Targa Bar interior light

[BCLi]

Hi all:
I've recently started restoring a 1977 911 Targa. I'm just not smart enough to figure out what is going on. When I got the poor thing, the light was missing from the targa bar. That's the easy part - got one from our hosts. However, the wiring isn't making sense to me. The black wire has power constantly. There are two brown wires, which I assumed were the grounds for the door switches. So:
1. I hook up the black wire to the white plastic end of the switch
2. I randomly chose a brown to hook up. Opened up driver side door - no light.
3. Use other brown wire - same thing - no light.
4. Pull off black wire, and inadvertently touch the metal near the bulb - there is light! I close the driver side door, and it goes out. So there is power, there is a connected ground at least to the driver side door.
5. I pull out the presumed driver side ground, and replace it with the other brown wire - with both doors closed, the light is on and stays on.

So, I have power, I have at least one door ground, and presumably another ground. What am I doing wrong in that I have to bypass the connector to get at least the driver side door working? Is there a switch of some sort? (I know on the coupe there are rockers, but I don't have that on my targa light.) And I must also be doing something wrong since there are two brown wires but only one way I can make the light illuminate. Any help for this newbie would be greatly appreciated! Thanks!

Bert

[rwest]

Hi Bert,

Not sure on the wiring, but even though it doesn’t have a rocker, it does- light itself has 3 positions: on, off and door open on.

So likely one brown is always to ground and the other goes through the door pin switch.

Hook it back up and then pivot the light and you’ll probably figure it all out.

Rutager

[tmadden2]

The switch has two different ground terminals. The middle "flat" position is off because it's got power going to it, but no ground contact. Moving the switch to either position completes the circuit to light the bulb. One grounds to the roof for the "always on" position. The other is tied into the door switches to light when either door is open. If one of those is messed up, it leads to all sorts of quirky behavior with the dome light and power windows.

[BCLi]

Originally Posted by rwest

Hi Bert,

Not sure on the wiring, but even though it doesn’t have a rocker, it does- light itself has 3 positions: on, off and door open on.

So likely one brown is always to ground and the other goes through the door pin switch.

Hook it back up and then pivot the light and you’ll probably figure it all out.

Rutager

Thanks Rutager. I didn't realize the light is a rocker. So I attached the black wire to the switch, the door pin ground to the other end, and rocked it fore: light! Center seems to be off.
I attached the other brown wire ground to the other spade, which appears to be a ground on the light itself - rocked the light back and forth to the three positions - unfortunately, no joy for constant light. I exchanged the ground wires, and did get a constant light. I can live with that, but in my simplistic mind, since that lights up the light when connected to the light with constant power, when I hook up the constant ground to the ground of the light itself, should I not get a constant light?
Nonetheless, thanks again. At least I have an on/off switch and a entry light.

Bert

[BCLi]

Originally Posted by tmadden2

The switch has two different ground terminals. The middle "flat" position is off because it's got power going to it, but no ground contact. Moving the switch to either position completes the circuit to light the bulb. One grounds to the roof for the "always on" position. The other is tied into the door switches to light when either door is open. If one of those is messed up, it leads to all sorts of quirky behavior with the dome light and power windows.

Thanks - that makes sense. I've confirmed the middle position is off, rock fore (on a relative basis) is door pin ground, and the other brown wire must be ground to the roof. Connecting the ground to the lamp end spade I could get a constant light, but not when I connected it to the light ground on the black frame). I guess the dumb question would be whether the lamp frame needs to touch metal on the roof? In my car, it has been covered with the covering of the b pillar.

Thanks again for the help. Much appreciated.

Bert

[darrin]

Originally Posted by BCLi

Thanks - that makes sense. I've confirmed the middle position is off, rock fore (on a relative basis) is door pin ground, and the other brown wire must be ground to the roof. Connecting the ground to the lamp end spade I could get a constant light, but not when I connected it to the light ground on the black frame). I guess the dumb question would be whether the lamp frame needs to touch metal on the roof? In my car, it has been covered with the covering of the b pillar.

Thanks again for the help. Much appreciated.

Bert

No, the light frame should not ground to the roof -- in fact, it needs to be isolated from the roof, as it's always getting power from the always on positive (but is disconnected from both potential grounds in the center position) -- the door pin "ground" completes the circuit only when the door's open (causing the door pin switch to complete grout) and turns the light on when shifted to one side -- the light's always on when switched to the other side (causing the always hot ground wire to complete the circuit) -- might want to check the action of the switch with a voltmeter to confirm that both of its circuits work

[BCLi]

Originally Posted by darrin

No, the light frame should not ground to the roof -- in fact, it needs to be isolated from the roof, as it's always getting power from the always on positive (but is disconnected from both potential grounds in the center position) -- the door pin "ground" completes the circuit only when the door's open (causing the door pin switch to complete grout) and turns the light on when shifted to one side -- the light's always on when switched to the other side (causing the always hot ground wire to complete the circuit) -- might want to check the action of the switch with a voltmeter to confirm that both of its circuits work

Thanks Darrin. I will check the switch and see if the continuous ground is working. Thanks very much for the input.
Bert

[jgurnari]

When I carefully took out the door light switch The wire was not there! Fell off in the dreaded black hole! Any ideas how to retrieve it? What is the best access?
Help!
85 911