If you have a long head Mark IV B the rocker switch for the eq is on the front. It is positioned between the Output Level control and the eq sliders. There are two black rocker switches. The one you are looking for is the top switch. It has three positions. All the way up is the R2 auto select (the position you are looking for), middle is off and down is on. Hope this helps.
The amplifier for a long/med head and a wide body combo are the same. The only difference is the enclosure. Sorry for the confusion. Check for the rocker switches as I first pointed out. You should find it there. As Shep suggested pictures of the front and back would help if you are still having problems.
Sorry guys, I didn't happen to see the rocker mounted on the front... to the right of the GEQ. The top portion of the switch that says R2 Auto was hidden from my perspective... **** pilot controls :twisted:
