An isolator is used to combine two batteries when an alternator is charging ( engine running) and isolate them when not charging ( engine off) so you can still start your vehicle. Connect the two small studs one to ground the other to an ignition on source from fuse box , the order on the large/ small studs does not matter 2 copper points, housing, galvanized steel housing / flat mounting bracket. Voltage: 24V Colour: silver Material: metal Size: 85.3 x 67.4mm Package Contents: 1 x relay Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.