There isn't a fuse on the horn circuit. Direct feed from battery, same point where the lights are...

The schematic tells all that...

New enough, they have. At the top of B-pilar...

On the firewall driversside there are a bunch of small connectors. Check if they are corroded, might cause your interior light not working.

OOPS forgot about that. No wonder the circuit kept on working!

Found it! I pulled the felt back enough and there is it.



And I bet the wire is amongst these other green wires I wrapped up with electrical tape:



Now I just have to figure out which one of these green wires powers this overhead light and from what circuit it connects to. I have a wiring diagram at the house so I can look that up later.

I'd really like to add a door jam switch so it turns the light on automatically. Any you guys ever done this? I've got an idea but it's a bit hard to explain.

just look to the color of the connector under the bonnet there will be a red one too normally.

I verified that the brake lights are working.

The wiring diagram shows this done light wire makes a connection before the brake light switch. According to the diagram it's a continuous wire. No connectors between the light and the brake switch.

Also it's saying at some point the wire changes color from brown to green.

So you are saying this wire connects under the bonnet and there is a red wire connected to it?

Well now I am stumped!

I got home giggled the "always hot" wires at the fusebox (despite everything else on that circuit working fine and I have replaced all connections in the engine compartment and even the fusebox anyway), giggled the wires at the brake switch (only two). Still no signs of of where this dome light wire originates from.

Now I am getting full voltage at the wire going to the dome light! ~13.2 at the battery and 13.0 at the wire, engine not running.

I wanted to rule out a bad earth so I connected the negative side of the meter directly to the negative post on the battery when I was getting 6 volts. But who knows, maybe I was getting a poor earth all along.

I do know for sure that the dome light housing is not getting a good earth. It has to be positioned just right in order to get it work.

How is this housing supposed to get earth anyway?

I did not take a photo but the housing has a small hole in it, as if a screw is supposed to go through it in order to hold it in place but to also provide earth.

I cannot find any threaded holes in the frame above the door. I poked around with a dentist's pic through the felt to no avail. So I pulled the felt back and still cannot find any threaded holes!

Like I said there are not many cavities or double layers or metal on a 2CV so if I tried to drill a hole, it would go straight out the other side.

I think I am going to do away with this cheesy little light altogether and use the LED strip across the support bar, earth it to the body but use the unused rear fog light toggle switch in the instrument cluster to turn the strip on and off. That way it only works when the park lights are on.

One of these on a round surface may ground the wire.

https://www.ebay.co.uk/itm/GENUINE-JUBI ... IEY1JCIZUA

Don't forget, electricity, won't go through paint.

I've not seen one of these lights before, may I see some photographs please.

@turbofiat124
Scrolled through your photobucket photos, very tidy car , like it.