Hi JCD:
You lost me here. Is your pump working or not? Are you trying to say that your pump is working when attached to external power supply but does not work when plugged into the car?

By the way Aux pump works only when you have heat function or defrost pressed. It turns off when you are in a cooling mode.

Now assuming that you want to by pass the ACC circuit ( meaning you dont want Aux water pump to use any part of the ACC circuit) yes you can run this pump by itself it needs 12V DC supply- can be obtained from battery directly. This will be te crudest way to do it as the supply is unregulated and will eventually fry your pump. You can put a switch on it as well to turn it odd and on. But if I was you I would see if ACC board can be repaired then do what I did. Put a slow blow inline fuse and thats it.
MVK

__________________
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1985 300D Turbo 179,000miles