SPECIAL AR 4339981 - Caterpillar

Fuse Failure Modes
Open
An open fuse is the result of system overload. Fuses with the element visible can give a clue as to the cause. Testing on a questionable fuse only requires a 6V7070 Multimeter (or equivalent) on the 200 ohm scale. A good fuse will read less than approximately 0.2 ohms. An open fuse will read "OL" for open circuit.
1. The glass or plastic housing is smoked or blackened. This is caused by gross circuit overload far beyond the fuse rating. This is usually caused by a short circuit-to-ground from: ...Incorrect troubleshooting as with a screwdriver.
...A component short as in a forward warning horn.
...A harness short where a wire (conductor) is pinched to make a connection to ground.
2. The glass or plastic housing is clear showing the fuse element simply melted open. This is caused by a gentle overload somewhat greater than the fuse rating.Will not fit fuse holder
1. Incorrect type or size of fuse for holder.2. Supplier tolerances are incorrect.Breaker Failure Modes
Open
An open circuit breaker is an automatic or manual breaker that will not reset (reads "OL" on 6V7070 Multimeter). This usually occurs from gross circuit overload far beyond the breaker current rating. This is usually caused by a short circuit-to-ground from: ...Incorrect troubleshooting as with a screwdriver....A component short as in a forward warning horn....A harness short where a wire (conductor) is pinched to make a connection to ground.
Failure of a circuit breaker to reset is often caused by a melted disk or a disk that was so hot during overload that it is warped and cannot be reset to a closed position.
Shorted
A shorted circuit breaker, one that will not open under an overload, is rare and might be found in a circuit with wiring and/or harness damage. This may possibly be caused by an overload condition that welded the disk in place.