IBM RT User's Setup Manual page 279

5-6 Options Installation
If you need to reset the switches, use an opened paper clip or a
ball-point pen to do so. Set the switches as shown in the following
drawing:
Warning: Do not install this adapter in slot 8 in IBM 6150 or
in slot 5 in IBM 6151.
This adapter can be installed in adapter slot 2, 4, 5, or
Installing:
7 in the IBM 6150 and in adapter slot 2, 3, or 4 in the IBM 6151.
See the system unit diagram to locate the adapter slots.