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Topic author
Steve Jelf
- Posts: 6496
- Joined: Fri Jan 04, 2019 9:37 pm
- First Name: Steve
- Last Name: Jelf
- * REQUIRED* Type and Year of Model Ts owned: 1923 touring and a few projects
- Location: Parkerfield, Kansas
- MTFCA Number: 16175
- MTFCI Number: 14758
- Board Member Since: 2007
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Contact:
Post
by Steve Jelf » Fri Sep 30, 2022 11:45 am
From reading Model T lore you might think magneto headlamps burn out at a furious rate. But when I had a bulb go out last week that pair had been in the car for at least three years. I don't do much night driving, but I seldom shut off the lights. When the car is running the lights are on.
Mag lights being wired in series, like old time Christmas tree lights, when one dies they both go out. Being wired in series also means the bulbs must be the same kind, with the same filament, voltage, resistance, etc.
Matching bulbs light equally.
If the bulbs don't match one will be bright and the other dim.
One may be so dim that it doesn't even light.
So to be sure the spares I carry in the car are matching pairs, I made a simple tester.
It's just a switch and a pair of 1176 sockets wired in series. I had to buy the sockets online, of course.
If two bulbs light equally I can pack them as a pair.
The inevitable often happens.
1915 Runabout
1923 Touring
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Novice
- Posts: 584
- Joined: Tue Jan 08, 2019 12:25 pm
- First Name: Jim
- Last Name: Davis
- * REQUIRED* Type and Year of Model Ts owned: 1926 Touring. 1923/26 Open Express. 1920 depot hack
- Location: Tomball,Texas
- MTFCA Number: 49832
- MTFCI Number: 24686
- Board Member Since: 2017
Post
by Novice » Fri Sep 30, 2022 12:08 pm
That sure a large battery just for testing light bulbs.
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Topic author
Steve Jelf
- Posts: 6496
- Joined: Fri Jan 04, 2019 9:37 pm
- First Name: Steve
- Last Name: Jelf
- * REQUIRED* Type and Year of Model Ts owned: 1923 touring and a few projects
- Location: Parkerfield, Kansas
- MTFCA Number: 16175
- MTFCI Number: 14758
- Board Member Since: 2007
-
Contact:
Post
by Steve Jelf » Fri Sep 30, 2022 12:22 pm
That sure a large battery just for testing light bulbs.
It comes in handy for running the car. 
The inevitable often happens.
1915 Runabout
1923 Touring
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Colin Mavins
- Posts: 312
- Joined: Sun Jan 06, 2019 1:36 pm
- First Name: Colin
- Last Name: Mavins
- Location: Winnipeg Canada
Post
by Colin Mavins » Sun Oct 02, 2022 11:13 am
Dad put the mag lights back in the 12 in 1967 and not used much in the past 50 years or so we have never replaced a bulb. When I need them they always light. Im still waiting to burn one ,and have 50 odd new ones, maybe that keeps the old ones going. This is the first time I herd about matching I'll have to look in to this Cheers Colin
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Altair
- Posts: 365
- Joined: Thu Jan 17, 2019 11:52 am
- First Name: David
- Last Name: Menzies
- * REQUIRED* Type and Year of Model Ts owned: 1926 Touring and 1915 Touring both Canadian models
- Location: British Columbia
- MTFCA Number: 27825
- Board Member Since: 2012
Post
by Altair » Sun Oct 02, 2022 11:23 am
The original bulbs were 9 volts, in series 18 volts resistance and the mag rarely reached that voltage at normal driving. Most bulbs today are 6 volts and pared will only attain a 12 volt resistance, still OK if you don't rev it too high. For an added safety a third 6 volt bulb can be wired in series into the circuit for a total of 18 volts resistance. The bulb can be hidden under somewhere or displayed for additional lighting purposes.
