Battery disconnect switches, aka “kill switches,” discourage machinery theft and reduce problems with batteries being drawn down during storage.
There are two approaches to installing a battery disconnect. Electrical experts say either way is valid, and point out advantages/disadvantages to each approach.
Install the disconnect switch on the positive battery cable: Construction equipment and over-the-road trucks often use this design. A concern with positive-side kill switches is the same as when connecting/disconnecting battery jumper cables: there is the potential for sparking if the positive cable is interrupted while the negative cable is connected. Heavy-duty quick-throw switches are designed to handle that issue.
Install the disconnect switch on the negative battery cable: Installing the switch on the negative side of the battery reduces the potential for sparking, just as connecting the negative battery cables AFTER connecting the positive cables reduces problems with electrical fireworks. However, installing a kill switch on the negative battery circuit leaves the positive side of the electrical system energized.
Machines have caught fire because mice, rats and varmints gnawed through the insulation of energized wires that then shorted-out to the machine’s frame.
Wherever a kill switch is installed, make sure the switch is designed for the maximum amp-load of the starting circuit, because that’s the maximum load the switch will have to carry. Kill switches can be mounted at the battery, hidden somewhere between the battery and starter to prevent theft, or popularly on combines, placed at ground level to eliminate the need to crawl up into the engine compartment to de-energize/re-energize the machine’s electrical system.
