Fitting a 12 volt conversion kit

This article is going to show how I fitted a GMC 12 volt alternator conversion kit to my 6 volt 1943 1 ½ ton Chevy.  It should only be used for information purposes and not as a replacement for any instructions you receive with any similar kit you may buy.  Neither MVWF nor myself will be held responsible for any damage or injury if you do not follow the original manufactures instructions when fitting a kit for yourself.

The kit I am fitting is the GMC alternator conversion kit from Jolley Engineering.  Below is the kit with all its included parts.

First of all I removed the old Dynamo and wiring.  The original adjuster arm is reused, so I left this in place. 

Next I fitted the new alternator bracket in place of the old dynamo bracket.

As I removed the alternator from its bracket in order to fit it, I have now refitted the alternator to its bracket.

Next I looped the new belt onto the crankshaft pulley, water pump pulley and the alternator pulley.  I also fitted the supplied extension bracket for the adjuster arm, as the original was too short to allow me to tension the belt.

At this point I found the first differences between the GMC and Chevy engines and alternator fittings.  The alternator was set about ¼” too far back on the supplied bracket, so the belt didn’t run inline.  To solve this I tapped the bush on the rear of the alternator out and fitted one of the supplied spacers at the front of the alternator after grinding it down to size. 

The other problem I came up against was in order to tension the belt correctly the alternator had to be pulled a lot further away from the engine than the adjuster brackets would allow.  To solve this I have manufactured a new bracket, which has a curved section to allow it to run over the contour of the alternator and allow me adjust the belt tension correctly.

With alternator now fitted to the engine, it was time to start on the electrical side of the kit.  I connected the supplied main cable to the back of the alternator.  The wires were supplied with crimped ends already fitted, so I fitted the two yellow connectors onto the two large terminals on the back of the alternator.

I then fed the wires through the bulkhead and connected the two ring terminals to negative side of the ammeter.  This is the side connected to the ignition switch, not the side that attached to the starter switch.

Next I had to fit the warning light.  This is required, as without it the alternator will not turn on its charging circuit when the engine is started.  I have chosen not to drill any holes in my dash to fit the light, but instead I have made a bracket to fit onto the side of the steering column.

I connected the blue connector to the small terminal on the back of the alternator and fed it through the bulkhead before reconnecting it to the warning light.

Then I connected the ring terminal to the ignition side of the ignition switch.  Not the battery side.

That’s it kit fitted.  I estimate that without all the extras I had to do in order to make the kit fit my engine, it should take a mechanically competent person less than an hour to fit.

As I now have a 12 volt charging system fitted there are few other things on the truck that require changing in order for them to work properly.  First of all I had to fit a resistor between the fuel gauge and sender.  This reduces the voltage flowing to the 6 volt sender unit.  I had to fit a new 12 volt ignition coil to the engine.  Then all the light bulbs/units had to be changed for 12 volt bulbs/units.