Fuel Gauge

[Donald Carmichael]

My 1964 Roadster was converted to negative earth many years ago. I have just recently replaced the fuel tank with the original type and correct sender unit. This sender would be for a positive earth system so my fuel gauge now reads full when empty and empty when full. I have tried reversing the wiring but no difference. When previously fitted with the later type tank and gauge all worked as it should, but the later type sender does not fit this tank. Any suggestions for a quick fix?
Donald Carmichael.

[Peter Cresswell]

Hi Donald,
It is obviously a polarity problem, but I'm not sure it has a quick fix. I say this as I drove Gerry Browns FIA car a couple of years back and his gauge read backwards. I his case he had simple painted new marking onto the glass, so if Gerry couldn't make it work properly then I would doubt the is a quick fix. Remarking is ok on a competition car, but not what you want on a road car!

[Donald Carmichael]

Thanks Peter, I've put red and green stickers on the glass to remind me but only a temporary solution. Going to see an auto electrician tomorrow. If he has a solution I will let you know.
Donald.

[Peter Cresswell]

Hi Donald,
This might offer some clues, and (between the 'stars') is from the Minispares site for converting a Mini from dynamo which is positive earth to alternator which is negative earth. So a similar conversion to that done to your MGB, and this information might help you or your Auto Electrician.
******************************************
CHANGING FROM DYNAMO TO ALTERNATOR
Keith Calver

30/07/2005 14:26:00
Completing this change successfully, easily and neatly is pretty straightforward on a Mini. The alternator contains the regulator and cut out functions within it’s casing, so makes the regulator box used with a dynamo redundant.

Part No Applications: GEU205, GEU205MS, GEU207, GXE2297
However, it is useful to retain the box itself and it’s connectors. It acts as a terminal box to make the installation neat, avoiding the messy and awkward soldering/taping together bunches of wires. It also maintains a period look, plus makes reversal easy should this be needed in the future.

Disconnect the battery and remove the black regulator box from the car - taking care to make a note of or label each wire removed with it’s original terminal connection. Fit the alternator using the necessary rear support bracket (part no. 12G1053) as the alternator is shorter than the dynamo. The relevant belt (GCB10825) is also needed. The alternator has a smaller diameter pulley to drive it at a higher speed than a dynamo, giving better output and therefore battery charging at lower engine speeds.

Take the regulator box cover off and dismantle it. Remove all of the coils, contacts and connections to the blade terminals on the bottom of the unit, but retain the blade terminals. Double check that all connections to the terminals are removed, then using some heavy cable - 2.5mm or larger - solder links between terminals A, A1, and D, connecting all three together. Now solder a link between terminal F and E. Replace the box in the car and re-connect all the wires to their relevant terminals except the ignition warning light wire (brown/yellow) which must now be connected to terminal E. Connect the ex-dynamo wires to the alternator - large connector to the large terminal (output connection) and the small one to the small terminal next to it (sensing terminal).

If the car being converted was already negative earth, re-connect the battery and away you go! If the car was positive earth, you will need to reverse the connections to the battery and swap the connections on the ignition coil.

If there is a radio or cassette player fitted, check to see if these can be re-connected as negative earth. If not, then unfortunately they will need replacing. Everything else should work as normal.
***************************************
I did convert my Mk1 Mini Cooper from dynamo to alternator, but I didn't keep the regulator box as a junction box, but I rewired the alternator completely to the fuse box. All I did then was swap the battery leads over so negative went to earth (the cars body). I didn't have any problems with the gauges, which all continued to read normally. However it was a 1967 car which didn't have a voltage stabiliser, which the earlier cars had and also the MGB up to 1967 when they went from dynamo to alternator so this something to consider as well.
However I think favourite must be to do with the earlier tank sender unit you now have having fitted the earlier tank. Maybe your car acquired the later tank when it was converted to alternator and negative earth simply because they couldn't make the gauge read correctly without doing this.

[Donald Carmichael]

Thanks to all posters. I think I have found the problem with my fuel gauge. For a short while after changing from Jaeger to Smiths instruments the Jaeger tank sender was incompatible with the new fuel gauge and a new sender was introduced to fit the early type tank. Shortly after this the later type tank was introduced with a different fitting for the sender. I had the later tank but replaced it with the early type and fitted a Jaeger sender, hence incompatible with my Smiths gauge.
Does anyone know where I can get an early type sender compatible with Smiths gauges? Both MGB Hive and Moss are out of stock.
Donald

[Peter Cresswell]

Hi Donald, I take it you need sender unit part no. BHA4471E. It is listed here:

http://www.mgpartsuk.co.uk/store/index. ... 30_306_247
and you can contact them either via their website or

Midland Sports & Classics Ltd
Unit 19 Wilden Industrial Estate
Wilden Lane
Stourport on Severn
Worcestershire
DY13 9JY
01299 829000
email sales@msc.parts

Although Brown and Gammons are a bit ambiguous about this part no. on their website, they are probably worth a call on 01462 490049 and ask to speak to Malcolm Gammons.

[Donald Carmichael]

Thanks Peter. mgpartsuk are out of stock but I found one at jagparts, Abingdon. It comes in at £180. I thing I'll change the tank!

[Adrian Oliver]

Donald, I'm intrigued.

How did you swop fuel tanks when the early strap on and later bolt on types are totally different?

[Donald Carmichael]

Hi Adrian, the original brackets securing the straps were cut off to accommodate the new tank. I replaced these then fitted the original type of tank using new straps.
Donald.

[Adrian Oliver]

Moss have them in stock for £34.

http://www.moss-europe.co.uk/sender-uni ... a4292.html

As for any other problems with the negative earth conversion, why not revert to positive earth?

It keeps it original and you can buy a positive earth alternator that looks like a dynamo now too.