Can you help me fix the wiring in my car radio?

There is is problem with the wiring in my car. I cannot listen to the radio at the same time that the headlights are on. This started occurring after my older brother and a friend installed a new radio. As far as I know there must be a mistake in the wiring but I cannot understand what could be causing it. If the radio is on and then the lights are turned on then the radio goes out, and when the lights are turned off the radio comes back on. If the lights are on and you try to turn on the radio then the radio is unresponsive. Please help me. Is it just a faulty wiring job of is the problem more serious?