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222 Build Your Own Electric VehicleFi g u r e 9-12 Auxiliary relays—120-volt A C (left) and 12-volt DC (right).Fi g u r e 9-13 Terminal strip.ShuntsShunts are precisely calibrated resistors that enable current flow in a circuit to bedetermined by measuring the voltage drop across them. Two varieties are shown inFigure 9-14: the left measures currents from 0 to 50 amps; the right measures currentsfrom 0 to 500 amps.AmmeterThe most useful of all your EV on-board instruments is your ammeter. The dual-scalemodel shown in Figure 9-15 (top left) delivers 0- to 50-amp or 0- to 500-amp monitoringranges at the flip of a switch. The higher range enables you to determine your motor’sinstantaneous current draw; it functions much like a vacuum gauge in an internalcombustion engine vehicle—the less current, the higher the range, and so on. The lowerrange functions the same as the ammeter that might already be on the instrument clusterof your internal combustion conversion vehicle—it tells you the amount of current your12-volt accessories are consuming.Fi g u r e 9-14 Ammeter cur rent shunts—50 amp (left) and 500 amp (right).