check engine light and loss of brake pedal

Two different Safaris that I have had were of the same vintage as yours. Your comment about working on the batteries really rings a bell. Safari was real good at connecting both positive and negative smaller gage wiring to terminals on the batteries (both house and chassis). When changing batteries or cleaning terminals or doing other chores where wires were disconnected it was real easy to lose a wire or two over behind the battery drawer. It is really important to mark these wires when you take them off as to terminal type, Plus or ground. If you don't you will need to wring them out before reconnecting so you don't get them in the wrong place. As far as the brake problem is concerned I think that is a separate issue.