Help...wtf?? Power Issues??

Everything has worked well in my cab up until recently. Now, when my digital HID light comes on the fan speeds slow down (permantly) an the room lights dim (only for a brief second). The slower fan speeds (inlet and outlet) have affected my temps by about 5 degrees. Has this happen to anyone before? If it was always like this I would understand...but these things have been running for months and all of a sudden this has happened.

Try connecting everything, except the light, to a different circuit. See if it still happens. One thing that could cause something like this over time would be if the wiring you have is 14 wire instead of 12 wire or if its aluminum wire instead of copper. To start with it will run ok but the wires will weaken over time. Another thing is using a 15 amp breaker instead of a 20 amp breaker. Works fine for a while but gradually weaken the breaker.
You need to investigate this problem thoroughly. VV