electrical prob with wifes 90GT, please help

[Xtreme GT]

When you turn the headlights on,the tach drops to zero,both turn signal indacators come on,temp gauge goes all the way up past 270,fuel gauge shows full. oil pressure gauge is not affected. It is a 90GT stock auto,It was fine then It was parked 3 weeks cause of radiator probs,after I get the radiator in It gives me this problem 3 days later. I've checked the wires under the hood nothing looks shorted or pinched.
Does anyone have any ideas?
Thnks for any help