question about aftermarket radio - relay
 

I have the Bose system - and an aftermarket Pioneer head unit that I am replacing with a newer unit - upon hooking up the new unit I found this relay - googled it and found this info:

electrical relay 40 AMP - Tyco / replaces Bosch 0 332 209 150

# SPDT
# 40 amp Normally open - 20 amp closed
# 5 terminal - bracket mount
# tyco v23234a1001x036 / 3-1904022-2
# Resistive load normally open: 40 amps @ 200,000 cycles
# ELV compliant
# Also used as a nitrous relay

it is in near the radio, can anyone tell me what this is for? how it should be hooked up? it has five prongs labled, 85,87,a87,86,30

currently the radio turns on but has no sound at all. Speakers worked fine previously.

any help would be appreciated.