Another generator question - A new one on me!

[Marshall V. Daut]

After finally getting the engine to run in a friend's newly-purchased '26 T, it was noted that the ammeter did not register a charge even when the engine was revved up. The ammeter was wired backwards (of course!), showing a charge when the lights were tested. Once the ammeter wires were corrected, turning on the headlights gave a discharge on the ammeter. So, we know the ammeter works on both sides of zero.
Before polarizing the generator, I thought it best to remove the cutout to see if it could possibly be an electronic model, which is not supposed to be jumpered. Thank goodness I did that - it is an expensive electronic cutout for negative systems. 'Dodged the bullet there! I will assume it's good, as it appears brand-new.
Removing the generator to test it with a battery, it "motored", maybe not as fast as I would like, but it did spin. That's a plus = the armature isn't burned out. The cover band was removed and I was greeted by an additional two-wire affair with a fuse, which I had never seen. The fuse filament does not appear to be broken. Look at the photos. What is this for? I am reluctant to adjust the third brush holder to increase the charging rate because what if this wiring addition is some kind of regulator or surge protector and by me attempting to increase the charging rate, I screw something up? I know I need to clean the armature plates, but if they were really terrible, the generator wouldn't even motor.
Should I loosen the third brush plate via the nut (see arrow) and move the holder to increase the charging rate? If not, why does the generator motor, but not put out a charge?
Marshall[image][/image]

[Moxie26]

Marshall.. that generator could be a Patterson rebuild, as he did put a fuse in like that. I would suggest getting a flathead wood clothespin, cut a strip of 320 sandpaper and apply that to the clothespin head. Start the car and apply the 320 sandpaper to clean up those contacts. You should get the positive reading on your ammeter. Some people have even used brake cleaner spray with the straw attached to clean contacts in the running mode.

[AndreFordT]

The fuse should be between the field wire and the third brush.
Why the fuse:
By a broken connection to the battery, the generator will build up his output well over 20V. ( tried it with a volt meter over a test light between the generator post and its house. At 28V the light burned out)
Also the current in the field will go up. The fuse will burn and the generator will be safe.

Andre
Belgium

[speedytinc]

A generator that wont motor wonr work.
A generator that will motor might work.

I would put back on the motor. Run & clean the commutator with fine sand paper.
Make sure the brushes all move freely & are contacting the commuter.
Take an analog voltage reading @ the output terminal. 0 volts = dead. 7.5V + good.
Start with increasing the 3rd brush.(move toward motor) If you get a good voltage reading or ammeter reading, great.
If not.....
Follow the in car generator adjustment from the service manual.
Still no joy? - rebuild time.

[Marshall V. Daut]

I will follow the suggestions given so far, now that I know the in-line fuse is just a protection against burning up the generator. Thank you, all.

Looking for other possible causes of the charge not reaching the ammeter, I studied the HUGE wiring diagram by Patsy Winn, tracing from the generator to the firewall terminal block and hence to the ammeter. When I swapped wires around on the ammeter to get the correct orientation, I noticed that the short wire on the diagram running from "Batt." on the switch to the "+" side ammeter terminal is missing (see yellow arrow on attachment). Granted, the diagram is for a 1919 to 1925 Model T with starter, but unless this wire was dropped in 1926, shouldn't it be there, connecting the switch to the ammeter? That would make TWO wires on the positive ammeter post, not counting the dash light, which is also missing from this car. I am wondering if perhaps the lack of this wire might explain why the charge from the generator isn't making it to the ammeter. Yet, in the wiring diagram in MTFCA's Electrical Booklet, this short wire is present, but the longer wire from the "Batt." terminal strip does NOT run up to the ammeter, meaning the "+" ammeter terminal has only ONE wire connected to it. Which is correct for my friend's 1926 T and could the missing short connecting wire be why the generator's juice doesn't reach the ammeter? Grasping for straws here...
Marshall

[Mike Silbert]

Marshall,

For a 1926 wiring diagram I use the ones on the Texas T Parts website
https://www.texastparts.com/mm5/manuals ... iagram.pdf

The wiring to the ammeter can be done in several ways.
Some will work fine and others not so.
And some wiring diagrams and replacement ammeters have the wiring backwards so it needs to be checked carefully.
Sometimes the 2 wires are under the terminal on the switch side and not the ammeter.
While you are in there check that all connections, including the bus bar rivet, are good to prevent future problems.
If the car has a dome light or dash light there will be a 3rd wire somewhere.

The bottom line is that the battery (yellow wire) goes on one side of the ammeter.
The other side gets the generator wire (Yellow w/ black stripe), the Ignition switch wire feed wire (Yellow w/ black stripe), and any dome or dash light wires. Somewhere all these wires get connected together and it can be at the ammeter or the switch terminal marked BAT. The electrons do not care which ends of the jumper wire the generator is hooked to. It belongs on the ammeter stud because that is a taller, stronger connection with more room for stacked connections.

If the ammeter works backwards then all wires on each terminal need to be swapped like you did.
Mike

[Marshall V. Daut]

Mike -
Thanks for the explanations and 1926-27 wiring diagram. This one shows a wire going from the generator screw in the terminal block to the horn button. Doesn't it usually come from the "Batt." screw in the terminal strip? It seems that no two Model T wiring diagrams agree on all points.

O.K. Given that this Texas T Parts diagram also shows that short connecting wire from the switch to the ammeter, what would be the symptoms if that wire were missing, as in my friend's Model T? That wire must be there for some reason! Everything else electrical seems to work = ignition (on battery and on magneto), headlights, and taillight. The only thing left non-functioning is the generator not sending juice to the ammeter. That fact and the missing connecting wire make me think there is a relationship between the two. Is there? What would happen without that short wire connection?
Marshall