Well you had me scratching my head with this one, what on earth is an "arb". At first I thought maybe the C on your keyboard was sticking and you meant "carb". However you refer to an AMC20 which is an axle so you are referring to a ARB air locker?
There is an o ring seal in the housing that you will want to replace as a matter of course and of course the nylon air line and fittings up to your compressor. The relay and solenoids and wiring kit should be good to go and the locker itself is pretty reliable.
BagusJeep lives in Bali.
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1947 Willys CJ2A/3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE