Interior Lights Not Activated by Door Opening

[Paul S Zuchowski]

If you pull out one of the lights, you will typically find two wires. One is "hot" and the other is the door switch wire. The third connection (ground) is local to the light. I say typically, because sometimes somebody will run a short jumper to a sheet metal screw for the "always ground" instead of relying on the friction connection between the light fixture and the car body. On my left hand light, the two wires come to the connection point as a bundle. The bundle splits out to individual wires at the connection point. When you test your door switch, make sure the light is in the correct mode.

[Dave Erickson]

Doug, thanks for posting the circuit diagram. Since neither door switch activates the lights, and all three of the lights do not illuminate, that points to a single point of failure. With reference to the circuit diagram, it would be in the center top wire that connects both door switches to ground. Where does that wire run? Where is the ground point?

[Mike Wilson]

Correct me if I am wrong but don't the door switches, when the doors open, complete the ground?

Mike

[Wes Bender]

Correct Mike. Either door.

[Douglas Carrie]

The local grounds seem to all work - all three lights can be placed in an "on" mode. I'm a bit confused by my last attempt - somehow the driver door switch was working ..... for a while! I don't know if it was just a coincidence but the clock suddenly rewound its spring (yes, original clock and it does work!). At that precise moment the door activation stopped!

Roof light was in the middle position which should be on all the time. Dash light was in the back position. The door switch was switching them off in those positions. That was two days ago. Checked them today and door switch worked! But...roof light was in middle position. Suddenly door switch stopped working when I closed the door - the lights stayed on. I was pressing with my hand on the door switch with earlier checks.

I think I need to document what happens in a more closely controlled effort. At least I'm learning more than I ever thought I would about interior lights.

[Mike Wilson]

The clock and cigarette lighter have a common hot wire. I found the clock is very sensitive to ground. I run a separate ground wire from the clock bracket stud to a bolt in the wiper motor bracket.

Mike

[Martin Benade]

On all the time should mean the light is grounded locally all the time, and door switch ground should be meaningless. Are the connections reversed at the light?

[Greg Bryan]

Doug - you're right - you'd think you'd be hard pressed to fill two pages on the Interior light circuit, but here we are.
I'll summarize what I've read here so far.

• The Interior light assembly has a three-position switch - Off; On; and Door. It has to be in the 'Door' position to come on when the door is opened, and lights are independent, i.e. if one (or both) is in the Off position it won't come on. (Not sure if older cars have this same switch arrangement)
  • The Interior lights have power to them all the time. Switching is all done on the ground side.
  • There are three sources of ground to turn the Interior lights on. First is the unreliable local ground that comes into play when the switch is placed in the On position. (I had to chuckle at Paul's comment above as I did just what he said, ran an actual ground wire to make it reliable - I have a cab and it only has one interior light) The local 'On' switch will only turn on that individual lamp.
  • The other two grounds are the right and left door switches which come into play only when the lamp assembly switch is in the 'Door' position. This circuit is wired such that all Interior lights will come on - if the switches are all in the Door position.

• The door ground switches are susceptible to having a poor ground connection because of buildup of paint preventing it from reaching bare metal. Some people use a serrated washer between the switch and the body to insure a ground connection.

Actually, since I have a cab, I'm not certain if all coupes have the center interior light, or only the two lights up in the roof by the B pillar.

[Martin Benade]

Some versions of the dash light have a tab for a ground wire to push on.
I wonder if Douglas has that kind, and the door switch wire is on the terminal meant for the “always on” ground wire.

[Douglas Carrie]

Test Case 1:
Turned dome lights to on position and dash light to back position. All were on. Pressed door switch with my hand. Lights went out. Released lights went on. Closed the door and lights stayed on! Pressed door switch with my hand and they didn't go out but did dim slightly.

Next I'll check wire placement per Martin's comments.
Thanks everyone for your guidance!

[Greg Bryan]

I believe there should be a small rubber puck in line with the door switch to push it in further. Although is sounds like there is more to figure out in this case - maybe the door switch itself is faulty. You could try pulling the wire to the door switch (I know it's hard to get to) to see if the light goes out. And, if you have the wire in your hand, you can test it to see if the circuit is working as designed. If the light goes on and off as you ground and un-ground the wire, you have isolated the problem to the door switch.

[Mike Wilson]

Greg is correct. There should be a round rubber pad about the size of a quarter on the door where the switch button hits.

Mike

[Douglas Carrie]

One correction so far - Greg's comment about the missing "puck" answers why, when the switch works, it doesn't work with closing the door. Thanks, Greg! I assume that when the car was restored back in 2012 the puck was not placed in the door. Off to Stoddard/Pelican/SMC I go!

[Douglas Carrie]

Second clue: enter car after ~20 hours of "rest" - place dome light in always on position (center position) dash light in back position and both lights are on. Manually press door switch and lights turn off. Repeat several times and lights turn off each time. Clock does its "reset" and now door switch only causes slight dimming of lights but they stay on. This repeats what I described earlier but a little more controlled.
After some "rest" I'll try some other electrics such as the headlights...IF the interior lights are back in the door switch activated mode. Per Martin's suggestion, the fact that the dome light is door controlled in the middle position makes me wonder.

[Martin Benade]

Does your dash light have two or three connections? I think the three connector one could have power and ground swapped making it act this way, and not blow a fuse. This is a theory, might be all wet.