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positive earth question.
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Ray White



Joined: 02 Dec 2014
Posts: 7219
Location: Derby
PostPosted: Sun Dec 07, 2025 7:16 pm    Post subject: positive earth question. Reply with quote
My vacuum pump instructions only refer to a negative earth. As my car is positive earth, should I swap the wires to the pump motor?

Also what about the relay and switch?

I would greatly appreciate some help to avoid making an expensive error.

Please click on link for fitting instructions and diagram. Thank you.

https://www.carbuilder.com/cdn/shop/files/Vacuum_Pump_Instructions.pdf?v=17357643397575415403

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ukdave2002



Joined: 23 Nov 2007
Posts: 4268
Location: South Cheshire
PostPosted: Sun Dec 07, 2025 9:07 pm    Post subject: Reply with quote
All you need to do is reverse the pump connections, so the red pump wire goes to 5 and the black to 2. Everything thing else stays the same, unless the relay has a diode built in, in which case swap 1 & 2 (relay coil ) around.
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Ray White



Joined: 02 Dec 2014
Posts: 7219
Location: Derby
PostPosted: Sun Dec 07, 2025 10:48 pm    Post subject: Reply with quote
ukdave2002 wrote:
All you need to do is reverse the pump connections, so the red pump wire goes to 5 and the black to 2. Everything thing else stays the same, unless the relay has a diode built in, in which case swap 1 & 2 (relay coil ) around.


Thanks Dave. That has really helped me. I don't see a diode symbol on the relay so I presume it is not there.
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