2000 vnl 770 bunk speakers not working

Some head units need to be programmed for 2 or 4 speakers, did you have this option?

 

A majority of the early VNL770's had an amplifier that powered the rear subwoofer and rear speakers.

The amplifier is located in the left upper cubby storage hole on the passenger side above the door window.

 

I had the same issue 2010 VNL730. This info. I'm giving you is from Volvo themselves. Most Volvo's come with the 4 bunk speakers installed with the factory lume plugged into the speakers. The problem is that lume might only be 2' long or it might go all the way to the radio ready to plug in. So I asked the guy why the hell would Volvo put $400 worth of speakers in a truck and not hook them to a radio. He said "EXACTLY" Anyways if you don't have the amplifier on the top right storage area then you will have to do what I did. Take it to a good stereo shop (not a Volvo dealer) and have them install an amp and run the wires the rest of the way from the bunk to the radio. While my truck was there I also had them put an alarm on the truck with a pager so if anything happens to it and I'm not there it will alert me. Also if you have the work station some Volvo's come with a 5th speaker. A sub-woofer located inside where the hvac system is.