1994 F150 won't switch into 4WD
 

I bought this truck 5 months ago, and the truck was glitchy about switching into 4wd from 2wd. it would take three or 4 times of pushing the button before it would make the switch.

recently, it stopped switching into 4wd all together.

I have...
replaced the switch on the dash with a used unit
all fuses appear to be ok, no fuses are blown
replaced the transfer case switch motor with a brand new unit
checked the kick panel 4wd module - it flashes 4 times
I then replaced the kick panel module with a used unit
I replaced 2 relays under the hood that I thought were connected to the 4 wd system, but I'm not sure.

I pulled the transfer case motor off the transfer case and pressed the switch with a helper, and it is not turning/moving, so I think the problem is not in the transfer case.

I'm not sure what else to check? trace wires? check grounds?

Stop swapping parts. Click this, read the WHOLE caption, follow the links in the caption, until you understand how it all works; and THEN start testing things:

https://www.supermotors.net/getfile/...operationx.jpg
(phone app link)

Don't replace anything, until it fails a published test. When you install a replacement, make sure it passes the same test the previous part failed.

thank you Steve83. I am not the best at reading diagrams and running tests as per directions, but I'm giving it a try.

here is what I could find,
The ground wires seem ok, one of the grounds (to the frame?) had 22 ohms of resistance when I measured it against the body, but I think that's why there are two wires, one to the frame, one to the body.
The speed sensor wires checked out ok with 273 ohms - which is in the range.
The sensors check out ok on the transfer case motor. B4 closed, B5 open, B6 closed, B7 open.

I am confused by my readings on the Orange and Yellow wires that deliver power to move the Transfer case motor.
The Orange/A4 and Yellow/A5 both read 12V leaving the Electronic Shift Control Module, But at the Transfer Case Motor, they measure Orange=0V, and Yellow =4.97V, and the black wire has 5 V

this seems wrong to me, but I can't tell from the diagram what's supposed to be happening.

Is the motor supposed to get 12V at the Yellow and Orange wire and the ground is controlled to engage the motor in either direction?
If so, then I guess I have a problem in the wiring bundle between the Electronic Shift Control Module and the Transfer Case Motor/Assembly.

quoted from the instructions:
"Check Transfer Case Motor
To check if the transfer case motor is actually functioning (because it may be hard to hear it in a noisy shop) attach a voltmeter to A4 and A5. Have someone activate a shift and look for a brief (one second) increase in voltage and listen for the relay to click on, then off.
If there is power present, then the control module is trying to run the motor. At this point, unbolt the motor and have someone activate a shift again. If the motor doesn't actually turn, it is malfunctioning and must be replaced.
If there is no power to the motor, check both the power circuits again and the sensors. If there is incorrect sensor data, the module won't power the motor. "
I cannot make sense of this instruction. If I disconnect the wiring harness at the transfer case motor, the control module will not click. and there is no change in voltage at the harness when the switch is pressed. If I plug in the harness at the transfer case motor, the module clicks when the button is pushed, but I cannot attach the volt meter to measure the voltage at the motor.

How am I getting this wrong?

No. More wire doesn't change the resistance substantially. Any reading >5 Ohms from one point on a wire to any other point is a FAIL (open circuit/high resistance).To me, too.Did you follow the link in that caption to this diagram?

https://www.supermotors.net/getfile/.../tcase93es.jpg
(phone app link)

The module reverses polarity on the Y & O wires (they're separate; not a single Y/O wire) to reverse the motor.That's very possible, because that harness runs along the floor. Does the truck have any accessories bolted through the rockers (door thresholds)? Is the floor muddy or wet near the doors? Lift the passenger threshold & carpet, and examine the harness. Do you store heavy, sharp objects behind the seat that might have cut the harness?

http://www.supermotors.net/getfile/8...larpadding.jpg
(phone app link)

BTW
You should read this caption & fill in your signature:

http://www.supermotors.net/getfile/7...oorsticker.jpg
(phone app link)The instructions don't say to disconnect anything for that test. You can use pierce probes as shown & linked in this caption:

http://www.supermotors.net/getfile/1...rs22172dmm.jpg
(phone app link)

...or you can backprobe a connector to "attach" your meter.