12v Converted 1929 'A'
 

Folks:
I have a converted 1929 'A' over to 12v negative ground. after doing some work on it with other 'odd' issues, I have seen thru the suppliers that they sell a coil that doesn't require the ballast resistor. I had issues when I was bringing it out of storage and had already replaced the coil as it wasn't getting spark thinking that was the issue. Turned out the ammeter was faulty.

I am trying to re-wire it back to as much stock as I can, I have installed a brand new wiring harness and it has the 12v alternator. why would I require the Ballast resistor in the loop or can I use the resistor-less coil from the suppliers.

ps.
I did NOT do the conversion to 12v so I don't even know what is involved with that conversion.

Re: 12v Converted 1929 'A'
 

Some coils have the ballast resistor built in.

Re: 12v Converted 1929 'A'
 

Measure the resistance of the primary winding of the coil, aprox 1.5 ohms would be a 6 volt coil, aprox 3 ohms would be a 12 volt coil.

Re: 12v Converted 1929 'A'
 

Use a 12 volt coil, no resistor. The only wiring differences for negative ground are polarity of ammeter and coil are reversed.

Re: 12v Converted 1929 'A'
 

does anyone here behind the barn have any sort of wiring diagram on what a properly converted Model A should be? I am trying to fix all the PO's work and want to do it right

Re: 12v Converted 1929 'A'
 

i converted my 31 pu and recent speedster to 12v. i went round and around with guys at local parts suppliers trying to get a 12 v coil with built in resistor, if you can't tell them what year it was used on they are lost. they sold me coils for around $40.00 dollars that still required external resister for 12 v. use. finally i found the correct coil on amazon with built in resistor for a lot less money. it is sold as a coil for converting ford tractors to 12v. BINGO! that is what i was wanting and for a lot less money than the local cog house wanted for coils that wouldn work.

Re: 12v Converted 1929 'A'
 

Good intel, tnx.

Re: 12v Converted 1929 'A'
 

Use the standard wiring diagram you will find many places. Just note reversals of battery, ammeter and coil. Horn, coil and electric wipers will need to be 12 volts. All 3 6v parts can be used, with a dropping resistor of proper value for each.

Re: 12v Converted 1929 'A'
 

the reason i beat the bushes to find a coil with internal resistor is no wanting to see a resistor looking so out of place on the firewall, remember the 55 and later gm cars with the resistor on the firewall. i know they were running 6 v, coils on 12 v. in series with a resistor, but there it hung for several years.