Ok so it’s my first go round with a flathead. I just bought the car and was told the 1946 59A motor was converted to 12v, negative ground. It has a 12v battery, 12v powergen and attached photos of distributor/coil. The confusion started when I hooked up an electric tach and it would not work, shows no needle movement. I tried 2 tachs also… After tracing wires I found 12v ign power to the - side of the coil and + side of the coil goes to the capacitor. Is this correct? I thought it was the other way around and the tach signal was off the - side of the coil… thanks!
You said it's an electronic tach. Are you sure there aren't three wires? Was the coil upgraded to a 12v coil? I don't know of any of my friends who run a tach on their 59A so I can't ask them about it. Try to find a mechanical tach that runs from the distributor, cam or crank. This is what was used in flatheads back in the day.
Tach wires? There are 4. Red to 12v power White lights power Green to - coil Black to ground I have good ground, 12v at red wire, 12v at green from coil. Tach light comes on with headlights. looks like a 12v coil. Car runs fine…
Possibly someone forgot about the coil when going from positive to negative earth? I'd want to follow the + and - markings on the coil, unless I had a good reason not to.
Right now the - coil is hooked to 12v ign power and + is down to the capacitor on the dizzy. Should I swap the wires on the coil? Everything else on the car (gauges, starter, generator, battery) is all 12v negative ground.
Yes mechanical tach an electronic one changes the signal in the ignition system . I have yet to scope how it effects the signal but it's just all bad apples so my installs and everyone I know running stock factory ignition runs mechanical tach . Have fun it's neat stuff especially finding all components take your time as it comes is as it comes . I'm looking also and I believe in vintage parts !
And as a bonus, I believe you will have a slightly better spark too. The electrons have an easier time jumping from the hot center electrode to the colder ground electrode on the spark plug, not a huge difference but everything counts.
You still need to check the coil. The polarity of the coil must be correct to the polarity of the car. It may run ok now but a DC spark has one side of the spark run hotter than the other so could give reliability issues with the points and plugs in the long term
You speak the truth, I converted my ‘42 Ford PU to 12v negative ground. Not really thinking about it when I installed the ballast resistor and another coil I had, I searched for “42 Ford PU ignition wiring” and promptly hooked it up backwards. It did have spark, but only jumped maybe an 1/8th to 3/16ths of an inch. Buddy came by and spotted it immediately.
Great ! The old swap the wire trick ! Whew! Glad it worked out . It was good advice and on newer cars could have compromised other components and affected other systems
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