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meter data which it places on the private data bus. The tachometer receives the data
and converts it into pointer drive signals. Connections are shown in Figure 3-7.
The signal for the ammeter begins at a sense wire coiled up in the battery box (be-
tween the battery's positive terminal and the megafuse leading to the alternator). As
current from the vehicle's charging system flows through the sense wire, a voltage of
a few millivolts is generated. This voltage is applied to the Interface Module which
converts it into ammeter messages on the private data bus.
If the system is charging, the positive voltage at the sense wire causes the ammeter to
read in the positive ( + ) area. If the system is discharging, the sense wire voltage
goes negative and causes the ammeter to read in the negative ( – ) area. See Figure 3-8
for the actual wire connections.
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