i had a similar problem as you with my speedo cluster. all of my lights were burnt out so that was the first problem and then i have to play with turning the light switch left and right to get the speedo lights to work. once i find a good spot they stay on fine, but it had me a little perplexed at first.
congrats on gettin a jeep and a 79 at that!
'10 Wrangler Sport, soft top, hard doors, 23S package, Teraflex 2.5" spring lift, Spidertrax 1.5" wheel spacers
'79 CJ-7 Renegade, 258 I6, T150, D20, D30/AMC20, 2.5in Rancho lift, 31x10.5 AT's, TeamRush upgrade, flush tail lights - Sold :'(