buddha,
It shouldn't be a factor in this instance. I think we are talking about a '49 pickup, so it probably has a stomp starter. In regards to starting, the key only energizes the ignition, the action of the "stomp" drives in the bendix and completes the circuit from battery to starter. It is two different things..."the truck turns over, but won't start" as opposed to, "the
truck won't turn over".
If the truck won't turn over, it's because it
hasn't enough juice or it has a defective starter. Start at the beginning..get the truck to start first. Did you keep the 6v starter? Have you tried a donor battery yet?
Don't buy a new battery until you rule the old one out by testing and charging it. There is still the possibility that it could be the starter switch or the starter. We started at the battery because it is the "usual suspect". Be sure to check your cable connections. Both cables must be clean and attached firmly..very important.
Stuart