Can't get rear channel on amp working

[chuey]

I recently got my hands on a JBL GTO 4000 amp and a matching JBL 1000w sub, i have two sets of 6x9's and a set of 5" tweeters also. it's the same amp as pictured but brand
new/never been used. i can get all the speakers, sub included running off the lower "rear" channel but can't get anything running off the upper "front" channel. i've tried just hooking up one set of 6x9's to the rear and just the sub in bridged mode and single channel mode to the front but still nothing. i can run just the sub on its own on the rear and filter it properly but can't get anything out of the front channel in any configuration. is there some way to switch it to three/four channel mode to get power out of the front? am i doing something wrong or is it just that the amp is cabbaged?
thanks in advance!

Click to read more...