Howdy,
The 5G8 identifies it as a xj750RJ.
The first three # identifies model and year of manufacture.
The last info I have is 5G2 which is 1982.
Luck to you.
armydog1
Hey partner, sounds like a starter relay, or CDI ignition igniter. The starter relay can be checked with a jumper wire between terminal studs located on either side of relay. Good luck.