It may be because MRC and Tsunami's don't handle light control the same way.Could you post a schematic of the wiring?
It seems that the LED board may be the cause...are all the lights fully independent from eachother?I've had a weird problem when I replaced a Paragon 2 decoder with a Tsunami...P2 powered the ditch lights differently.
I have replaced the OEM MRC decoder with a Tsunami TSU 1000 Heavy Steam decoder in an Athearn Genesis FEF #838 I purchased new in about 2008.
I tried using the OEM PCBs in the loco but they just seemed to cause problems - so I have removed both of them but left the small PCB that is used to mount the SMT LEDs for the headlamp and Mars light.
The loco seems to run fine and respond to my NCE Power Pro system generally, but I have been unable to complete the set up for the lights because the main headlamp, the Mars light and the reversing lamp are constantly on, the lights do not go out when the dynamo is cycled off and the Function 5 (which I have used for the Mars light) does not turn that light off but does turn all the sound off (as does the Function 8 button).
I have tried addressing these issues with Decoder Pro 3 and the program track settings for the NCE Power Pro - but neither method corrected these problems.
I would be grateful for any suggestions on how I might fix up these issues.
Many thanks for you interest in my post.
Regards,