Fuel and Temp Gauge Question??

Low brake light comes on when your brake pedal goes down to far ( I pushed the switch to make sure it worked) I think I hooked up all the grounds I'll have to double check. Would that cause the two gauges not to work? Also the headlights dim at idle, the wipers and blinkers slow down a lot at idle but as rpm increase they go back to normal. Could this all be tied together?

Thanks
Tom