Volvo: 1992 240 rhythmic power loss, fuel pump relay, rhythmic power

Question
My '92 240 will operate perfectly, then all of the dash lights will start blinking once per second, the engine will lose power at the same interval.  Sometimes it will stall, sometimes within a few minutes, it will correct itself and everything will be ok.  Sometimes you hear relays clicking behind the radio.  I have opened the car before and heard a clicking sound inside the radio.  I finally disconnected the radion, but still have the problem.

Answer
Sven,
When this happens is there power loss to the coil? Do you loss power to the fuel system? Is the charging system in good working order? Have you checked all the possible wire conncetions for corrosion and tightness? Could it be that the charging system fails and there is not enough power to the pumps and coil? Does the ignition electrical switch feel loose and at time when you move it cause some power loss to accessories? Is the wire harness under the hood all frayed, by the rear of the engine? Are you loosing fuel pressure when this happens? Are the fuses heating up in the box causing poor connection? Battery ground cable along with the positive all have good contact, both ends?
Check for fault codes maybe you have an MAF or Flywheel pick up going bad. Is the fuel pump relay newer? How about the radio suppression relay for the injectors?