COOLER 1G8480 - Caterpillar

Small hole in brass button.The housing of this single terminal switch completes the indicator circuit, back to the negative terminal of the battery (via the machine frame). If this electrical circuit is interrupted, the indicator will never come on.
Troubleshooting
This procedure also applies to 7N4350 Vacuum Switch which is a the same as a 7N4351 Vacuum Switch, only it has normally closed contacts.... Indicator comes on prematurely
Factory paint may be plugging the vent hole in the switch and causing a high failure rate at predelivery. The problem is corrected when a new switch, which is not painted, is installed.
If you suspect an incorrect air filter warning, clean off (scrape) the button so that the vent hole is visible. See illustration. Then use a piece of 0.25 mm (.010") diameter wire and insert it approximately 3 mm (1/8") deep into the vent hole.
... Indicator never comes on
Use a continuity light or 6V7070 Multimeter to make sure there is a good ground connection (less than approximately 2 to 3 Ohms) from the switch housing through the 8N2242 Vibration Isolator and the air induction piping to the machine frame. DO NOT use thread sealant or Teflon® tape on the threads of the switch. The O-rings in the induction piping sometimes insulate the switch electrically from machine frame. In these situations, add a ground wire from the switch side of the isolator to the machine frame.
If a screwdriver is used to short the sensing wire to the switch housing, the dash indicator should turn on to verify the entire electrical circuit except the function of the switch.
Alternate Method Of Monitoring Air Filter Condition
If desired, install a mechanical indicator to monitor filter condition. Use a 1W613 Air Filter Indicator and the appropriate 1/8" pipe fittings to install the indicator in a vertical position. If this indicator is installed, make sure that the sensing lead from the vacuum switch is taped (insulated) so it can not short to the machine frame and turn the dash indicator on.