A short would be smokin' hot, as said. Burn thru a wire maybe. By the time you dig out all the wire looking for a broken wire, you are half way to replacement. Forget the short scenario. Re wire the truck. No fuses is a NO-NO. They omitted them back then because they didn't know anything about automobile electrical safety..... As T-Nix says: Only one fuse shown on 1939 Wiring Diagram, at headlight switch. (37-38, one fuse on back of ammeter)
There are VERY FEW wires on an old truck. You don't even need a harness sometimes. FLAPS sell 20' spools of all colors of primary wire for $7. Get a fuse panel from anywhere. Very simple. As RustyRod said, one at a time. Make "improvements"/upgrades if you want. We can help further if needed. Lots of pre-AD guys in here. Wiring is pretty much the same for all era's.
A, so called, "harness" for 1936-1939 is $230. So many different "kinds" of harnesses. If they don't have the connectors for headlights and any other places with connectors, then it's just a bunch of wire hanging off a small fuse box. Connectors are the male and female shells with contacts that snap into the shells. I.E. Ignition switch, tail light, stop switch connectors. Probably not too many, if any, used in 1939? Probbly most components are "hard wired." Just take a look, draw a diagram of all wires, and where they go, and study to see how easy it looks. If the only "connector" needed is a headlight socket, they are available for $5.
