Fuel and Temp Gauge Question??

Well it isn't the brake lamp, it's all the lights are dim, wipers are very slow, blinkers are slow ect. until I rev the motor a little then they all brighten and speed up. I did install the noise suppressor right where it came from. I'm leaning towards a bad chassis ground. Can anyone tell me where I can locate them? I checked the one from the neg. terminal to the block are there any others?
Thanks
Tom