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MG MGA - Convert Positive Earth Fuel Pump to Negative Earth

One for D.W. DuBois, I suspect. I need a Neg earth fuel pump, but there is a massive 12 week delivery time with most sellers out of stock. I have a spare, unused, SU Positive Earth fuel pump; can i convert something inside so it can be used Negative Earth?

regards
Colin
Colin Manley

If it has points and a diode, reverse the diode
es1

Colin - Send me a picture of the top of the pump with the end cover removed and I can tell you exactly what to do. Send to SUfuelpumps@donobi.net Cheers - Dave
DW DuBois

Colin, Have you tried the MGOC spares dept, Telephone order Lines: +44 (0) 1954 230928 & 231318
I bought a new neg earth pump from them 2 weeks ago and they were the best price. You don't have to be a member.
Paul
p anderton

As i recall, this positive earth pump is a 'pointless' type.

Dave,
Photo attached. Is it as simple as swapping round the Red & Black wires?

regards
Colin

Colin Manley

"Is it as simple as swapping round the Red & Black wires?"

Yes, but you may have a hard time with the lead length. You can purchase a dual polarity arc suppressor from Burlen Fuel Systems to replace the existing diode - P/N CZX 1004 the price is 4.33.

"As i recall, this positive earth pump is a 'pointless' type."

The only polarity sensitive pumps today are the all electronic versions. All of the dual polarity, points style pumps use the above quoted arc suppressor. Cheers - Dave
DW DuBois

Colin - I bought a negative earth fuel pump last week from MGOC - ordered Tuesday and delivered the next day. (Part No. AZX1331). Price was 114.05
I suggest getting the packing rubber as well (AAA260). There are no fibre washers included - mine leaked when I connected the unions, so I put on a couple of washers to cure it.

D J Hill

Dave, If i read your full words correctly, as i (i think) have an electronic pump it is polarity sensitive. Hence i need to modify it. It has Red tape around it, indicating Positive Earth.

Do i also need to swap the small wires that appear to come out of the innards of the pump to the terminals of the Red & Black wires or just the diode wires? I only ask as the Red & Black wire length of the diode looks like it will transpose OK.

regards
Colin
Colin Manley

Colin - I may have misled you. The picture you posted is of a points style pump with a diode/resistor assembly for arc suppression that is wired for positive ground. If you can switch the leads of the diode/resistor assembly around, the pump becomes negative ground. If you get the varistor that I gave you the P/N for and install it, you pump becomes dual polarity - in other words, it will work for both negative or positive ground.

"Do i also need to swap the small wires that appear to come out of the innards of the pump to the terminals of the Red & Black wires or just the diode wires?"

You just need to swap the red and black wires from the diode/resistor assembly. The other wires go to the coil, which doesn't care which way it is wired. Cheers - Dave
DW DuBois

Dave,
Thank you. Wires swapped and pump whirring away (no fuel yet) on test.

The lead length was OK.

regards
Colin

Colin Manley

This thread was discussed between 25/06/2015 and 26/06/2015

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