Voltage at coil lights/no lights

Desert Toad

Desert Toad

Member
Greeting All!

I'm new here, looking forward to all this forum has to offer.

I have been blessed with having my grandfathers 1930 Sport Coupe passed down to me. It's been just sitting in a garage for about 10 years, so I've spent the last few months cleaning things up, so far so good! The motor runs beautifully now, but I have a question about voltage at the coil.

When the motor is running, the voltage is between 7 and 8 for the most part. When I turn the lights on, the voltage into the coil remains the same, but the voltage out increases quite a bit, as high as 10. Is this a sign my coil needs to be replaced?

Let me back up a bit and say this car has the original motor, and everything is still original 6 volt positive ground. It had a frame off restoration back in 1992. Also, the lights have been an issue. If I run with the lights on, the motor will begin to miss an run rough. It seems this is a common issue for these cars, but I'd sure like it run like Henry intended.

Sorry for the long post, but I get excited when I talk about "Frank". :)
 

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I should also add that while driving, my ammeter shows a charge until the lights are turned on, then the discharge can be as much as 10 amps.

Thanks!
 
Hmm. Voltage between 7 and 8 indicates your generator is working properly. Static voltage for the battery is like um, 6.2 and this indicates you're getting a charge (watch your battery electrolyte level if you don't have a voltage regulator/cutout.) I might disregards the voltage in/voltage out issues of the coil as you're probably getting inductance effects which your meter is showing.

The engine having issues when the lights are on indicates to me a possible short in the light wiring. This is not unusual if your lights are the original setup with the plugs/bullet ends/light conduit ferrules. The original setup NOT one of Henry's better ideas: a lot of hobbyists simply do away with the plastic keeper plug and solder the wires together with shrink tubing as proof against shorts. Also check your bulb sockets as some aftermarket made in this timeframe (80s-90s) have plastic insulators which melt rather than the red phentholic as original.

You can narrow down the headlight issues by selectively removing a segment at a time. The issue can also be in the switch at the bottom of the steering column. A lot of aftermarket switches/harnesses have flaky issues also.

Still if your engine starts and runs easily, the motive part of this seems like it is AOK?

If you tell us more likely someone will have a lightbulb moment and tell you EXACTLY what worked for them?

Thanks! Welcome to Model A Land.

Joe K
 
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