Rear Windshield wiper
 

The motor is new, voltage gets to the plug (12V), but the wiper still doesn't work. I'm completely at a lost as to what the issue is. Thoughts?

wrong polarity? not enough amps? stuck?

Just curious as to how you checked the voltage at the rear wiper motor's plug, because the '89 FSM (ref. page S-40) omits a very important step that would make it impossible to measure ANY voltage at the motor plug -- you need to do this test with the hatch FULLY CLOSED to complete the wiring circuit that is made by the contacts on the hatch strut. If you're measuring voltage at the motor's plug, which is revealed only after you remove the plastic trim piece covering the motor then you obviously figured this out for yourself.

The schematic diagram shown on page S-39 of the '89 FSM shows a normally open, single pole, single throw switch, wired between one leg of the motor and ground. This leg of the motor also connects to the intermittent wiper relay in the cluster switch. Appears that switch is a limit switch, probably built in to the motor and there to reverse the motor's polarity each time it reaches the end of its travel.

Did you try the "Checking Wiper Motor" test on the bottom of page S-40? This test has you jumper +12V to the LG/Y terminal of the motor, and jumper the B/R terminal wire to ground, motor is supposed to turn. If that fails, FSM refers you to page T-25 to test the rear wiper & washer switch.

I thought there might be something wrong with the amps... but that just doesn't make sense as all of that is still stock. I doubt it's stuck either as the motor itself is straight from the dealership.
Yup.
I'll have to check that out. Is that the Body electrical book?

Yup, that's the body electrical section. I've got the '89 FSM, big orange binder type FSM, which is one of the few editions where they didn't have a separate book for the schematics & wiring diagrams. Sections S and T in my edition. BTW, the color codes given in the FSM didn't even match the ones in my '89T2, nor did the shape of the plug shown, but it's easy enough to figure out - if the motor doesn't run, just reverse polarity.

My rear wiper doesn't work either, but it's because it's not getting a full 12VDC at the motor terminals - it's a worn out wiper switch relay in my case. I used one of those matching T-style connectors I've kept from my old engine harness to substitute for the wiper motor connector, so that I could connect that to my DVM and see what voltage the motor would see with the hatch closed at the end of the circuit line. Was getting only about 2VDC with the wiper switch on the LOW setting, and about 10VDC at HIGH. Motor would barely budge at all in the LOW setting, worked VERY slowly at HIGH. This problem started for me after I accidently flipped on the rear wiper when it was iced to the glass one snowy day - probably hastened the burning or relay contacts. Fortunately all my front wiper functions are fine, but I need to replace/refurb that wiper switch one of these days.

Cool. Yeah, I just double checked the body electrical on the 86-87 FSM, but they don't have anything regarding the rear wiper. I'll have to ensure I'm getting those voltages when it's fully closed and functioning. I'm surprised one would have to reverse polarity on a DC motor though to get it to function. The motor should work regardless of polarity--it would just run one direction instead of the other unless there's a diode in there somewhere... I shouldn't have chucked my old wiper motor.

Check your switch... I had the same issue. IIRC, the motor always has voltage but doesn't run until the switch grounds to complete the circuit. I fixed mine probably three years ago so don't quote me.

http://nopistons.com/fsm/88FSM/15_BO...CAL_SYSTEM.pdf
Page 15-17 to check the switch.