Unfortunately, there is no quick and easy plug and play harness near the headliner for installation of the OEM Roof Marker Lights.
In the official instructions, how they have you do it is you have a positive and negative wire down the windshield, under the plastic A-pillar. From there, the black ground wire goes into the engine bay into the main interior wiring harness behind the battery, where there are six blunt cut wires all bundled together sticking out from that large wiring harness that are in various different colors, such as orange, green, brown, black. They have you connect black ground wire from the roof marker lights and connect it to the blunt cut wire, but personally, I find it easier just to add a wire terminal loop and connect it to a dedicated battery ground that is found very close to there on the driver side inner fender mount.
Now, for the positive wire, this wire keeps going and plugs in under the fuse box. Now when GM originally made the Fuse box for the H3, they made a hidden place to plug in a 8 pin GM Specific connector to under the fuse box for the GM Genuine Accessories which included the OEM Roof Marker Lights, OEM Offroad Roof Lights, and the OEM Grille Lights. This came on every single H3 because no H3 from the factory had any of the roof lights or grille lights installed. These were all dealership installed options. Because there were 3 different accessories that were able to plug into the same connector, GM had different pins that these wires would occupy in the 8 plug harness. In the case of the OEM Roof Marker lights, the connector that plugs into the Fuse box is just a single red wire. The reason why you want to plug into the fuse box with this connector is that it supplies the running lights signal so the OEM Marker lights will work normally just like the side markers, corner lights, and rear tail light running lights. If you don't already have the full harness that the roof marker lights originally came with it can be tricky to find that 8 pin plug these days. It goes under the part number P2094. I believe it has been discontinued, but I think there are a few other superseded part numbers that possibly have that plug. Typically when I need one I got to a Junkyard with an H3 can take the hvac resistor wiring harness plug or power seats plug because it is the exact same 8 pin plug. But anyway once you plug that connector to the fuse box you are good to go. You do need to take out the fusebox to actually be able to plug it in. To do that you have to remove the air inlet hose that goes to the battery, remove the fusebox cover, disconnect the connections to the fusebox, and then slide it out by releasing the tabs and pulling up on it.
Honestly, it sounds more complicated than it actually is. If you are serious about doing this, I have a lot of pictures and stuff I can send you on it. You can reach me better at on Facebook which is Acer Miller and My Instagram is
@Acer4LO
). I've already had the fuse box out and I think I remember that 8-pin you're referring to (I figured it was for diagnostics but I had bigger fish to fry at the time). In any event, having the cab lights work in unison with the corner/running lights is exactly what I was going for. These are not the OEM lights for the H3; I got the single-center/2 side lights similar to that found on Silverados/Sierras. Turned out exactly how I imagined it would, too.
