battery repl. Now, dash lts go dim when I turn on head lts. No engine light

Just because you got a new battery doesn't mean you have the right battery or a good battery. If you buy your battery from a reputable place i.e. Sears, napa etc. They will put the acid / waterin infront of you. Unless you are getting a sealed cell no service battery make them do it otherwise you could be buying a battery that has been on the shelf corroding inside for years. Also check first all your wires are not swollen or overly corroded. Sounds like you got too small (not enough amperage output) of battery. Cheap and fits doesn't always cut it with batteries.

IF I'm understanding you correctly , your problem now is not with a dead battery or weak alternator , your problem is that the dimmer setting for the gauge cluster defaulted to the lowest setting when the battery was disconnected. is that something you've checked?