1949 Ford if everything is stock was 6volt positive ground system, if memory serves me right. The sol. is seperate from the starter and usually is mounted to the inside fender well on the starter side of the engine.
My best guess is that you have a dead spot on the commutator and the bars are shorted--- That is if the battery cable is getting warm or hot. Usually meand a short/ground between the bars on same.
Quik fix : Sometimes you can rap the started body with a hammer a couple of times and the brushes will hop over the bad spot and then it will wind up, turn over and start for you. The only other problem could be that the air gap between the sol. contactor that sets the bendix drive is to great or has an onion skin burnt onto it and won't index the bendix drive gear. But usually with that condition the starter motor will just sit and spin freely without engaging....
I suspect a bad commutator!!! Did I mention it is a commutator problem???