Not really sure whats going on. Yesterday the starter worked fine for my first fire on my new 1949 chevy 3100 swb. All original besides being coverted to 12 volts ( no telling how long its been off the road but has some new parts on it). Then all the sudden it just stop doing anything but i could hear some clicking when pushing the button from under the hood. Today i took it off and bench tested it and it ran fine... put it back in the truck and hit the pedal and it tried to turn flywheel and then just stopped doing anything again but the clicking. Any ideas? Any help would be greatly appreciated. Really looking forward to getting this old truck fired up.

1964 impala ss
1949 chevy 3100