Screenwash pump anomoly??

I have noticed something weird on my 1987 730i (m30 engine).

There are two modes on the screenwash steering stalk:

Water wash only. (Pump 1 only).
Screenwash then water wash. (Pump 2 then pump 1).

The water wash function is fine.
The screenwash function seems to feed water only to the jets.

I have unplugged the water wash pump, then pressed the end of the
stalk to invoke the screenwash on its own ... which produced a dribble from
jets (of pure screenwash).
Plugging pump one back in sees the "water" part of the screenwash cycle work
again.

I have swapped the motors over ... same problem.
There seems to be only 6 volts getting to the plug which goes onto
the screenwash pump ... is this correct.
Holding the button in makes the screenwash pump activate its dribble
for 2 seconds, then off for 4 seconds, then on again for 2 seconds.
(Normal?)

Any ideas where to start ... does the screenwash pump have 6 volts sent
to it on purpose??

Maybe its a control module (one of dozens on this car) gone wrong??

B.t.w: The windscreen wipers work when either screenwash mode is used.

--
Regards....
Steve




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