Jon, Parallel resistors (which is what a shunt is) reduces the current flow thru a circuit. If the ammeter has a certain resistance and the shunt has the same resistance, then current flow thru each would be 1/2 of the total. Adding another shunt of the same resistance as the ammeter and original shunt would divide the current flow thru each element by 3, or 1/3 of the total. Theoretically, you could get it spot on, but why bother? Again, the original ammeter is a pretty rough indicator (your yardstick measurement to Mars.
) If your truck hasn't burnt down yet, I don't think it will in the future.
