1950 Pony Wiring Problem

[gaillarry]

Runs good but the ignition switch has been giving me problems - sticking and not working.

Tractor was converted to 12 volt before I got it.

Installed a new switch (same as the old one) and it starts ok but the switch won't turn off the engine, it continues to run. Have to pull off the wire on the ignition coil (runs from the switch) to shut off the engine. Reversed the wires on the switch, same problem.

The odd thing: with the ignition switch off there's no power to the ignition coil but power when the switch is on - so the switch is working but the engine continues to run.

I'm totally baffled.

 

[rvirgil_KS]

Sounds like a 3 wire Delco alternator with a wire going direct from switch to #1 pin on alternator. When you turn swith off, alternator continues to feed back from #1 pin to coil.

Solution is to install a diode, resistor or "idiot light" between switch and alternator.

I find the easiest is to use a diode rated at least 1.5 amp @50 volts. (Radio Shack 276-1661 has nice heavy leads) Install with marking band on diode toward alternator. This will block the feed back and your engine will turn off with the switch.

 

[gaillarry]

Thanks for the reply. I like the idea of an idiot light, can you explain that more (I'm an electrical dummy) !!

 

[rvirgil_KS]

When you turn the switch on, 12 volts is applied to one side of light, other side of light goes to #1 pin on alternator and to ground through alternator causing the light to light glow.

When you start the engine, current/voltage through light turns the alternator on and alternator supplies 12 volts internally to the #1 pin. With 12 volts on each side of the light very little or no current flows and the light goes out.

Thus if the light is out it indicates the alternator is charging. If light comes on with engine running it indicates a charging system problem.

When you turn the switch off it removes power to the coil. A diode is a one-way device allowing current to start the alternator but blocking reverse current to the coil. A light limits the current to a level far less than is required to power the coil, so with no or insufficient power to the coil the engine has no spark and shuts down.

 

[gaillarry]

I went to the local autoparts store just before it closed (new years eve) and of course they had no clue about an " idiot light". What do I look for?

 

[gaillarry]

Picked up a diode at the local radio shack and problem solved !!!
Now to look for a 12v coil - get rid of the 6v and resistor.

 

[rvirgil_KS]

NAPA IC14SB or equivalent. Should be marked "12 Volt no external resistor required"