It's a simple Bosch-style cube relay that can be used as a headlight relay, fuel pump, cooling fan, fog light, or any other device that needs to be turned on/off remotely. The advantage is in using a small-gauge wire from a control switch to operate a heavy-current accessory without running the current a long way to the dash and back.
Most of the relays with a cube housing with 1" dimensions have a 30-amp capacity. There's a 60-amp variety that is a bit larger, about 1 1/2" on each side. The price in the ad above is outrageous- - - -they're on Ebay all the time for about $3.00 each- - - -with connector plugs included.
Jerry
