10987 is serial number . did the early 9n tractors use a special cut out

Your 1940 would have been factory equipped with an "A" generator that uses a 3 terminal square can voltage regulator. If your generator is roughly the same diameter as the pulley and the pulley is secured with a nut you have an A generator. If your generator pulley is not secured by a nut you have a B or C generator and require a round can cutout relay.

I believe the early 9N's with the "A" generator came with a square case voltage regulator. When they revised the generator for more output for lights, the "B" generator came out with a round can cutout relay.

More info in link below,
Tyler

• THE HISTORY OF THE FORD-FERGUSON 9N TRACTOR GENERATOR