12V conversion

While I often give advise about conversions on the Ford board so I do not consider myself electrically challenged I would like to run a idea by you all to make sure I am not over looking a important detail. I do not have a gas tractor to try it on to see how it would work either.

I think we can agree that one of the main problems people have when doing a conversion on a gas motor is to get it to turn off when the key is turned off. Like you I have seen many ways of making this work. (one way diodes; trailer marker lights; horn buttons; ect) I think you have about 8 or 10 of them already and this may even be one of them.

I have been bouncing the idea around and think a automotive key switch will work. On this switch there is a acc. plug that gets power in the acc and run position and a run plug that gets power in the run and start position. The thing I am thinking though is the acc plug and the run plug are not connected in the key off position. This would allow you to hook a wire from the acc plug on the key to the P1 post on the alternator. You could then hook a wire from the run plug on the key to the + post on the coil.
When you turn the key to the run position both would get power but when you turned the key off they would be disconnected from one another to allow the engine to kill.

So what am I missing if any thing.

This seems so simple and I think it may be a good alternative for the electrically challenged person. With a diode you have to make sure you get the correct size and install it facing the right way. With a marker light you got to mount it some where and finding one that has 2 wires and is not grounded through the case can sometimes be a pain. And I am sorry but a horn button just looks out of place on these old tractors plus you got to remember to push it on every start up.

Thanks John

The popular and commonly use 3-wire Delco 10-SI alternator requires a "switched excite" volts applied to P-1 terminal. The seperate ACC terminal of a NEW ignition switch works wonderfully for this. And the seperation of volts prevents the alternator guttz from backfeeding volts to the ignition coil and continue running the ignition coil preventing the engine from turning OFF.

The biggest problem with this scheme is the electrically challenged converter don't wanna spend "the bucks" for a NEW IGNITION SWITCH. You doubt they're cheap? Look at the use of a $2 12-6v converting resistor for the 6v ignition coil instead of buying and installing a real 12v $30 ignition coil with hotter sparkies.

GM accomplishes the same effect of 2-stones with 1-bird by running their switched volts thru an idiot-lite to P-1. The idiot-lite reduces the backfeed volts so the coil volts ain't strong enuff to run the sparkie coil. (Ohms Law and Kirchhoffs Law still rule) And GM saves money on not installing an ampmeter for idiot drivers to ignore. They could use their ACC terminal but that would be too simple..... ...Dell

I was thinking this would work just wanted to make sure I was not missing some small detail before I recommended it to some one else.

I think I will start using this method on all 12v conversion questions other than the x01 series which has a idiot light in the dash. Like some one else said..... Simple is usually more reliable.

See when you do a conversion you need to hook power to the P1 post on the alternator to get it to start charging. You also need to hook a hot wire to the coil to make it fire.

The problem is both are hooked to the run side of the key and when you turn the key off the alternator will back feed power through this common connection to the coil.

By separating the wires you stop this back feed. Lots use a horn button in the alternator wire or a idiot light or a one way diode that only allows power to flow in one way.

I think this 2 post auto key will solve that problem also.

While you could hook it up to start with the key you would need to change the relay to a auto type.

This set up will still use the starter button on the trans.