280c Battery Light Stays on when Key removed
I am new to forum, and in process of purchasing a 1975 280C with approx 80k miles in overall great condition. Problem is the owner was trying to charge battery for a test drive and connected the battery charger to the wrong terminals (replacement NEG cable was red).. We were able to jump start the car and drive it a short distance. When car is off and key is removed the BATTERY indicator stays on, and goes out when you drive. I know its not charging the battery because I can only go a short distance before car dies and needs to be jumped again. We tried a couple of new batteries and same thing happens. Before I spend the $$ for the car, would like some advice of things to check first. I did drive the car before this happened over the summer and she is really smooth. Any leads would be appreciated.