Emergency brake, battery and fuel light porblem

[wjpfalcons]

I have an HJ60 with a 2H engine obviously 24 v. I replaced the radio (12V) and run it through a 12v power supply hooked up to the 24 v system. Shortly therafter my emergeny light, battery light and fuel light all come on and off periodically. Sometime they stay on for a few seconds and sometime for hours. Truck starts fine and radio/cd work fine. Can't seem to locate the source of the problem.