Driver Controls and Instruments The voltmeter will normally show approximately 13.7 to 14.1 volts when the engine is running. The voltage of a fully charged battery is 12.7 to 12.8 volts when the en- gine is stopped. A completely discharged battery will produce only about 12.0 volts. The voltmeter will indi- cate lower voltage as the vehicle is being started or when electrical devices in the vehicle are being used. Primary and Secondary Air Pressure Gauges These air pressure gauges (see Fig. 3.20 ) register the constant pressure in the primary and secondary air sys- tems. Normal pressure, with the engine running, is 95 to 125 psi (655 to 862 kPa) in both systems.
A low-air- pressure warning light and buzzer, connected to both the primary and secondary systems, activate when air pressure in either system drops below a minimum pres- sure of 62 to 68 psi (427 to 469 kPa). When the engine is started, the warning light and buzzer remain on until air pressure in both systems exceeds minimum pres- sure. An air pressure gauge that registers pressure in both the primary and secondary systems may be in- stalled on some vehicles. If the voltmeter shows an undercharged or overcharged condition for an extended period, have the charging system and batteries checked at a repair facility.
On a vehicle equipped with a battery isolator system, the voltmeter measures the average voltage of all the batteries when the engine is running. When the engine is stopped, the voltmeter shows only the gel cell battery voltage and does not indicate the voltage of the engine- starting batteries. Fuel Gauge CAUTION Gel cell batteries can be damaged if the battery voltage is allowed to drop below 12.0 volts or if the charging voltage is more than 14.1 volts. Start the engine to recharge the gel cell before the battery becomes fully discharged.
If an external charger is needed, disconnect the gel cell battery and use only an external battery charger that has been approved for gel cell batteries. The fuel gauge (see Fig. 3.21 ) indicates the amount of fuel in the fuel tank(s). Intake-Air Restriction Indicator An intake-air restriction indicator measures the vacuum on the engine side of the air cleaner at the air cleaner outlet. If the yellow signal stays locked at or above the values shown in Table 3.3 , after the engine is shut down, service the air cleaner, then reset the indicator by pressing the reset button. 3.15