Electrical System Cutting Out

[Ragnarok043]

ive recently starting encountering an electrical gremlin and was wondering if anybody else have experienced this before to help diagnose the problem. it happens when i start to decelerate shifting into neutral and step on the brake, the entire electrical system cuts out. first thing i notice is that the radio cuts outs for a brief moment, some times the cluster will loose power as well resetting the clock. other times it would cut in and out rapidly where the tach and speedometer jumps and you can hear relays clicking. at first i thought maybe it was a loose terminal on the battery because it only happens during deceleration but its rock solid and i tested it by jabbing the brake pedal but nothing. plus battery cutting out shouldn't affect power to the cluster with alternator running. i was thinking maybe it could be a bad relay or an electrical short somewhere. BTW i have a KA24DE S13 fastback