For an L400 I wouldn't bother with a turbo timer.
L300 with the smaller 2.5TD, yes but the L400 with the 4M40 2.8, nein !
After hooking up an egt/oil/water temp analogue gauges and watching the temps between a hot shutoff and a hot shutoff w/1min timer, the temps are so minimal it's not worth it.
Just adds more complexity to your electrical starting system.
Given the choice these are my recommendations to keep the engine running cool in priority
EGT/Boost gauges - monitoring
2.5" exhaust - more hot exhaust flow
If you want a turbo timer regardless, I would go with a proven one. Greddy universal. It's what you see on lots of JDM's.
Mitsu Eclipse will be the right harness.
http://www.alamomotorsports.com/greddy/grtimer.htm