Interior lights problem w/ video explanation

[Stainless]

I'm looking for help in figuring out why my interior lights don't work like they should when the doors open and close. I fear the PO may have modified the wiring for something else, but I am not sure. See the video below for a description:

[DrJeff]

I'm looking for help in figuring out why my interior lights don't work like they should when the doors open and close. I fear the PO may have modified the wiring for something else, but I am not sure.

I would look at your Interior Lamp Delay Unit first. I believe it is the white relay in the front-most row in the relay compartment. (link to SpecialTAuto reference page http://www.specialtauto.com/delorean...eferences.html ) My car does not have the stock unit anymore so I can't check. You will also want to double-check the connections to the lamp units (both front and rear). When I got my car one of them had been re-connected incorrectly. The result was that they only worked in one mode. Here is a link to the connection reference (link to SpecialTAuto reference page http://www.specialtauto.com/delorean...tsey-light.jpg )

[Ron]

The drivers side switch should have a Black and a Purple/Pink wire. It looks like the PO may have added the Red wire because the Purple/Pink wire was bad (or could be for an alarm system?). Trying it with the Red wire disconnected might reveal a lot (check Door Ajar Light operation too)... You might find the Red Wire spliced in at the Interior Lamp Delay Module (looks like a White Relay, 3rd from the left). It's common for this module to go bad, be removed and jumpered with a popular modification.
There are three diodes stuffed to the right of the accelerator pedal and are known to have bad solder joints. (They are, black, round, ~dime size diameter, and ~couple inches long. Check them by seeing if the have continuity in one direction but not the other when you switch ends with the meter test wires. Shake them when testing!)

The wires to the front courtesy light are correct.

Is it safe to assuming the lights act the same way when operating the passenger door?

Full Wiring Schematic Here

[Rich]

Another wiring diagram, specific just to the door lights, interior lights, is at the bottom of the first post in the link, corrected and you have to click on it to open it.

http://dmctalk.org/showthread.php?40...ing-Schematics

Not different from the full wiring diagram, just broken out for easier digestion.

[Farrar]

From the Owners Manual, re: dome light operation.

Forward Switch Position: Light operates when either door is opened. In this position a delay unit will cause the lights to remain on for approximately 10 seconds after the door is closed.

Center Switch Position: Light will remain off regardless of door position.

Rearward position (as illustrated): Light will remain on indefinitely.

So it looks like you're only missing one function of the dome light -- the one that relies on switched ground (purple/white). It seems one of the grounds which should be switched is not switching. Try putting jumpers in place of your light switches and see if you can troubleshoot from there.

[Bitsyncmaster]

Your problem has to be at the diodes since you have power on the purple wire. Make sure all three diodes are good and plugged in. The PO may have blown a diode out with his wiring modifications.

[Ron]

I'm guessing a diode(s) too. But why wouldn't a bad/missing Delay Module, or a bad connection to it (P/W or B) act like that?

[Bitsyncmaster]

I'm guessing a diode(s) too. But why wouldn't a bad/missing Delay Module, or a bad connection to it (P/W or B) act like that?

Delay Module just keeps the light on. A bad module would only not keep it on or keep it on all the time.

[Jonathan]

If you peer in real close to those dome lights, you can see which metal tabs are moving when you tip it back and forth. They can sometimes get loose and the metal doesn't touch anymore.

We know your bulbs are okay, as is the always on power and the ground. If the mode to turn the bulb on with the doors is not working, have you confirmed there is 12 volts to that wire? If your other interior lights are on with the doors open, like the instrument cluster 'door open' light, the door lights themselves (3 per door), then you should have 12 volts there. You can test it with a multimeter, or take that wire off, take the bulb out, touch one end to the ground and the other to this now loose wire, and see if the light comes on.

If there is no power there, then it could be something with the delay relay or the diodes already mentioned, or a short somewhere (although not as likely since both front and rear lights are doing the same thing).

[Rich]

Your problem has to be at the diodes since you have power on the purple wire. Make sure all three diodes are good and plugged in. The PO may have blown a diode out with his wiring modifications.

+1

And one or more of the diodes can just die after so many years, even without anybody fiddling with the wiring. The diodes are easy to find and check. NOS diodes are readily available.