This is probably going to be obvious to everyone else, but for the last 3 years of owning my 1994 D1 I've complained to myself that the radio volume didn't get loud enough to hear over highway road noise.

I had been suspecting an aging amplifier but the other day realized that the volume controls + / - on the instrument surround operate independently of the pioneer head unit volume ****...!

Once I used the instrument surround button to increase the volume it was super loud and easily heard over road noise. This was confusing to me since I thought the parallel controls operated the way modern steering wheel volume does (i.e. both the **** on the unit and steering buttons change volume over the entire range). However it seems on the D1 the Pioneer unit **** just modulates volume from 0 to whatever the instrument surround button is set to.

Anyway...one less thing to replace!