Help! Rebuilt Headlight Motors, right one still INOP

[vinman60]

Hi Folks, Just rebuilt both headlight gears on my '90. Driver's side worked perfectly. When I put passenger side in, driver would only open 1/2 way and stopped, passenger not at all. Passenger Motor was hot as well. When I unplug motor on passenger, driver side works perfectly. Been reading all afternoon, 90's don't apparently have relays, have a control module. Tested for voltage with a Multimeter, driver looks like it gets a quick pulse going from positive to negative when you go from on to off. As it's a digital meter, meter may not be fast enough to accurately read pulse, so I assume the motor load must complete the circuit. I get no pulse on the inoperative side. I'm also making an assumption that the control module must monitor load of both sides. Leaning to a bad motor coil, it travels perfectly with the manual k'nob. But without seeing any voltage, I am worried that there is another open component in the circuit too.

Thanks!

 

[vinman60]

Believe It to be ACM

On other threads, found a schematic that shows the headlight circuit to a 1993. Other than the off wire being white on a 1990 versus a green on the diagram, the terminals were the same. Thought I may have had a blown fuse on the RH Motor, but after exhaustive searching for the fuses, I read the OM in the car and it indicates that there is a circuit breaker on the light switch for the lamps. Anyways, had +12V on the reds which are LH and RH Motor power and +12V on the White when the switch for headlamps are off. This goes to zero when switch is on and yellow goes to +12V signaling the ACM to turn the headlights on. Found a really great write up on how the ACM works too. Basically, to eliminate relays for up and down, the ACM detects current draw. When the motor goes to full up or down and hits the stop limits, the motor draws more current as it is driving into more load. The ACM senses this and shuts off the circuit. It is independent for each side. In addition, apparently there is a time limit cut-out in the module as well. This is in case the gears are stripped and the motor would run forever due to lack of load. I believe it is 5 to 6 seconds.

The part number for the ACM is a GM Headlight Actuator Control Module #16521297. I will let you know how I make out, but others seem to have had positive results after either buying new motors. Last note, the plugs for the motors are keyed. I believe the heat was simply a reverse polarity, so take care when plugging them in, pretty dark down there. One pin is keyed at 12 O'clock, the other at 3, but you can force past these small keys if you are not careful.

 

[Schrade]

FULL headlight diags here:
Headlight clicking and half-turns - repair with pics... - Corvette Forum : DigitalCorvettes.com Corvette Forums

I have the snappics to go with each step which I deleted from the original CF Sticky, after gettin' banned

 

[vinman60]

Thanks Shrade

Only thing I didn't do was to try 12V directly to motor and reversing polarity to see if motor actuates. Left one works perfectly when I unplug the right one at the 2 - wire motor connector at the end of the harness. I'll give that a shot as well to see if motor operates. Did you use fused jumpers? Diagram says 30 Amp for power, likely has a fairly high inrush current when it first turns.

 

[Schrade]

Alright vin - just re-read your OP; when P side motor got hot, you might have cooked something. If I was you, I would disconnect both headlight motors until you find the EXACT problem. You could be lookin' at a fire hazard here, or a battery drain at best...

I'm readin' my notes on the FSM schematic from the other post, and I didn't use a fused jumper. I DID note that if you do so, it's at your own risk...

Since your D side works with the P side motor unplugged, try the reverse then, just to see if it will cycle under ANY condition.

Post results...

 

[vinman60]

Alright vin - just re-read your OP; when P side motor got hot, you might have cooked something. If I was you, I would disconnect both headlight motors until you find the EXACT problem. You could be lookin' at a fire hazard here, or a battery drain at best...

I'm readin' my notes on the FSM schematic from the other post, and I didn't use a fused jumper. I DID note that if you do so, it's at your own risk...

Since your D side works with the P side motor unplugged, try the reverse then, just to see if it will cycle under ANY condition.

Post results...

No risk, no reward.... I left both sides disconnected. I did try reversing them, no result on P side. Making up a test lead now and using a jumper pack to test. I'll let you know if the motor works. I am suspicious of this motor, as it disassembled differently than the D side. 1/4" bolts were on the inside of the housing. I know they are reversed, but this one also looks smaller than the D side, may have been replaced before. Good news is I now have lights that stay up when cranked manually so I can get a sticker. PO didn't mention that issue, but being an electronics tech, not concerned I won't find the issue. I try to replace the right part the first time, this one had multiple issues, P side apparently hadn't worked for about 5 years according to PO.

Thanks Man!

 

[vinman60]

Passenger Side Motor is junk

No risk, no reward.... I left both sides disconnected. I did try reversing them, no result on P side. Making up a test lead now and using a jumper pack to test. I'll let you know if the motor works. I am suspicious of this motor, as it disassembled differently than the D side. 1/4" bolts were on the inside of the housing. I know they are reversed, but this one also looks smaller than the D side, may have been replaced before. Good news is I now have lights that stay up when cranked manually so I can get a sticker. PO didn't mention that issue, but being an electronics tech, not concerned I won't find the issue. I try to replace the right part the first time, this one had multiple issues, P side apparently hadn't worked for about 5 years according to PO.

Thanks Man!

Made up test rig, D side works, P side INOP.