Take the ECU to your workbench and remove the top and bottom panels from
the case. Take a close look at the board to locate the two areas you need to
be concerned with. This first detail picture shows the header location for
the daughterboard, from the top.
The next picture shows the bottom of the board and the second location,
CJ1 and CJ2. I have seen photos of an ECU with code number other than 62 and
this is in a slightly different location, but it is still CJ1 and CJ2 you
need to locate. The resistor in CJ1 needs to be relocated from CJ1 to CJ2 to
enable the use of an external ROM.
It is interesting that Nissan made allowance for an external ROM in their
original design. It was probably done to allow their engineers to create the
original base map for the ECU. Once the base map was correct, they then
pre-programmed the onboard ROM and the header was then no longer needed in
the final production unit.