Ignition Switch Circuit Question - Alternator vs Generator and System Grounding

[Jeremykentsmith]

I have a 1930 Ford Model A coupe. I recently rewired it per the pictorial diagram found in this forum. The diagram shows a generator with a wire going to one side of the junction box and then to one side of the amperemeter. Sine the generator has been updated to an 12 volt alternator, does the one wire hooked to the spade clip off the alternator tie in to where the generator tied in? Also, the pictorial diagram shows a positive ground. Mine is currently negatively grounded. Any help would be appreciated.

 

[Badpuppy]

Most important is turn the battery around from the drawing, also ammeter and coil connections. If it is a one-wire alternator, then yes it connects like a generator. If it's a standard 3-wire alt. you need to modify the ignition circuit.

Of course coil, lights, horn, starter need to be modified for 12V.

 

[rotorwrench]

A one wire powermaster only has the one terminal on the fake cut out but it also requires a ground wire to engine or frame per instructions. A regular Delco 10si 12-volt alternator just connects to the single terminal stud. They ground through the mounting to the engine. The excited terminals are generally blocked by a special plug. Those terminals are for a warning light function if so equipped.

Polarity switching affects the battery and the ignition coil unless there is a modern radio installed. An OEM 1.5 Ohm coil can be used on 12-volts but it will need a ballast resistor of 1.3 to 1.5 Ohms. The Horn should have the field coils rewound for 12-volt an of course all the light bulbs will need changing.

The starter can have new field coils installed for 12-volt but it will function on 12-volts. It will turn faster and be unkind to the old type bendix but it will function.

 

[nkaminar]

In the original wiring diagram the coil is always hot and the ignition switch connects the opposite side to the distributor. If you are using an aftermarket ignition switch it is safer to have the switch power the coil and have the other side permanently connected to the distributor. Wired this way, when the ignition is off there is no power to the coil. The ignition switch wired this way can also be used to power accessories such as your GPS so that the accessories are off when the ignition switch is off.

If your battery is negative ground reverse the battery in the diagram, as others have noted.

The horn can be rewired for 12 volts or a resistor added to drop the voltage to 6 volts. The vendors sell these resistors. Use the heavy duty one that is mounted on the frame and not the one installed in the horn housing that can get hot and burn up. See https://www.snydersantiqueauto.com/product.htm?pid=976687&cat=41718

The starter can be rewired to work on 12 volts. Field windings for 12 volt starters are available from the vendors or you can change the wiring on the existing windings. The 6 volt field windings are 2 in series and 2 in parallel and the 12 volt field windings are all in series. You will need a good trigger type soldering iron and some specialized tools to take the field winding poles out. Search the forum for information on removing the poles.

The electric windshield wiper can use a dropping resistor or a variable voltage dropping rheostat. That will convert the windshield wiper to variable speed! On my car I made a bracket to mount the variable voltage supply up by the windshield wiper. It loops over the trim there so no holes drilled. One option here: https://www.justkampers.com.au/cata...p-vw-t2-split-1950-1966-and-beetle-1946-1967/

The polarity on the coil must be correct. To test use the polarity tester available from the vendors, see https://www.snydersantiqueauto.com/searchm.htm?type=merged&sterm=&searcht=coil+polarity+tester