1991 240 radio cuts out

[vcowens]

hello everyone. I have a working amplifier located behind the console. I plugged it into the radio however it only plays amplified if i jiggle the radio harness. Does this sound like a grounding issue or a radio issue? should the amplifier be grounded? Also the radio is no longer attached to the mounting bracket on the firewall. Does it need to be in order to provide grounding? I haven't been able to find a schematic. Thanks