Dome light wiring

[Martin Michaels]

Good day to all, I am trying to get my dome light on my 1947 sedan to work. I have gone over the wiring diagrams in my shop manual bit there is no reference to a dome light.Mice at some time chewed thru some wires under the headliner.The lamp used is a 6 volt #88 double contact single fillement. There are switches at all 4 doors and a slide switch on the B pillar. My biggest question is what is the last switch in line that would feed the light.I thank you for any help I  receive. I purchased a a great dome light from fellow member Joe Cutler, Thanks Joe.       Marty   

[Don Boshara #594]

Marty, I believe your dome light is fed by one wire that is always hot (+), and the other wire goes to the pillar switch and the door switches and then to ground (â€").

[dplotkin]

That is mostly right, I think, except that it does not go to ground. If it is a double contact bulb, one side is hot (+) and the other goes to each door switch & to the b pillar slide switch. Any one of these switches grounds the switch leg when activated and completing the circuit.

Dan

[R Schroeder]

This could be wired to different ways.
Switch to ground , or blub to ground.
As mentioned it probably is switch to ground. There still would have to be two wires , either for the hot , or two for the ground, depending on the wiring.

See diagrams.
In the bottom diagram, the other switch is the pillar switch. Forgot to write that in.
Roy

[Jay Friedman]

If the '47 is wired like a '49 (which I'm familiar with), as previous posters said, one wire going to the bulb is always hot and its current goes into one of the contacts on the bulb.  The current then goes through the filament and out the 2nd contact and into a wire going to the switch.  The lamp and the bulb are NOT grounded.  The switch is grounded through the 2 screws that hold it to the body.  When the switch is turned on, grounding occurs, the circuit is completed and the bulb lights.   

[R Schroeder]

That's what I thought. Switches are going to ground. If that is the case, then I would be making sure that the ground screw has a very clean surface . Rust could prevent it from lighting.
Roy

[Don Boshara #594]

Isn't that what I said in the first place? Thanks for the confirmation.

[dplotkin]

Now that I re-read your post, yes, it is what you said. Any of the switches ground the other leg (contact) of the bulb.

Dan

[kkarrer]

Dan,
    That's a double "yes " about the grounding of those switches.  The ones on my 41 are the same.  After we completed the interior my dome light quit working.  I'd assumed that we'd disturbed the + (feed) or the bulb, but actually we had some material and new paint that had gotten between the switch plate, screws, and ground on the post (B pillar).  Like a friend of mine often says, "check the gound first."  Got that fixed, but I'm still struggling with getting my turn indicator/flasher to work.
Ken Karrer 6227D coupe

[Martin Michaels]

Hello, after further checking and reading all the posts the door switches are grounded with one wire going to them they are a normally closed switch. open the door circuit is complete,close door circuit is broken. pillar switch is open/closed here is a crude drawing of circuit. now to find a mazda 88 bulb no one around here sells them,probably ebay Marty

[49caddyman]

I recently went through a similar situation when trying to get the dome light (courtesy light) to work properly on a '49 Cad. convertible I've been working on for another CLC member.  At first I was a bit baffled, as the car has a new wiring harness, & there's a wire that's always "hot" which has a round, push-on connector at the end, leading one to believe it goes to the single post on the switch, which is identical to the one used on a conventional domelight.  After a little experimentation, I discovered that this "hot" wire actually feeds the courtesy light.  A 2nd wire runs from under one of the screw heads that attach the courtesy light fixture to the pocket that's routered into the rear oak bow.  Of course, being made of wood, this 2nd wire is essential to complete the ground.  This 2nd wire then runs to the single terminal on the switch, which is in turn grounded.
   I believe I have some #88 bulbs, Marty.  I never thought of providing one with the domelight assembly you bought from me recently.  If you still need one, email me at  49caddymanemail addresses not permitted   Joe Cutler

[Martin Michaels]

Thanks for the offer JoeI went to the oldest parts store in my area they had them in stock for 70 cents each a lot better than the 10 dollars I found on the net. I have both passenger doors working still looking for the problem on driver doors and pillar switch. Marty

[R Schroeder]

Marty,
Had to change your drawing a bit.
Yellow wires should be removed from drawing. Red one added.

You can check the wire at the door pillar real easy. Remove from switch and just ground the wire to the car body. It should light up the light. If it doesn't then you have a bad wire. If it does then the switch is bad.

Switch can be checked with an ohm meter. Probably can be taken apart to clean contacts too.
Roy

[Jay Friedman]

Besides an ohm meter, the switch can be tested with a continuity test light (containing a battery and that lights up when it detects a complete circuit). 

I have taken apart this type of switch several times for cleaning.  You carefully pry open the little tabs that hold it together, clean the contacts inside, put it back together and bend the tabs back in place.

[Glen]

neater layout

[Martin Michaels]

Thanks all, Passenger doors are now working, the drivers side and pillar switch still not working.I believe a mouse must have had a wire for dinner one night.The switches all checked out, I dont want to pull head liner down. I wonder if I can jump a wire to a switch and see if it will work. Marty