gauge cluster lighting

Its a friends car, the brake light switch went bad while he was at work so he dissconected the positive terminal to prevent the brake lights from killing the battery. when he was leaving work he hoocked the battery back up and then had no dash lights(working prior to battery disconection). he brought the car to me i replaced the brake light switch and the dimmer switch because that is a common prblem in these models thinking it was the issue for the cluster not working. still have no lights to the gauges all check engine and other "indicator" lights work just not the back lighting. Also the positive termenal is loose/wore could this be causing a problem with the lights? runs and drives perfect