1987 Carrera Frunk light wiring quandary

[r55forme]

My frunk light has no power, and my car has an aftermarket alarm installed. There is no power to my light when I measure on both terminals, but there is a brown/white stripe wire from the frunk switch with 12v that is just sitting there with no obvious connection.

My clock and interior lights work, so I'm wondering about how the frunk light is supposed to be powered. Its not a huge deal but it would be nice to sort it out.

Here's a photo of what I found



I'm just confused why there's a brown/white stripe wire hanging out with no obvious connection point to the frunk light. Thanks in advance!

MJ

[EC900]

I can’t check mine at the moment - but I think the loose Br/Wh wire connects to the plunger switch. Often disconnected because it’s easier to unplug wire than open the bulb lens to pull out (hot) bulb when leaving hood open.

[WMichelsen]

Are you missing the switch?
That brown/white is power crimped onto the switch (I think).

[dictoresno]

yea it looks like the luggage compartment light switch is wired into the alarm/anti-theft control switch via a brown/white wire. are you missing the switch or did the wire just get ripped out? id imagine, unless your aftermarket alarm has this bypassed, it would be triggering your alarm nonstop.

now I understand why my dad had his Clifford alarm removed and the car reharnessed back in the early 2000's. too many electrical issues with an aftermarket alarm installed parasitically over the OEM alarm.

[r55forme]

Nope I have the switch, that brown/white stripe wire is connected to it. When the switch is open I get 12v, when its closed I get nothing. I assumed that should trigger the frunk light, but heck if I can see how it would have connected.

It is a bare wire just hanging out there. So if the switch doesn't trigger the frunk light what does? My interior lights are on, but I have no power at the frunk light terminals.



I guess it doesn't really matter, but just wanted to understand how it should work

Thanks!

Oh and I hate the alarm--it passively arms are 30 seconds even if the doors aren't locked. Super annoying as I set the damn thing off in my garage when I just open the car and forget.


MJ

[Winter]

Just a “hack” to consider when you have your specific issue sorted.

People disconnect the light due to battery drain when the Frunk is open, during work on the car, for example, etc.

You can use the correct length of wood dowel against the “pin” to keep the light off, friction fit style.

Cheers

[EC900]

No telling if that wire was accidentally yanked out by someone doing a hood removal, but the sheathing is missing too and if it’s hidden or tucked somewhere it might hold the other half of the wire, keeping it from shorting.
Check the right corner and look for any empty terminals, they all should be mated up and it’s where they go to the cabin lighting.

This is on my ‘77 (no alarm Wh/Blk wire) ….

[wazzz]

Black wires carry permanent power (+12V), while brown/white wires are switched grounds.
Here is an annotated diagram from the factory diagrams.

[r55forme]

Thanks Giles,

Electrical is an area I'm easily confused in, so the diagram is helpful. Excuse my ignorance, just want to make sure I understand. What is NR 44? It somehow is getting power to my switch and hidden in the hood?

1. Based on this, I have 12v on the black wire coming into the light
2. Broken ground between the light and the switch
3. Because the ground is broken, I get no voltage across the light terminals
4. If I put the multimeter to ground, I should register 12v at the black wire part of the light?

If that's all true, I'd just like to see the wire path the switch ground takes to connect with the light ground.

Thanks for the idiots explainer.

I guess the break would be after NR 44 not before, in my markup.

[ccallana]

Originally Posted by dictoresno

now I understand why my dad had his Clifford alarm removed and the car reharnessed back in the early 2000's. too many electrical issues with an aftermarket alarm installed parasitically over the OEM alarm.

One of the first things I did with my car is to pull the Clifford out. I left the LED in the dash - I suppose some day I could wire it up so it flashes

[wazzz]

I'm trying to figure out your issue, but am not sure to understand everything (my English, I guess). So a few questions to clarify:

1 - Where does your dangling brown/white wire connect on the diagram? Please edit the diagram to show it.
2 - Is your bulb filament OK and is the bulb still installed? If so, when measuring with red probe at bulb black wire and black probe touching a metal part of car body (a known-good ground), you should read 12V.
Now keep black probe on metal part of car body and bring red probe on the upper terminal of switch (the one that has the brown/white wire on the diagram). You should still read 12V, because voltage is measured through the bulb filament and since there is no current flowing, their is no voltage drop at the bulb, so 12V power is present at both upstream and downstream of bulb. This is with reference to ground taken on car body. This is also with brown/white wire still connected between switch and lamp, but since this may be the dangling wire I am asking about, this second measurement may not work.

3 - As for the NR44, this is the sheath (loom) number. This does not convey current, so the green line that you added on the diagram is wrong.
Current can only flow through the bulb then the switch when closed. Otherwise no current, no voltage drop.

[r55forme]

Giles, it isn't your English, its my explanation

Thank you for the 12v measuring guidance. In my initial measuring, I did not put the black to body ground, so I will do the 2 measurements tonight and report back.

I put a new bulb in, measured at both the brown/white and black terminals, and I have 12v at both. And the light doesn't come on. So I'm guessing one of those brown/white wires in the loom was cut, and pulled back to not ground out? I will have to take it apart a bit more and see what I find.

Here's my diagram, and thank you for educating me on how to diagnose it.

[r55forme]

Here a photo of the light fixture out, the loom and the broken brown/white wire

[wazzz]

Originally Posted by r55forme

Giles, it isn't your English, its my explanation

Thank you for the 12v measuring guidance. In my initial measuring, I did not put the black to body ground, so I will do the 2 measurements tonight and report back.

I put a new bulb in, measured at both the brown/white and black terminals, and I have 12v at both. And the light doesn't come on. So I'm guessing one of those brown/white wires in the loom was cut, and pulled back to not ground out? I will have to take it apart a bit more and see what I find.

Here's my diagram, and thank you for educating me on how to diagnose it.

OK, so that confirms that permanent BAT +12V is present where it should. And you can see it both upstream and downstream of bulb because there is no current flow, hence no voltage drop. If you were to measure voltage between both bulb terminals (and not between one of them and body ground) you would find zero volts (no voltage drop).

I guess the dangling wire should indeed be reconnected to the terminal that has the two brown/white wires, as that is where it belongs.

To make sure, take a piece of wire, preferably with crocodiles if available and make a temporary connection between the dangling wire and the lamp terminal that has the two brown/white wires. The bulb should go on. Press the switch down and the bulb should go off.
This test would confirm for sure that you need to fish the other part of the wire inside the loom and reconnect it to the dangling wire.

[r55forme]

Giles thanks for all the help. Surprisingly, jumpering did not light up the bulb. I think at this point I'm just going to cover the exposed end and put the light back together and try and figure it out later when I am bored and have nothing else to work on. Clearly there is some else in the wiring I'm missing but since all my other interior lights work the frunk light isn't all that important.

Until then, thanks again