1994 Buick Park Avenue 94 park ave starts intermittantly

Electrical problem
1994 Buick Park Avenue V8 Two Wheel Drive 140000 miles

Over a month ago the car began intermittantly not starting. Mechanics changed the starter and when that didn't work, the starter relay. The mechanic said the next step would be going through the wiring harness but I am leery because when I had the same prob with my saturn all of my electrics got screwed up. (As in the horn would go off when you locked the door and lost a bunch of deq sensors) I am wondering if this key relearn thing should be tried first? Is it the same on every year? Is there a way to test it before allowing these people in my wiring harness. Currently the mechanics (they are mobile) have missed our last appointment and are not returning my calls. I don't have money to take it somewhere else and start over. : ( Should mention, all the electronic stuff works when key is turned just nothing from the starter, if I keep trying to start it it generally takes 3 or 4 minutes of constant retrying to start. Other times it starts first try.