Hi pressure line return and 3rd line on W108 steering box - can it be blocked off?

Shaun - I can confirm the three connections on the W108 power steering box:

1. High pressure inlet (from pump): the upper-rear banjo fitting, 16mm fitting
2. Low pressure return (to reservoir): the lower-rear banjo fitting, 14mm fitting
3. Third line (the one with the red question mark arrow): this is the kickdown signal line - sends a pressure pulse to the 722 transmission valve body to trigger kickdown under heavy throttle.. NOT a hydraulic feed - just signal pressure.

Since you've gone non-stock running gear (the LS swap from the PO), the kickdown signal line is no longer connected to anything useful. Yes, you can block it off. Use an M10x1.0 plug with copper crush washer at the steering box port. $6 at any bolt shop. no leaks, no functional loss..

For anyone reading with a stock W108 4-speed auto: do NOT block this line. Kickdown will not work and the trans will hold gears too high. It's only acceptable to block it if the original 722 auto has been removed.