Quote Originally Posted by DMCMW Dave View Post
The Lambda relay is marked with an X because in the older all-metal update kits all the relays looked the same, and this one is signficantly electrically different. If you put a common relay in that socket, the freqency valve will not run. If you put the "x" relay in most any of the other common-relay sockets, it will cause most of the grounds to melt in the relay compartment.

Hence the sign DO NOT INTERCHANGE MODULES.
Is there an updated plastic version of the Lambda relay? Or not necessary?