ATTENTION: All Postings that advertise items for sale will be deleted from the Discussion Forum. You may post sale items for free in the Classifieds section. Sign up now.
The reverse relay on your 4106 may not be your problem. Doublecheck:
They are just like a starter solenoid, and kind of difficult to troubleshoot. Mine gave me trouble so I got a new one, and it did exactly the same thing as the old one.
With the bus running, have someone push the button and pull it into second gear while you check voltage at the solenoid terminal to mounting bolt (ground). If it drops to 11 V or less, you may have dirty contacts or bad control relay. This was my issue, and a cheap fix for the ferrari of busses.