Oldsmobile/Buick Repair: Buick will not start., buick v6, coloumn

Question
Have a 97 buick V6, that will not start every time. took it to repair and said it was the battery terminals.  He cleaned them. Ran good for a while.  Started to not start again unless we banged on the dash or wiggled the steering wheel. Called same repairman and he said pour h2o and baking soda.  Started up okey.  Why is it that if we bang the dash, or what ever, she will go. When it starts it will for the entire time with out cutting itself off.  I can not tell if bad gnd or bad hot wire.  Computer?  My repairman put it on a diagnostic machine when he fixed it 1st time

Answer
hi jim .well what you didn,t say is when it don,t start do you mean it won,t crank.or cranks ok but will not start.since your mech was able to clean cable ends and start it i would have to assume it don,t crank.if this is the prob and you get it to start by tapping on the dash or especially turning the steering wheel that you have a prob right near the steering coloumn.and the only thing there is mounted to the top of coloumn is a switch.this is called a ignition switch not a lock and key but a electric switch.there is a flat bulk of wires that plugs into this switch.MAKE SURE THE PLUG IS CONNECTED AND SNAPPED.if it is you will need to replace this switch they vary from 20.00 to 50.00 in price.if you are going to replace this yourself.there is a rod that goes in the back of this switch be sure it goes in the right spot.your lock and key moves this switch and cranks the car.now this all is only because you said you can tap the dash and move wheel and start it.good luck jim.  billymac