It does sound like it's time for a new timing chain. Here's a pic of where the stock oil sender goes, and you should look for a purple wire in your harness to connect to it. Just find the purple wire under your dash, hook it up to your new gauge and you should be good to go.
'77 CJ-5 Renegade 304 / T-150, Dana 20, 30/20 axles, Aussie Locker in the Dana 30, American Racing 15x10 Outlaw II's, 33" Dynapro M/T's" ,Optima Battery, TeamRushed + Summit Racing CDI ignition, FlowKooler water pump, Edelbrock Performer Intake Manifold, Holley 4160 390cfm, Herculiner, Silver Ceramic Coated Hedman Hedders, Flowmaster 40's.
Warn PowerPlant HD 12K Winch, Dirtworx front and rear bumpers.