after-run coolant pump question

[Jouko Haapanen]

I am about to be reunited with my UrQ after a 10 month separation, as
I go back to Finland for my holidays.  The after-run coolant pump is
not operating, but I just received word that the pump does respond to
12 volts as it should.

The current flow diagram (No.39 for model year 1988, parts 1-4, engine
code MB) indicates a thermoswitch F98 and a switch unit (relay) for
coolant pump J155 and coolant pump V51 as the parts for this system.
Not having the car real close to me it is a bit difficult to diagnose,
but is the relay a possible culprit?  I can't tell you if the injector
cooling fan works, as I removed that some time ago.  It appears that
the relay unit (J155) is located on the additional relay carrier under
the instrument panel in location 5 (middle row, fifth from left).  Do
these have any history of failing?  I would think that the
thermoswitch is less likely to fail.  Or not?  The factory workshop
manual GB 000.5147.00.20 from 10.87 outlines the diagnostics on page
19-17.  The diagnosis is carried out with the VAG1527 diode check
light tool.

There are two different relays specified by ETKA for this location as
"relay, for relief relay x contact, relay location 5" part numbers 191
937 503 (12V40A) as well as 357 906 381 B (12V70A).  Which one is the
right one?

The patient is a 1988 MB engined UrQ.

Any ideas?

Jouko Haapanen