Another Interior Light Question

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Pete Lenzini
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Another Interior Light Question

#1 Post by Pete Lenzini »

Greetings,

I have no functioning interior lights on my '64 SC coupe. I've read dozens of posts on the subject and looked at several Joe Leoni and Greg Bryan diagrams and discussions and can't find an answer. Some background: I have battery voltage at the dash light and both dome (i.e. B pillar) lights but the brown wires, which I assume are supposed to be grounds, are not continuous with ground. However, the brown wires at the dash and dome lights and driver side door switch are continuous with each other. If I put the red lead of my multimeter on the hot wire (black or black and purple) of each light on the brown wire at each light I read about 2 volts, whereas if I out the black lead directly on a body part, I read battery voltage.

My conclusion is that all of the brown wires at each of the 3 lights and the driver door switch (I didn't take the trouble to get at the passenger side switch) are continuous with each other but are not grounded. Sometimes I've see some connection between a brown wire terminal and ground or an intermittent connection but what I think the problem is is at the place where all these brown wires connect to the body, or to ground. Anybody know where such a point may be?

Another side point is that in many of the posts I saw mention of there being a tab or prong on the dome light fixture that provides ground by fitting into a notch in the metal around the hole. My '64 has a copper tab on one end and notches in the metal but that tab is not connected to the bulb terminal regardless of how the light is switched so the ground has to be the brown wire. In fact on the driver side the headliner material was between the tab and the notch.

Any help would be greatly appreciated as always,

Thanks, Pete
'64 356 SC
'14 Carrera S

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Mike Wilson
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Re: Another Interior Light Question

#2 Post by Mike Wilson »

The small tips on either end of the lights are supposed to make contact with the metal of the roof. Sometimes the headliner prevents this contact. What I have done is run secondary grounds to the lights. On one side, I drill a hole for a self-tapping screw and run a wire with a ring terminal on that end to a spade terminal on the tab on the light. I've also run a ground wire under the headliner to the other light.

Mike
Mike Wilson
Lomita, CA
'63 B coupe

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Martin Benade
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Re: Another Interior Light Question

#3 Post by Martin Benade »

Some original lights have a ground tab for a wire, or the little finger that touches dash metal. Those are only needed for the switch on the light to function. The brown wires get grounded by the door pin switches. I guess you know that the light is powered at all times and illuminated by adding a ground.
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Paul S Zuchowski
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Re: Another Interior Light Question

#4 Post by Paul S Zuchowski »

The brown wires from the dome and center lights are all connected to the door switch circuit. They are all shorted together. If either door opens, the switch at that door makes contact with ground at the door jam and the lights come on. The lights have 3 positions. Off, On and "on with door." The brown wire only comes into affect when one or more of the lights are in the "on with door" position. It is a switched ground. I have one dome light that has a third terminal. I used a short lead to a self tapper that I put into the roof support next to the light. On the other side of the car, the light fixture made contact with the metal in the roof and did not have a third terminal. If you get confused you may want to pull the fixture out of the car and figure out what is what on the bench. If you get stuck, add a picture and I can probably help.

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Pete Lenzini
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Re: Another Interior Light Question

#5 Post by Pete Lenzini »

Mike Wilson wrote: Thu Jul 28, 2022 3:34 pm The small tips on either end of the lights are supposed to make contact with the metal of the roof. Sometimes the headliner prevents this contact. What I have done is run secondary grounds to the lights. On one side, I drill a hole for a self-tapping screw and run a wire with a ring terminal on that end to a spade terminal on the tab on the light. I've also run a ground wire under the headliner to the other light.

Mike
There aren't any small tips to make contact with the roof on a '64 SC, at least not on mine. There is nothing in the light fixture that makes contact with the bulb holder on either end except the spade terminals that the hot wire and the ground wire attach to.

Thanks,
Pete
'64 356 SC
'14 Carrera S

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Pete Lenzini
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Re: Another Interior Light Question

#6 Post by Pete Lenzini »

Martin Benade wrote: Thu Jul 28, 2022 3:44 pm Some original lights have a ground tab for a wire, or the little finger that touches dash metal. Those are only needed for the switch on the light to function. The brown wires get grounded by the door pin switches. I guess you know that the light is powered at all times and illuminated by adding a ground.
Yes, I understand how the lights are always powered and are illuminated by the ground. There may be a possibility that my door pin switches aren't functioning. I should be able to easily check that by bypassing the switch itself and attaching a wire to the wire behind the switch and then ground that wire and see if the lights light. Strangely, my passenger side door switch has a nut that holds the switch in place but my driver's side just has a couple of spring-loaded strips that compress when the switch is inserted in the hole. I cleaned all these parts including around the edge of the hole with fine sandpaper and/or steel wool. I need to check the door switches more closely.
Thanks,
Pete
'64 356 SC
'14 Carrera S

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Mike Wilson
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Re: Another Interior Light Question

#7 Post by Mike Wilson »

Pete: can you post a pic of your light(s)? It'll help us with your issue.

Mike
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Martin Benade
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Re: Another Interior Light Question

#8 Post by Martin Benade »

You also have the light switches deciphered as to on, off, or door switches? I am only familiar with the dash one as I have a cab. I think your roof ones the lens rocks to on and off positions? I’ve never had a C.
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Mike Wilson
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Re: Another Interior Light Question

#9 Post by Mike Wilson »

Right, Martin, the C's have the rocker type but still have a grounding strip on the end. The dash light is like the ones on A's and B's.

Mike
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'63 B coupe

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Pete Lenzini
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Re: Another Interior Light Question

#10 Post by Pete Lenzini »

Hey Guys,

I think I know what I was doing wrong or not doing right is maybe a better way to put it. I had taken the dome lights and the dash light out and I was expecting the brown wires for the dome lights to be grounded. But they will be grounded only with the doors open or with the switch on the dash light in the right position. So I should have had the dash light in place and connected so that I could put the switch in the right position. I don't remember the details but I know at least some of the time when I was checking grounds I was sitting in the seat with the doors closed! Duh! Tomorrow I'll think a little more what I'm doing, have the doors open or closed and have the switch in the right position for what I'm trying to check.

Sorry for wasting your time but your remarks at least made me think a little more about what I was doing,
Pete
'64 356 SC
'14 Carrera S

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Martin Benade
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Re: Another Interior Light Question

#11 Post by Martin Benade »

It only needs to be installed for going on at the light,s switch. Or dangling from its wires with the pin switch grounding it, as long as the light is set to that mode.
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Mike Wilson
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Re: Another Interior Light Question

#12 Post by Mike Wilson »

No waste of time at all, Pete. It keeps us sharp, helps you diagnosing the problem and, the topic is a searchable thread for future reference. Keep us posted. By the way, the lights have three positions: on with a door open, on with doors closed and off.

Mike
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Pete Lenzini
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Re: Another Interior Light Question

#13 Post by Pete Lenzini »

Mike Wilson wrote: Thu Jul 28, 2022 8:07 pm No waste of time at all, Pete. It keeps us sharp, helps you diagnosing the problem and, the topic is a searchable thread for future reference. Keep us posted. By the way, the lights have three positions: on with a door open, on with doors closed and off.

Mike
Thanks Mike! The comments definitely helped set me straight.
'64 356 SC
'14 Carrera S

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Pete Lenzini
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Re: Another Interior Light Question

#14 Post by Pete Lenzini »

Martin Benade wrote: Thu Jul 28, 2022 8:04 pm It only needs to be installed for going on at the light,s switch. Or dangling from its wires with the pin switch grounding it, as long as the light is set to that mode.
Thanks Martin. Main problem I had was "...as long as the light is set to that mode"

Pete
'64 356 SC
'14 Carrera S

Hugo Karasawa
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Re: Another Interior Light Question

#15 Post by Hugo Karasawa »

Read Greg Bryan´s article Interior Lights / wipers. Vol 40 number 3 September / October 2016.
You can find it in Media Center Magazines
Int Light diagram.jpg
The door switches do have an aluminum nut that holds those in place.
door switch.jpg

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