Does anyone know if dealerships will allow you or work with you on making payments on extensive mechanic work? ie: possible new transmission, and wiring problems.
Usually not. I worked for Goodyear for almost 5 years and we never let the vehicle go without having the full amount paid. Some places offer credit cards or they have local banks set up to approve high interest loans. Unless you know the owner of the shop really well you'll have to pay before picking your vehicle up.
Some transmission shops have access to their own credit card, much like GoodYear, where you apply and depending on your credit they accept you and you make the payments.