The ammeter is supposed to indicate power going to/from the battery so you can tell if you are charging or discharging it. For that to work, you have to have the battery on one side and everything else on the other side of it.
In some vehicles, the starter is an exception to that. It is the highest draw item in the vehicle and can be bypassing the ammeter. You would have to check the factory wiring diagram to see how your should be wired. From the factory a '51 Chevy 3100 (what I think JW51 is wiring) the only electrical devices that do not go through the ammeter are the horn and the starter. I can't remember any car/truck that had the starter on the opposite side of the ammeter from the battery. If done that way, the ammeter would have to be able to handle many hundreds of amps.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
| 
