Headunit voltage drop, need help!!!

[thaster 10+ year member]

i am trying to install my pioneer premier m680p headunit into my g20 and the headunit won't turn on. I used a DMM and found out that the wire harness read 12 volts but when i connect headunit power wire to the harness, it now reads 5 volts. I then try to connect the harness power wire to the acc wire and it read 9 volts. Anybody know what the problem is?

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[thaster 10+ year member]

anyone?

 

[thaster 10+ year member]

help please