GT headlight doors

[Sport Fury GT]

My 70 GT was damaged in a parking lot incident. The front clip was removed, damage repaired and repainted with new stripes installed. A test drive revealed the headlight doors wouldn't operate. And I could hear what sounded like a relay clicking every few seconds. I returned the car to the shop for that reason and a couple other minor electrical issues. After a week, they still cannot get the headlight doors to operate consistently. Any ideas on what the issue is and how to solve it?

 

[Pete Kaczmarski]

Try to tap moderately on the headlight motor when the switch is on. As the motor is verticle, the armature has slight corrosion near the motor endcap.

 

[Davea Lux]

The clicking is probably from the circuit breaker in the light switch. Could be a stuck motor, there is a knob on the bottom of the motor, try turning that to see if the motor will turn. If not, you may have to have the motor disassembled and rebuilt. Caution, the end cap on these motors has a small circuit board that holds the brushes an that will get broken if the motor is not disassembled correctly. (circuit board is not available) Your motor may have been damaged when the car got hit or there also could be binding in the headlight doors. I would turn the knob on the bottom thru a full cycle of the headlight doors to see if it turns freely. That will eliminate a bind as the source of the problem.

Dave

 

[Davea Lux]

The other thing that you would want to check is to see if the motor is properly clocked. Remove the two clips that hold the drive shaft into the headlight doors. Turn on the headlights with the key on and see of the drive shaft moves to open the doors. It is possible to install the drive shaft 180 degrees off so the the linkage will be locked up when the headlights are turned on.

Dave

 

[Big_John]

There's some basic diagnostics that need to happen BEFORE you can determine what the issue is.

1. Disconnect the plug at the headlight motor. With a wire running from the positive lead on your battery, touch one side or the other of the plug to the motor. DO NOT GROUND THE OTHER CONNECTION. Try one and if nothing happens, try the other. If it opens, switch the wire to the other connector and see if it closes. Do this in the car with everything hooked up. The motor can get screwed up if tested out of the car and although it's been done (including by myself) with no damage, let's not tempt fate.

If the motor works, it's time to try the power.

2. Connect a test light (or multimeter) to one of the terminals at the plug (from the wiring harness) and with the ignition switch in the RUN position (important), turn the light switch ON. If no light, switch to the other terminal. You should have power at one of these terminals. Now switch the connections and turn the light switch OFF. You should have power at that connector.

No power could mean a few things. The relay under the dash sounds like it's making noise, so that means the light switch is functioning. It also means the relay is working. But, no power means the problem is in the wiring and not the motor.

Once you have located where the breakdown is, then and only then can you figure out what to fix. Otherwise, you can just throw parts, time and money at it like everyone else until you get lucky and accidently fix it.

 

[Big_John]

One other thing... Remember that the ignition needs to be in the "RUN" position for any of this to work. The headlights will come on, but the doors won't open. Same with closing... If the ignition isn't in the RUN position, the lights will turn off, but the doors will NOT close. Not the ACCESSORY position... The RUN position.

Also BOTH headlights need to be operational or the doors won't close. The relay returns ground through the light filaments.

I've seen this trip up some people into thinking things aren't working correctly.

And speaking of headlights.... Stock wiring with no relays? Correct? None of those LED headlights or something like that either? Correct?

 

[1970FuryConv]

One other thing... Remember that the ignition needs to be in the "RUN" position for any of this to work. The headlights will come on, but the doors won't open. Same with closing... If the ignition isn't in the RUN position, the lights will turn off, but the doors will NOT close. Not the ACCESSORY position... The RUN position.

Also BOTH headlights need to be operational or the doors won't close. The relay returns ground through the light filaments.

I agree with the clicking being the relay and the relay being OK. My 1970 does that sometimes when headlights are on but ignition is off, so HL doors can't open.

I'm curious about the relay returning ground during close thru the light filaments. My relay is installed on the dash shell. I thought it grounded through the shell. Thanks!

 

[Big_John]

I'm curious about the relay returning ground during close thru the light filaments. My relay is installed on the dash shell. I thought it grounded through the shell. Thanks!

It took me a long time to figure that one out... Some time with the FSM etc.

What happens is if a bulb goes out, the headlight doors won't close. I went through this when I added relays to the lights. The relay isolated the headlights, and therefore the ground return, to the relay.

 

[1970FuryConv]

It took me a long time to figure that one out... Some time with the FSM etc.

What happens is if a bulb goes out, the headlight doors won't close. I went through this when I added relays to the lights. The relay isolated the headlights, and therefore the ground return, to the relay.

Thanks. What a strange ground path for closing the HL doors!

 

[Big_John]

Thanks. What a strange ground path for closing the HL doors!

When you think about it, it makes sense as a safety feature. It tells you a headlight is out and even makes it a little easier to change the bulb.

I don't recall seeing it in any literature or manuals though. It's probably mentioned somewhere.