail gate. I think I'm smart enough to put the window back down before closing the tail gate . The only suggestion if leaving it jumped is to support the window if it is in the up position with the tail gate down. Else it could be broken by someone leaning on it. 2. The ground return for the tail gate switch uses the same two lines the dash switch does, (the grounding point is under the dash. The dash switch changes the function of the two leads running to the tail gate window motor by grounding one and putting 12V on the other. The tail gate switch uses the two leads for the ground connection, (it requires the dash switch to be in the neutral position in order to work). Depending on the year of the truck there are 2 or 3 connectors involved that often get corroded, sometimes to the point that the wires break off the connector. In your truck, there is on connector behind the left tail light, the next common failing connector is the one on the left side of the rear frame crossover member, (it is gray, if you can still see the color, and just under and behind the bumper). So to make it short, if you can operate the motor with a set of jumper leads and the window goes up and down that way, then the problem is a connection or the Latch Safety Switch. If you can't get the tail gate open to work on it, crawl in the back and remove the tail gate panel and find the motor leads attached along the bottom edge of the opening. Disconnect them and use a long set of leads or another battery in the back with you to test the motor. Once the window is down you can open the gate to make it more comfortable to work on the problem. In the diagram you will see a black with white striped wire that goes to the tail gate key switch, you should have 12V there at all times. To get at it, you will need the window in the up position. The other two leads, (with the dash switch in the center position) should indicate that they are grounded when doing a continuity check of them). You can also check the entire path from dash switch to the tail gate key switch by using a meter and probing the wires the purple with light green stripe and the dark green with light green stripe. Have someone (with the key in RUN or ACC) moving the Dash switch from UP to Down while you check those leads for 12V. If you don't get 12V then the problem is in a connector between the two switches or a broken wire (a broken wire would most likely be where they transition between the body and tail gate due to constant flexing). The procedure would be; 12V missing on one of the wires, move back to the connector behind the tail light (missing there), move to the connector on the cross member (missing there) move back to the connectors in front, until you find where you have 12V on the line you are probing. Once you find 12V the problem is between the last point probed and where you find 12V..."
Source: by Seabronc (Rosie, Fred W) at Ford Bronco Zone Forums

 

[BBSteal]

Miesk5
Thanks for the reply but Im not sure if I explained my problem clear enough. So I'll try to clear it up. I removed my tailgate motor because it was humming but not moving the glass, after I replaced the internals I bench tested it on a battery and it works. At this point I test the tailgate wires with a multimeter and with the gate closed I get a reading of 11.87 volts when the down button on the internal tailgate switch is pushed and -11.86 when the opposite switch is pushed. To test if the safety switch is working I open the gate and push the same tailgate internal buttons and get 0 voltage on the multimeter this tells me the safety switch is functioning. I now install the window motor and get nothing, take it back out test it straight on a battery it works fine test the wires again, 11.85 and -11.85 on multimeter I hook the motor up to the wires and nothing. Im not sure what is going on do I need a traight 12 volts before the motor will turn and if so what happened from the time I took the motor out rebuilt the put it back in. Im at a lose some help please.

 

[miesk5]

Yo,
Inspect connector for corrosion, connector terminal back-out, etc.

With motor installed, glass down, try pushing ******* tailgate, driver side about 6 inches below horizontal glass weatherstrip

 

[BBSteal]

Miesk5
All connections are good. I am getting 11.87 volts to the motor plug when switch is activated, the motor works when hooked to a battery outside vehicle but when installed in the bronco set on the floor it doesnt work. If i hook up the multimeter Im getting voltage if i open tailgate no voltage this tells me the system is working as it should. The motor doesnt work only when in Bronco its very strange.

 

[Tiha]

Miesk5 has it covered like always, but let me try to simplify for my own sake.

The switch or "button" you are pushing to operate it. Is it the one with the key switch in the center?

Or is it the safety operated by the driver's side latch when it is closed?

But I digress,

The motor is reversing DC. To put it simply, as you have probably noticed, Power on one wire runs the motor in one direction, power on the other wire runs it in the opposite direction.

So you have power, but what about ground?
Do you have power on both motor leads while the button is pushed? If so you have a ground issue.

Either way my guess is the switch around the key tumbler in the tailgate. Or connection hither too.

 

[BBSteal]

Okay now im really confused Im going to try & explain this situation more clearly. 1:00 window motor works can hear it run but window doesnt move glass nylon bushings must be broke. I take the motor out take it apart clean out the broken nylon from inside by 1:30, I rebuild the motor with new nylon bushings and gears seal it back up test it on a battery (it spins in either direction when leads are reversed on battery) and put it back in Bronco by 2:30. At this point I close tailgate latch and use the key switch which worked fine at 1:00 to try and operate the window it doesnt move, the motor now doesnt even hum. I cant figure out what could have gone bad (wires ,connectors, fuses) in one and a half hours( sitting in the driveway) the time it took me to remove it rebuild it and reinstall it. I figure Im not getting power so I disconnect the motor and test the leads, with tailgate latch shut I get 11.85 volts when turning key one direction and -11.87 volts in other direction. I am not sure where the motor picks up ground there were no other wires and I did have it installed in the gear after the rebuild so if it picks up ground by contact with the body that should have done it. Also when I first bought the bronco 4 years ago I needed to test the tailgate wiring so to test I just put a spare window motor in the back disconnected the wires in the tailgate hooked up the spare motor with jumpers and it spun when key was turned and dash switch depressed. So I didnt even have the spare motor in the tailgate or touching metal back then and it worked with no extra ground. I assumed the 2 wires in the motor were pos and neg and reversed polarity through the switch. Still need help thanks in advance

 

[miesk5]

Yo BB,
Ground G701 is Behind driver side kick panel
From memory, G701 also serves heater control bulbs, ashtray lamp,

Did you inspect G701?


All '80-96 t/g wiring runs from the dash switch (F2TZ-14529-A Motorcraft SW7071 ~$25~65) out the firewall along the frame to the rear bumper up to the L taillight and into the t/g. '80-86 have a large round 3-wire connector in the LHR taillight well; those with rear defrost also have a 1-wire connector. All years with rear defrost have a ground ring screwed to the body in the taillight well. I think '87-91 have the large round connector in front of the taillight AND a smaller round 4-wire connector inside the frame at the LHR body mount. '92-96 only have the frame connector.

Normal operation is as follows:
RAISE from the dash switch:
Power flows thru fuse 14 thru the LB/BK wire thru the IP switch UP contacts thru the P/LG wire thru the key switch UP contacts thru the Y/R wire to the motor brushes, commutator, & windings; then it grounds thru the motor's internal CB, out thru the R/Y wire thru the latch switch thru the T/Bk wire thru the key switch DOWN contacts thru the Pk/LB wire thru the IP switch DOWN contacts to the Bk wire to the ground in the kick panel (or dash on older Broncos).

LOWER from the dash switch:
Power flows thru fuse 14 thru the LB/BK wire thru the IP switch DOWN contacts thru the Pk/LB wire thru the key switch DOWN contacts thru the T/Bk wire thru the latch switch thru the R/Y wire thru the motor's internal CB to the motor brushes, commutator, & windings; then it grounds out thru the Y/R wire thru the key switch UP contacts thru the P/LG wire thru the IP switch UP contacts to the Bk wire to the ground in the kick panel (or dash on older Broncos).

RAISE from the key switch:
Power flows thru fuse 12 thru the BK/Wh wire thru the key switch thru the UP contacts thru the Y/R wire to the motor brushes, commutator, & windings; then it grounds thru the motor's internal CB out thru the R/Y wire thru the latch switch thru the T/Bk wire thru the key switch DOWN contacts thru the Pk/LB wire thru the IP switch DOWN contacts to the Bk wire to the ground in the kick panel (or dash on older Broncos).

LOWER from the key switch:
Power flows thru fuse 12 thru the BK/Wh wire thru the key switch DOWN contacts thru the T/Bk wire thru the latch switch thru the R/Y wire thru the motor's internal CB to the motor brushes, commutator, & windings; then it grounds out thru the Y/R wire thru the key switch UP contacts thru the P/LG wire thru the IP switch UP contacts to the Bk wire to the ground in the kick panel (or dash on older Broncos).

Note that in ALL cases, EVERY switch is used, and the circuit ALWAYS grounds at the same point.

To eliminate/bypass the dash switch, unplug it & install 2 jumpers as described in the "neutral position" within the diagram. If that text isn't legible, click the pic to supersize it. The following diagram shows how to semipermanently bypass either switch, as well as some other modifications. By Sreve
⊙

 

[BBSteal]

Thanks miesk5 for the reply. Tracking down this problem looks complicated and before I start tearing out switches, wires, connectors, and fuses to check it all. Can you explain to me why I have normal voltage(11.85&-11.87) at the tailgate red and yellow wires when operating the keyed switch or the dash switch. This is perplexing me. Thanks in advance.

 

[Tiha]

You have 11.8x volts on both wires when the key is turned because the voltage on one wire has no place to go, a.k.a. no ground.

Make more sense?

Power goes through the key switch, through the motor, back through the key switch via the other wire all the way up to the dash switch then to ground.

It does not ground through touching the tailgate at all.

Why it failed like it did, Who knows, that is part of an old vehicle.
Electrical connections often fail under the highest loads. Maybe while running the motor and trying to get your window up at 1:00 finally fried the ground point, or even the back of the window switch in the dash.
Loose connections get hot, trying to get the window up, holding the up switch against a locked motor you ran it much longer at higher currents than normal and burnt up the poor or loose connection point in the ground system.
But that is just a theory.
If you check you may very well see a melted plastic on the back of the dash switch.

 

[BBSteal]

Thanks Miesk5 and Tiha for the responses and trying to help me through this. I already thought about having voltage on both wires from your earlier post and thought it didnt seem correct. But I then thought Im getting positive in one direction of the switch throw and negative in the other so with my limited knowledge of a dc reversing motor I thought maybe thats how they work. So I decided to test the idea with my working driver side door window. I disconnected the wire connection at the motor and probed it with the multimeter, when I push the up button I get a reading of 11.46 volts and when I push the down button I get a reading of -11.47 volts so Im getting the same type reading as the tailgate both a pos and neg volt reading. Im a 57 year old gearhead who has had many old cars( 1969 Mustang Fastback, 1970 ford LTD XL convertible, 1979 Jeep CJ-5 and now have the Bronco and a 1985 Mercury Capri 5.0 ) so I understand things break with these gems and enjoy working on them. I won't mind tearing into the wiring even though its not my favorite thing to do on cars but I dont want to start if its not necessary. So my question is if a wire, connector, ground or the dash switch failed what would my reading on the multimeter be at the tailgate wires, I would think I would get a o voltage reading just like when the tailgate latch is opened and the safety switch is working and not any voltage reading as I am now getting, thats what has me confused . Thanks Dan

 

[Tiha]

Let's approach this a different way.

If the motor was unbolted from the lift mechanism will it run with the switch?

I know you said you hooked it to a battery but did we ever verify the mechanism isn't bound up?

 

[BBSteal]

Tiha the motor failed in the classic Ford way internal nylon bushings ground up so I cleaned it out rebuilt it with new pieces, bench tested it on a battery 1 wire on pos 1 on neg turns one way reverse wires turns the other way motor not bound. Hook it to the tailgate wires doesnt move with either switch, check with meter getting reading so I hook spare motor to wires doesnt move either but both motors work when hooked to driver side door switch.

 

[Tiha]

Ok, I was asking if you were bolting the motor to the window lift but it sounds like no you are not.

A digital Volt meter can be your friend but also your foe. You can read voltages on both sides of the motor because the current draw of the Volt meter is so low. Not normal for a volt meter. But a test light may be better.

Either way if it was in my garage I would have to start someplace. You verified the motor. You verified getting power. Now we have to pin it out at each location.

Either at the plug C418 back by the fuel filler neck or the dash switch. I pretty much always start at the dash switch because it basically controls everything.

On the dash switch you are checking pins 2 and 5 for resistance to ground. should be 0 or very close to it.
Pin one should be battery voltage.

Those 3 are easy to eliminate.

Now pins 3 and 4. These are the same as the red and yellow wires on the motor. Holding the button in the up or down position compare the voltage readings on these pins compared to what you see on the tailgate motor directly.
If they are the same you probably have an issue right there inside the switch.
If they are different then you probably have a connection issue between the switch and the rear motor.

So then move to the C418 connection and measure again.
Should be battery voltage and then pressing the button there should be the same voltages you measure on the motor leads.

Same situation. If the reading match the dash switch, your problem is between that plug and the tailgate motor.
If you readings match your motor then your problem is between the plug and forward to the dash switch.

Yes it sucks.

 

[BBSteal]

Success I figured out what was wrong with the tailgate window wiring. I went against advice to start my diagnosis with the dash switch and I started my testing at the tailgate. I decided to disconnect the motor wiring at the connector inside the tailgate that sits above the window regulator gears. After disconnecting I hooked my multimeter to this connector and got the same reading as I was getting before so I wasnt very hopeful, but decided to hook the motor to this connector anyways pushed the buttons and it worked yeah. I discovered the culprit where the wiring failed is a black L shaped plastic piece that the wires are molded into. It is half way between the connector and the window motor in the run and it holds the wires at the bottom of the tailgate via a molded in wire loom body clip. I think the wires running inside must have been damaged but not completely broke so the connection was good enough to pass voltage with no load but couldnt pass enough amps to turn the motor with its load. I used new wiring measured against this run of wires, I then cut the old wires of each end and I ran my new wires along the L and zipped tied and heat shrinked the wires to it, by doing this I was still able to mount the wires at the bottom of the tailgate as it was stock. After swapping over the male connector end I fished the wires under the regulator mechanism and used wire connectors to connect to the motor for future repairs if necessary. After hooking up the motor I greased up the gears and Fluid Filmed the inside of the tailgate and buttoned it up, one problem solved I feel good. Thanks for the replies and suggestions on how to solve this problem, having the pictures and wiring diagrams will be helpful if needed down the road, but I hope I never will need them

 

[Tiha]

That is awesome. Glad you followed your instinct. Common sense says the problem is where you were last. LOL usually anyway.
But then people genuinely trying to help have to start with the basics. If someone had called me to come look at it I would have started in the dash because people don't normally put the effort in that you did before you came here.

 

[BBSteal]

Yea it was definitely a strange scenario. I just couldn't (or refused to) believe my luck was so bad that the dash switch would go bad at the same time I removed the window motor after it had just worked, but who knows there is probably someone out there that has had that happen. I still have trouble understanding the multimeter readings but oh well all is good now. The positive is it did get me inside the tailgate, so latches are adjusted and gears are all lubed and more important my amazingly rust free tailgate is well protected against corrosion. Thanks again to you and Miesk5 for the replies.