I got a used generator for my 26. All looked ok and had a reputable shop double check it. They confirmed all was good. Put a new diode cutout on it to be safe. When I put it on the car the ammeter showed no charge. I jumped the terminals and it acted like I grounded it out. Ammeter showed massive discharge. I just don't know where to start to trouble shoot.
A good place to start is page 249 of the service book. Chapter XXVI, "Tracing Trouble In The Generator".
is probably good at fixing "modern" generators, but most likely have no idea how to fix a Model T generator.
If you do not wish to send it away to one of our experienced Forum posters who specialize in these devices, and if there is not a knowledgeable T person near you, Dan's words are the best way to go.
"Reputable" shop should at least be capable of verifying armature condition. Read pp 3-15 of the MTFCA Electrical System book before you go and take that book with you to walk them through the procedures if need be. This video by Mike Bender, et. al., is also an excellent guide to model T generator function and repair. (Your problems could be as simple as dirty brushes and fried diode, but it all needs checking out.)good luck, jb
If the battery is backward, or if the diode was made for a positive ground, you will have a massive ground because the diode will allow current to flow in one direction but not in the other.
The battery on a Model T should be negative ground and the diode should allow the current to flow from the generator toward the battery but block the current from flowing from the battery toward the generator.
So before you spend a lot of money getting the generator "fixed" check those two items first and correct if necessary, then check the generator again.
I think all was correct when he first put the generator on since if the diode was backwards it would have shown the heavy current at that time but when he saw no charge he JUMPERED the diode and that have then applied the battery directly to a non spinning generator and that would cause large discharge as he witnessed since the armature resistance is less than 1 ohm. I think if he didn't hold the wire in place on the generator then probably no harm happened but he needs to learn how to adjust the 3rd brush on the generator since it is probable that the third brush is not set where it should be. First verify that turning on the headlights with engine stopped will in fact show a discharge on the ammeter in the 8-12 amp range since if the ammeter is not accurate then the 3rd brush won't be set accurate either.