Does a 1933 Plymouth Dome light work off only the switch or does it need other power as well?

[auburnseeker]

Working on my 1933 Plymouth PD coupe.  I have everything working except the dome lamp.  I have a good ground but can't get power at the socket.  Do the headlights, dash light or ignition need to be on as well, or does it work independently off just the switch on the light? 

[Xander Wildeisen]

A stock wiring diagram will tell you. Switch should turn it on, and most likely turning the head light switch. Or some other switch the driver could do while seated in the car.

[auburnseeker]

I unfortunately don't have the wiring diagram as it didn't come with an owner's manual.  I figured some other switch probably needed to be on as well,  just wasn't sure which and didn't want to kill the battery or fry the points messing around with stuff. 

Headlights were all messed up,  but I got those working properly. Seems someone installed one of the bulbs upside down. (they are possible to do that) Pulled my hair out until I figured that out,  as I thought I had a short in the harness,  by the draw I was getting and the lights not working right.  Corroded terminal on the headlight switch didn't help either. That configuration also shows a connected circuit between Hi and low beam,  which I didn't understand was possible until i saw the bulbs and the way they are designed. 

Edited July 9, 2022 by auburnseeker (see edit history)

[28 Chrysler]

I don't think it needs to have any of the lights on. You may have a bad switch, test for power to the switch if you don't have 6V there you will have work back to the dash.

I attached a download  there should be a fuse also.

Edited July 9, 2022 by 28 Chrysler
attachment (see edit history)

[Xander Wildeisen]

Looks like it is fused and powered straight off the amp meter. Power should be at dome light. With switch on dome lite controlling it. Bad ground, fuse, bulb or switch. Also clean connection point/terminals on power supply. Corrosion is another reason for loss of power. Resistance builds heat.

[Scott Bonesteel]

99 times out of 100 it is a bad ground. Power is always at the switch and when you throw the lever that feeds through to the ground, which lights the bulb.  I have seen that wire ground just go to the chicken wire in the top, which is often a less than perfect ground.  Need to run the ground wire to the body at the edge of the top insert.  I went a step further on my 34 PE sedan and wired the ground wire to switches in the door jambs so the ground is provided when the switch is opened at the doors.  Not totally original but a nice feature to have. 

[Xander Wildeisen]

If grounding to the chicken wire. You might get the effect of a radiant heated floor.😂 I have noticed the headliner is warm to the touch. When my dome light is on.🤔

[31plymouth]

Almost had a major fire in my 31 Plymouth because of a faulty dome light switch.  Others have also had problems with dome light switches. 

 I disconnected mine many years ago.

[1932 plymouth pb sedan]

If not working properly, I would suggest running a new ground wire and it will work as new. The chicken wire in the roof is not grounded and was used as a radio antenna.

[ply33]

To reiterate some of the above:

• Power to the dome light is from the fuse holder on the back of the ammeter. It is always on.
• The power wire runs up the driver (left) side "A" pillar then above the front door where it makes a 90° bend to go to the dome light.
• The only switch is the one on the dome light.
• The ground wire runs to the passenger (right) side where it is grounded to the car body.
• The chicken wire on the roof insert is not grounded. There is a wire connected to the chicken wire which runs down the passenger (right) side "A" pillar where it is available as an antenna connection (the chicken wire is the antenna) if the accessory radio was installed.

[auburnseeker]

Thanks for the help.  I'll try to check the other side of the switch.  Working with the original headliner and not trying to damage it in the process.  Thanks for the wiring diagram as well.  I found and checked the fuse, that was fine of course as it runs several things and everything else works.  I checked ground even before posting as the insert in the roof was replaced,  so I thought maybe they disturbed something,  but it has a good ground. 

I'll use the wiring diagram to confirm I'm chasing the right wire under the dash and post back on what I find tomorrow.

 

The ammeter doesn't show any discharge when I play with the switch so it's not dead shorted. In fact no matter what I did,  it never showed a discharge so it Maybe just a bad connection or switch as mentioned.  Much better than a dead short. 

 

Of course the ammeter works on all the other lights, so it is functioning. 

[chistech]

Early thirties GM cars run the positive wire from the feed source directly to the dome light. The switch feeds the ground which is usually obtained by a connection to the body metal above the door, to the switch, then to the dome light. 
it’s easy to test your wiring with a simple 12v sharp point tester. If the wire going to the switch is positive, just put the tester negative clamp to a known good ground and the tip of the tester to each side of the switch. A 12v tester will show a dim light if you have power. If you have no power, attach the tester ground clamp to positive power and then the tip to each side of the switch. If still nothing, then repeat the test at the dome light. It’s usually the ground but you said you have ground but that could still be coming through the switch. 
locate the wire under the dash running up the A pillar. On GM is the passenger side but someone posted here it’s on the drivers side on your car. Again, ground the tester clamp and puncture the wire with the tester, you should have power. Trace from there. 

[Xander Wildeisen]

You could have six dome lights for $20.00 dollars. And you can use them in a car.