Dome light wiper switch wiring problem/issue?

2

206tee

Junior Member
Greetings FordBarn members,

A little background first...

I recently acquired a '30 Standard Coupe. The previous owner had installed an alternator on the car and had put in electric wipers on the car. The PO mentioned that when he put in the wiper motor, he had installed a 'kill' switch to prevent the battery from draining. So when starting the wipers, you need to turn off the kill switch, then turn on the wipers. To turn off, you stop the wiper motor, then turn on the kill switch.

OK, now here is my question/issue. I just went to install a dome light and using the instructions on page 468 of the Model A service guide for coupes, I grounded the switch to one of the body bolts above the drivers door and ran the power wire to the terminal box. Prior to connecting the power wire, I just touched the wire to the terminal and received a spark. I then turned the dome light switch to the 'off' position and touched the power wire to the terminal again and received a spark. It did not matter what side of the terminal block I touched, it would spark when the dome light switch is in the on or off position. I did not connect the dome light switch up at this time and I am not sure if I have some sort of electrical issue. Is there a reason that the dome light switch should be drawing power when turned off?

Based on my experience above, I believe that the wiper switch that was installed had the 'kill' switch installed to prevent a constant drain on the battery. Has anyone encountered this problem? If so, what can I do to get both of these problems sorted out?

Many thanks.

Tony
 
where is the cut off switch located? Make sure all the wire connections, battery terminal etc are clean and bright and tight!
 
You may have the socket for the dome light grounded, in which case the light will always be on since the body is grounded, rather than the light switch grounding it. Did you mount the socket to wood? If so, do the screw go through and touch metal?
 
Hi and thanks for the speedy replies!

1. The wiper cut off switch is a toggle switch that is located on a support brace where the kick panels are located. I haven't traced the wiring, but I am assuming its a standard off/on switch that he wired between the wiper motor and the terminal block. All the battery connections are clean and tight.

2. The dome light/switch is a all in one unit that is mounted in a block of wood between the wood roof ribs. None of the screws that hold the block in place are touching the dome light fixture itself. I have run a ground to the body bolt above the driver door. Should I wire this differently then what I am doing now? The wiring schematic I have from the Model A service manual shows that I should ground the dome light to the body and run a wire to the terminal block. Should I reverse the wiring on the dome light switch?

The good thing about this is that aside from having a bench seat, there is no interior at all. I have free and clear access to everything.

Any other ideas? Thanks again.

Tony
 
Timothy Kelly said:
The dome light switch need not be grounded. The dome light itself, other than the hot wire and contact point in the socket, should be grounded.

The hot wire should run from either terminal box stud (one is before the amp meter, the other is after) to one side of the dome light switch. The other side of the switch should have a wire running to the contact point in the dome light. When the switch is moved to the on position the circuit is complete with the hot running from the terminal box to the center contact on the bulb, and the socket on the bulb is grounded by virture of the dome light body being grounded.

You state that you grounded the switch. How did you do so? It's OK to ground the switch body, but there is no need to do so. Further, it's not OK to ground either wire to or from the switch.

Please check your wiring, and make changes as needed, and report your new findings.

As for the wiper, I haven't a clue as to what problem might be triggering the symptoms you state. If everything is correct, with no shorts, there is no need for a kill switch because of the wiper, and there is no need to sequence how the kill switch is turned on and off in connection with running the wiper.
Click to expand...

Hi Tim,

Thanks! The dome light switch itself had 2 locations to install wire, the hot wire and a second wire (Ground I assume?). I can remove the wire I am using as the ground and see if I am generating any sparks on the terminal blocks when the switch is on and off.

I'll also check the wiring on the wiper switch as well. The PO stated that he did this to prevent the battery discharging. I'll trace this circuit as well and see what I find. Thanks for helping.

Tony
 
I've never seen a dome light with two lugs. Original lamps had a screw in the shell for the ground wire if I recall correctly. There should be a single contact in the center of the bulb socket. You will need to check for continuity to know for sure that one of the wire lugs grounds to the housing (without the bulb in) or if for some strange reason they both lugs connect to the center bulb contact.

The bulb itself doesn't care which direction it's wired. However if one of those lugs is for ground and has continuity to the lamp shell AND the shell contacts chicken wire above it, the car WILL care which is which.
 
Question since an alternator is installed, is it 12V or 6V and posative or negative ground? Since you have an alternator, remember if you have either a single wire or multiple wire, the alternator field draws current when the engine is turned off. This could be the reason for the kill switch. The ignition switch on a Model A only breaks the connection from the coil to the points, everything else on the Model A is hot all the time unless you pull the fuse if you have a fuse, throw the kill switch which yours seems to have or disconnect the battery. Really confusing about the wiper wiring in this also. Follow Marco's post above and check the connections to the light to see if there is a remote possibility that the dome light itself has a short. If the dome light does not have a short, then make the wiring to everything is as close to original as possible.














terminals and there are no other connections
 
When you said you had one of the switch contacts grounded I thought you were doing your own custom dome light wiring and using the switch to ground the light, and running a full time hot wire to the lamp.

Follow Timothy's and Marco's advice and wire the dome lamp the correct way, as they have mentioned.
 
Hi guys,

Thanks for all the help! Since I last posted, I went and tried a couple of things...

1. I disconnected the ground wire and when touching the power wire to the term. box, I still get a spark when the dome light switch is turned on or off. This time though, the dome light itself would not light up. When I re-connected the the ground wire, I was able to get the dome light to come on. The only problem is that the power wire sparks when the dome light switch is off.

2. I confirmed that the wiper motor is wired with a basic on/off toggle switch. I pulled the power wire for the wiper motor off of the term. box, turned off the kill switch and I did not see any spark/power draw when touching the power wire to term. box. I am assuming that I can either keep the switch off or remove it entirely.

To answer some of the other questions that were asked...

The car is 6 volt positive ground and the alternator is a multi-wire type unit.

The dome light itself was purchased from Snyder's. It is a single contact bulb that has two screw-down lugs in the back of the bulb housing. I assumed that one lug was for power and the other for ground. The dome lamp was installed in a wood block. I will also check to see if the chicken wire may be touching the housing. It that doesn't correct the problem, I'll change the positions of the wires on the dome light switch itself to see if that makes a difference. I'll post my results. That's all for now

Thanks again,

Tony
 
Problem Solved!

It turns out that the metal dome light housing was touching the chicken wire in the roof. I put a piece of thick rubber between the dome light housing and the chicken wire and there is no more power draw when touching the power wire to the terminal box. Thanks everyone for all of the help/suggestions.

Tony
 
Sounds like the light is wired wrong. The body of the light should be the same polarity as the body of the car.

Bob
 
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