3 wire map/dome light retrofit

[mickeykreg]

I've got a dome/map light combo out of a 96-99 tahoe. Trying to slam it into a '77 blazer. Just wanted to run this by you all. This is what I've done and it works, but don't want to assume it's correct. Thoughts?

I found this old thread, but the suggestion doesn't work in my case.
http://67-72chevytrucks.com/vboard/s...ht=3+wire+dome

[67 Burb]

If the wiring is as you have labelled in the photo, where do the reading lights ground to?

I have seen a dome/reading lamp where all three were powered from the same source with the hot to the reading lights switched and then grounded thru the mounting screws.

The black may be the power for the reading lamps, but then are they grounded thru the screws?

[Eightball1978]

I'm not positive but I think that's a jumper to make them both come on with the doors I think. If you need a little light in the front mid to late 90s GM trucks and cars have a rear view mirror with to map lights. I use them on just a bought all of my older trucks they don't look to out of place and can be hooked up straight (flip switch) or same place as dome light.

[mickeykreg]

Originally Posted by 67 Burb

If the wiring is as you have labelled in the photo, where do the reading lights ground to?

I have seen a dome/reading lamp where all three were powered from the same source with the hot to the reading lights switched and then grounded thru the mounting screws.

The black may be the power for the reading lamps, but then are they grounded thru the screws?

Both lights ground (through the same wire) and come on, when you open the door, or turn the head lights switch counter clockwise all the way to power on the dome with the doors closed.
I thought originally that there was one hot and two grounds, but that didn't work.

Thanks for the tip on the mirror. I didn't realize they had map lights on them.

[67 Burb]

Well, if you wire it like you say, then you couldn't have the map lights on without having the dome light on first. (With the door open or by the headlight switch.)

Here's the wiring in GM cars in '84. Yours will work if you rewire it like in the schematic.

[mickeykreg]

Originally Posted by 67 Burb

Well, if you wire it like you say, then you couldn't have the map lights on without having the dome light on first. (With the door open or by the headlight switch.)

Here's the wiring in GM cars in '84. Yours will work if you rewire it like in the schematic.

So, per the schematic, orange is hot, white is grounded to the door switch, and black is body ground? I'm pretty sure I tried that, but maybe had a bad ground.

[Black_Sheep]

Originally Posted by mickeykreg

Both lights ground (through the same wire) and come on, when you open the door, or turn the head lights switch counter clockwise all the way to power on the dome with the doors closed.
I thought originally that there was one hot and two grounds, but that didn't work.

Thanks for the tip on the mirror. I didn't realize they had map lights on them.

When you rotate the light switch to turn on the dome it is actually grounding the dome light to complete the circuit. I wired mine up with a relay using door jamb switches or the headlight switch to ground the relay and power up the dome light and under dash courtesy lights.

[67 Burb]

Originally Posted by mickeykreg

So, per the schematic, orange is hot, white is grounded to the door switch, and black is body ground? I'm pretty sure I tried that, but maybe had a bad ground.

Yes, correct for the orange and white. In the schematic I posted, the map lights ground is switched to the metal body of the lights which in turn is grounded to the vehicle body. But it looks like the lamp body of yours is plastic.

You would have to rewire your unit like this and then the red is constant 12 volt, the white (dome ground) to the light switch / door switches. And the black to vehicle ground. So then all the lamps will have power to them all the time, with the dome will work as normal and the reading lamps turn on when switched on (to ground).

[67 Burb]

Originally Posted by Black_Sheep

When you rotate the light switch to turn on the dome it is actually grounding the dome light to complete the circuit. I wired mine up with a relay using door jamb switches or the headlight switch to ground the relay and power up the dome light and under dash courtesy lights.

Yes, that's how GM courtesy worked for decades, but it looks like the unit Mickey has wasn't wired that way because all the grounds are connected. I've seen a lot of people get really confused when it comes to dome lights because they're not used to switching the ground side of the circuit.

For his unit to work, he would have to do your trick with the relay for the dome light red wire and supply 12 volts to his black wire. Then the white would be ground for all three lamps.

[1967GTO]

According to the 1998 service manual schematic, the black is ground, red or pink is 12 V, and the white is to the door jamb switch.

[homemade87]

These lights are different that our trucks and are wired different . This light is not ground triggered . This is why all the grounds ( white wires) are all wired together .

This light is only wired for the center dome to come when the door is open +12 . The maps are independent and when switched they will stay on until they are switched off . If you want all three to come on when the door opens you will have to use a relay also .

Using the connector for reference to get this to work with your ground trigger with the three wires ( white, red, black ) .Make the black wire and red wire +12 all the time . The white wire will be a ground all the time . To get the dome to work clip the white wire loose from the dome light where it ties into the other white wires and attach that wire to your ground trigger from your truck . This will make the dome only work when the door is open . This light was not made for all three to come on at the same time with the dome . Use a relay if you want this to happen .

This may be another option for you .

[mickeykreg]

Originally Posted by 67 Burb

You would have to rewire your unit like this and then the red is constant 12 volt, the white (dome ground) to the light switch / door switches. And the black to vehicle ground. So then all the lamps will have power to them all the time, with the dome will work as normal and the reading lamps turn on when switched on (to ground).

Finally got time for messing around with this. I did exactly what you said and it works fine. Not sure why it was so complicated to me. Thanks for taking the time to explain things.

[67 Burb]

Glad I could help.