I am a Master Technician of 12yrs for a high end line (dealership). I do not know anything about running a business. An acquantence of mine opened a specialty shop a year ago and has asked me to join in. He has offered a high flat rate and a percentage of total sales. His diagnostic abilities are not the best and I would be diagnosing and instructing most of the time. Due to the lack of finding excell help he is down to himself and swamped with work. My ? is what to ask for?? A salary, a percentage of the store, a parnership, total anual sales, overhead, etc..? What info should I abtain ahead of time so I dont get screwd???

I would try to come in at least being a partial owner. You may want to talk with him about buying in to become a 50% partner. It would be in your best interest and help him get out of his bind.

Consult a LAWYER! prior to entering into a partnership.
There is a lot that can go right, but a lot more could go wrong.

Agreed. You will need a lawyer. You need someone to go over all of his books (financials) and give you advice, etc.