Here's how dome light works. It gets power directly from a fuse. When door is opened or light switch turned to dome on position, either the door switch or headlight switch provides the ground needed to light the dome.

If dome was working then stays on first see if the door switches are grounded without the door being opened. Remove wire from door sw to test. Do both door switches. If that doesn't fix it try the headlight switch to see if it is grounded for dome operation.

If that still doesn't fix the dome staying on, try removing dome light from roof and letting it hang. Does light operate normally with door switch now? If yes, your new dome light has a short to ground.

If no, ground wire running to door switches or headlight switch is grounded someplace.

Here's the thing about a ground wire. If it is shorted to ground anywhere along it's length, dome light will be on.

See if you can find a 70 wiring diagram to help you with wiring colors and routes. Maybe one in 2nd gen tech section.

 

I agree with sea dog. Check for grounding issues first. If it's not that, then you may need a new door switch. The old Esprit has a problem with the dome light too, but opposite yours, it doesn't work at all. I'm not ready to take the headliner out to fix it yet tho, haha.

 

So the oddest thing...as i was about to trace down the grounding issue on my dome light, my LED bulb was dropped off by fedex. So i removed the Incandescent bulb, installed the LED, and now the dome light works as intended (only one when door opens). I switched out the bulbs a couple times to confirm and sure enough, when I have the LED bulb in place, it works as intended. When i put the incandescent back in, dome light stays on even with doors shut. Weird but problem solved!!

 

Yeah, Ive always heard that mixing diode's with incandescent was not beuno.

 

Derrick is correct. L.E.D. lights are polarity sensitive (+) & (-) sensitive. Mixing the two in the same circuit does funny things. I work as a semi truck mechanic and find that as you see semi trucks & trailers switching to these newer L.E.D. lamps, when they mix them, it does some wacky stuff, especially in the turn signal circuit. Since the LED's light & shut off at a much faster rate the an incandescent, the turn signal relay (which clicks on & off based on the "heat" or resistance in the circuit) doesn't know how fast to click, which usually results in the turn signals flashing as fast as a strobe light, or really s-l-o-w-l-y, or not at all !