1985 Corvette Headlight Motor
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5th Gear
Joined: Oct 2018
Posts: 5
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1985 Corvette Headlight Motor
I have an '85 that I have been having troubles with the driver's side headlight for years.
It won't open, or close. Both headlights light, in both normal and bright.
The motor was new when I started to address this issue, so it's not that.
This is where I am:
It won't open, or close. Both headlights light, in both normal and bright.
The motor was new when I started to address this issue, so it's not that.
This is where I am:
There is 1 red wire that supplies all the power.
It comes into the headlight relay. It also shows 12 volts, so the fusible link is good.
There are 4 wires come out of the relay.Yellow runs across to the other side relay.
Black is ground.
Drk Grn and Wht go to the headlight motor. I found a break in the white, and fixed it.
Keep in mind; the passenger side works, as it should.
I swapped the relay and then both sides stopped working, telling me the driver's side relay is bad.
But also, putting the good relay of the driver's side still didn't fix the problem.
With the good relay in each circuit, the Drk Grn measures 12v when the headlight switch is on.
When it's off, the grey measures 12v - when it's on, 0v.
The wht never has any voltage in either position. This I don't really understand, because the passenger side has the same reading, but works fine.
I'm not sure what the isolation relay does.I had already replaced both headlight door relays and the isolation relay.
Although, it appears the driver's side relay is bad.
Any ideas where to go from here would be greatly appreciated.
Thanks,
Jeff
It comes into the headlight relay. It also shows 12 volts, so the fusible link is good.
There are 4 wires come out of the relay.Yellow runs across to the other side relay.
Black is ground.
Drk Grn and Wht go to the headlight motor. I found a break in the white, and fixed it.
Keep in mind; the passenger side works, as it should.
I swapped the relay and then both sides stopped working, telling me the driver's side relay is bad.
But also, putting the good relay of the driver's side still didn't fix the problem.
With the good relay in each circuit, the Drk Grn measures 12v when the headlight switch is on.
When it's off, the grey measures 12v - when it's on, 0v.
The wht never has any voltage in either position. This I don't really understand, because the passenger side has the same reading, but works fine.
I'm not sure what the isolation relay does.I had already replaced both headlight door relays and the isolation relay.
Although, it appears the driver's side relay is bad.
Any ideas where to go from here would be greatly appreciated.
Thanks,
Jeff
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
You've done a pretty good job of figuring out this complex circuit. I'm assuming from your analysis, that you have the FSM. Is your headlight door motor new, or is it a JY motor? With the door closed, and you have 12 v. on the green wire and no voltage on the white wire, that tells me you have either a bad connector, a bad motor, or a defective or dirty limit switch. I'd suspect the dirty limit switch first. If you're not familiar with the limit switches, here's a link to a video on the '84-'87 headlight motors, although this vid does not specifically address the limit switches:
https://www.corvetteforum.com/forums...placement.html
The white wire is a "switched ground" wire, and should never have voltage.
https://www.corvetteforum.com/forums...placement.html
The white wire is a "switched ground" wire, and should never have voltage.
Drifting
Joined: Mar 2013
Posts: 1,952
Likes: 239
From: Venice Cali.
This is a longshot but I met the guy who use to put the headlight motors together at gm in
Van Nuys plant. He said whenever it gets stuck just turn the **** slightly an the bottom of the motor to move the connection to a new area.
Haven't had a problem since.
Good Luck
Van Nuys plant. He said whenever it gets stuck just turn the **** slightly an the bottom of the motor to move the connection to a new area.
Haven't had a problem since.
Good Luck
Thread Starter
5th Gear
Joined: Oct 2018
Posts: 5
Likes: 0
I appreciate the responses.
I went though everything again today.
Since the passenger side works correctly, I tested all the voltages on that side first.
Results on passenger side:
grn/wht 12v when headlight switch on - 0v with headlight switch off
grey (the schematic states Red, but it's stock, and it's grey) : 12v when headlight switch off - 0v with headlight switch on
wht: 0v always
Results on drivers side:
grn/wht 12v when headlight switch on - 0v with headlight switch off
grey (the schematic states Red, but it's stock, and it's grey) : 12v when headlight switch off - 0v with headlight switch on
wht: 0v always
So, it appears the wiring is OK, although the wht wire driver's side was broken. Also, the driver's side relay is shot.
After all the above, I put the good relay on the draver's side and tried it. The HL door was half open and it closed when I turned off the switch, but then did nothing after that.
I have pulled the motor and will be going through that tomorrow. I know the gears are fine, so I have to see why it's hanging up.
Just a note:
I called Ecklers today to run things by a tech.
Total waste of time.
After telling him the story, including the year, he stated, "Oh, that's a vacuum system."
At that point I figured I knew more about this than the expert.
I went though everything again today.
Since the passenger side works correctly, I tested all the voltages on that side first.
Results on passenger side:
grn/wht 12v when headlight switch on - 0v with headlight switch off
grey (the schematic states Red, but it's stock, and it's grey) : 12v when headlight switch off - 0v with headlight switch on
wht: 0v always
Results on drivers side:
grn/wht 12v when headlight switch on - 0v with headlight switch off
grey (the schematic states Red, but it's stock, and it's grey) : 12v when headlight switch off - 0v with headlight switch on
wht: 0v always
So, it appears the wiring is OK, although the wht wire driver's side was broken. Also, the driver's side relay is shot.
After all the above, I put the good relay on the draver's side and tried it. The HL door was half open and it closed when I turned off the switch, but then did nothing after that.
I have pulled the motor and will be going through that tomorrow. I know the gears are fine, so I have to see why it's hanging up.
Just a note:
I called Ecklers today to run things by a tech.
Total waste of time.
After telling him the story, including the year, he stated, "Oh, that's a vacuum system."
At that point I figured I knew more about this than the expert.
Last edited by JPSalty; Oct 18, 2018 at 12:01 AM.
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Thread Starter
5th Gear
Joined: Oct 2018
Posts: 5
Likes: 0
Roy,
I think what you're talking about is my problem, bit I'm not sure which are the limit swithes.
Riddle me this Batman...
I think what you're talking about is my problem, bit I'm not sure which are the limit swithes.
Riddle me this Batman...
I took the motor apart.The gears were all good.I dabbled around in there for a few minutes.Nothing looked amiss.I put it back together, bench tested it.The motor worked.I put it back on the car.The headlight went up and down a couple times.I went about putting my tools away.I tried it again.Nothing. Doesn't do anything again.
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Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
You said this is a new motor. Since you didn't say, I'll ask again. Is this motor really new, or is it a junk yard motor?
When you bench test the motor, you'll never find the problem, because the limit switches will only work when the headlight door hits its stops, which can't happen during the bench test.
Be sure to use a light weight white grease* on the motor shaft bearings. The motor armature must be able to shift on its axis to actuate the limit switches.
* LubriPlate or CRC Sta-Lube