OK, I know this one seems simple but before I get into it and invent New Bad Words that my kids shouldn't hear..... I figured I'd just test my thinking. My 87 custom 2x4 regular cab had the standard interior dome light. Door opens light comes on. So, since I have rebuilt the truck and have upgraded where possible for a little more cozy ride, I got a light from the salvage yard, "the two reading lamps" with the interior light that comes on when the door is open in the center. Now my reading lamps work fine, BUT the interior light only comes on a little bit....I put an LED in it and it just barely lights. I am thinking a bad ground? or is there something about the reading light set up that is different? Any advice would help...Not a major problem, just one of those nagging things... Thanks

 

Which kind of dome lamp did you install?

 

I put the second one you showed in. But if I see your picture correctly there are only 2 Screws holding it in. I have three, Maybe an extr screw is grounding it?

 

Check for available power to the bulb socket, should be battery voltage (12.5 ish volts) when you turn the switch for those lights. Check ground via resistance, should be less than 5 ohms. Also, inspect the light bulbs themselves for corrosion/rust at the base which could cause issues.

 

You need all three screws installed. The screws are where power and ground for the lights are connected. The two rectangle shaped screw points are power for the lights; one will be hot all the time, the other is hot when the door is open, or the headlight switch is rotated counterclockwise. The round screw point is the ground.

This is also the same for the plastic dome lamp pictured above. The wiring is the same for both.


An issue I've had with this light is the bulb contacts make poor contact with the bulb leads. The white plastic surrounding the contacts can be removed, and the springy bit of the contact adjusted to make better contact with the bulb.

 

OK, so what I did... I pulled the light down on Saturday and pulled the entire wire harness out of the roof. I inspected for any damage that may have occurred when I put it in (I replaced the old harness since it was pretty chewed up). I then connected all the wires and I ran a good ground to a bolt under the dash with the light just laying on the seat. As soon as I connected the good ground (using a nut and small bolt in the ground location) the lights all worked perfectly. BUT when I put the light back up above in my truck, it went back to not working. This time the Interior light stays on at all times. I may have the (Constant Hot) and Door controlled reversed, BUT the reading lights work fine. I need to check to see if they come on when the door is closed ie.. no power.. (just thought of that) they work when the doors are open, which which would be correct if I have the wires reversed. If that isn't the issue I will take it down again, recheck to see if it works and if it does then I need to attach it to the roof without grounding it and just use the good ground as the ground for the light... It's not a big issue, but just one of those nagging little things that drives you nuts...

 

Or, you could address the ground problem properly. You either have a bad ground at the light, which only effects the light, or a bad ground between the cab and the battery, which will effect anything that uses the cab as a ground. I don't know where all of the ground locations are, but someone who does could post a diagram of the ones relevant to the dome light.

 

Ok, thanks for the advice. I connected a good ground from the cab to the frame and that solved the issue. Can't believe it was that simple, but I had one good grounding cable I had bought but not yet used left, and I used it make a good ground to the frame. As soon as I did everything worked perfect. Thanks again.

 

where was that dome map lights wiring routed at? im having a issue with no map lights but my domes fine, the bulbs fine and the fuse fine, im thinking its a wiring issue like maybe a plug came off the constant hot for the maps.. anyone know where the plugs are at for the maps? is there a plug for the harness by fuse box? i have a 89 crewcab

 

I put the reading light setup in my truck, upgrading from just the Dome light. The problem I had was I could get my reading lights to work but not my Dome, then I pulled the harness out and made a good ground with the hot wire attached in the harness like it should be... EVERYTHING worked great. When I put everything back in place it didn't work again. So I went under the truck and attached one ground wire from the cab straight to the frame and have not had a problem since then. As far as the routing, the harness connects under the trim at the front of the dor (near the Hood Release), it runs back in the channel under your door sills, then up inside the cab frame and over to the bed light and dome light. The two wires fit into plastic snap fit pieces that your dome light screws screw into. Hope that helps.... But try the ground, It drove me crazy for a couple weeks I couldn't believe a simple ground could do that much.... it did, I learned my lesson.

 

well thats probably where my problem is under that door sill plate as i have a rust hole there. ill have to pull the plate off and check, thank you.

 

Wiring for the dome light should go down the driver's B pillar to the floor.

Quite often there is a lot of moisture there at the floor area.
This is where I would look, with a test light in hand, to see if there is any corrosion or bad wires, before tearing things too far apart.

Edit:
not sure about pre 92 or crewcab but probably similar

 

another vote for peeking under that sill plate. at the very least it gives you an opportunity to clear a half-cup or so of gritty muck outta there and in the process you just might find a compromised wire.

 

well guys problem solved, i feel like a super moron. i didnt realize the light switch on the dash had to be in parking light mode or headlight mode!! durr i guess they worked all along!

 

Actually, problem not solved. The map lights are supposed to have constant 12v to them. They work whether the key is in the ignition, or not, or at any position of the headlight switch.