Stupid Miata Electrical Tricks

I put a ricer carbon fiber trunklid on my 2000.

Now my license plate lights and third brake light don't work. All bulbs are good.

Ideas?

It sounds like a ground issue but I didn't think there was any between trunk lid and the harness separately.

It would certainly be a ground issue if those lights ground to (what used to be) the metal of the trunk.

So apparently, the lid isn't CF, as CF is quite good at conducting electricity.

Or if it is, it's not enough or has a lot of epoxy, which is preventing the electrical components to use the CF as a ground.

Zeitgeist wrote: It sounds like a ground issue but I didn't think there was any between trunk lid and the harness separately.

There aren't any.

GameboyRMH wrote: It would certainly be a ground issue if those lights ground to (what used to be) the metal of the trunk.

I wouldn't think so, but that was my first thought. Sockets are plastic, though. The light itself does not contact the trunk in any way that i can see. Nor do they contact the trunk itself on the 2000 with a stock trunk lid i checked on Monday.

alfadriver wrote: So apparently, the lid isn't CF, as CF is quite good at conducting electricity. Or if it is, it's not enough or has a lot of epoxy, which is preventing the electrical components to use the CF as a ground.

It has a lot of epoxy. It's a good 4lbs heavier than advertised. But i don't see how the lights would ground through the trunk in the first place.

Start testing. Do you have power and ground at the connector where the trunk harness joins? Do you have power and ground on the other side? You had to plug/unplug this connector to install your trunk lid.

A friend of mine had a Lotus Europa that had an "air ground" on the rear taillights. We never did figure out why they worked, there was no way for them to ground. But they worked, so we didn't ask too many questions.

In reference to a good ground like shiny metal on the trunk floor somewhere, is there 12+VDC making it to the bulb? If so, check to make sure there is less than an ohm between the negative side of the bulb socket and that same ground.

Online looking doing quickly makes me think all these bulbs share a ground and that you've got a problem in the harness or in a termination somewhere. Without a good wiring diagram this should be treated as a poorly educated guess unless someone else wants to second this.

Keith Tanner wrote: Start testing. Do you have power and ground at the connector where the trunk harness joins? Do you have power and ground on the other side? You had to plug/unplug this connector to install your trunk lid. A friend of mine had a Lotus Europa that had an "air ground" on the rear taillights. We never did figure out why they worked, there was no way for them to ground. But they worked, so we didn't ask too many questions.

I don't think i unplugged the connector to install the trunk, i just removed the lights and everything from the old trunk, then installed on new trunk once it was attached to the car. I could be wrong. I will definitely check that connector though.

Swank Force One wrote: It has a lot of epoxy. It's a good 4lbs heavier than advertised. But i don't see how the lights would ground through the trunk in the first place.

Trunk is metal. Trunk is bolted to the body. Therefore trunk is grounded to the body. Or trunk = body.

Most lights are grounded with their own bolting systems. Especially low draw ones like the trunk mounted lights.

alfadriver wrote:

Swank Force One wrote: It has a lot of epoxy. It's a good 4lbs heavier than advertised. But i don't see how the lights would ground through the trunk in the first place.

Trunk is metal. Trunk is bolted to the body. Therefore trunk is grounded to the body. Or trunk = body. Most lights are grounded with their own bolting systems. Especially low draw ones like the trunk mounted lights.

You might be right, but i really can't understand how that's possible with the construction of the lightbulb housings in question here. They're all plastic. 100% plastic. The bulbs themselves don't bolt to anything, they're in plastic sockets that twist-lock into plastic housings. Harness itself doesn't bolt to the trunk lid anywhere, nor does it contact the trunk lid directly.

Are there two wires going to each bulb?

In reply to Swank Force One:

I thought there were screws holding in the CHMSL.

T.J. wrote: Are there two wires going to each bulb?

I... think so. From what i remember. Still has the loom and stuff over it though.

alfadriver wrote: In reply to Swank Force One: I thought there were screws holding in the CHMSL.

Goes over two metal M6x1.00 studs. Entire assembly itself is plastic though, so even if the studs were in a metal trunk, the housing assembly would make a dandy insulator.

Honestly i was hoping someone else had had this happen to them after putting a ricer trunk on their car so they could tell me "It's THIS, dummy!"

I really hate poking around with a multimeter.

The internet is telling me the 3rd brake light has a green wire and a black wire, so if that's the case then it sounds like it is not grounded through the trunklid. Since the plate light is also out, I suspect the two grounds tie together and are not connected to ground properly.

In reply to Swank Force One:

With the system off and a bulb out see if either of the wires go to ground. I believe the ground path has been removed by your plastic trunk lid. This can be done without the circuit energized. It will, however, still require a multimeter.

You don't need a meter for this sort of work, a test light will do and is a lot faster and less cumbersome.

Test for grounds by putting the clamp on a good 12V source, probing ground will now light the light.