How to Install a Dorman Battery Isolator

dead battery image by Katrina Miller from

A Dorman Battery Isolator is an on/off switch that disconnects the battery from the starter in a vehicle; the alternate name is a battery cut-off switch (although Dorman lists the switch under both names). This isolator can prevent battery drains and also acts as an antitheft device.

It will allow the user to turn a key and disconnect the battery from the starter system, and without the key for the isolator, the battery cannot be reconnected and the car will not run.

Open the bonnet of the car and disconnect the negative cable from the battery by using a wrench to loosen the locknut on the terminal and pulling the cable off.

Decide where the battery cut-off isolator will be placed. Locate the isolator in position that is easy to reach and also allows for the switch to be mounted to the frame of the car.

Mount the isolator switch to the frame of the car using a drill and 2 self tapping metal screws. Drive the screws into the frame of the car through the two brackets on the battery switch. Do not put the plastic key in the switch.

Replace the positive cable of the battery with a longer cable if necessary, to allow the wire to pass from the starter to the switch position and then to the positive post of the battery. Use a wrench to remove the locknuts at both ends of the positive cable, pull the cable out and replace with one of an appropriate length.

Cut the positive battery cable apart so that both ends will reach the terminals on the battery isolator switch. Use the wire cutting part of the electrician's pliers.

Strip a 1/4 inch of insulation of each end of cable by clamping the cable in the appropriate sized wire hole in the electrician's pliers, holding the pliers closed while spinning them around the wire and then pulling the closed pliers off the end of the wire.

Crimp a ring terminal connector onto the end of each cable.

Use a small wrench to remove the locknuts from both terminal posts on the battery isolator switch. Put a wire over each post and lock it in place by tightening the nut back down.

Reconnect the negative battery cable to the battery.

Insert the plastic isolator key into the battery isolator switch and turn it into the "On" position. You can now start the vehicle. Remove the key to disable the starting system.