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Main Section => Welcome to our virtual Pub Meeting ... => Topic started by: 109 fever on March 22, 2021, 09:59:39 PM

Title: the old fuel gauge conundrum
Post by: 109 fever on March 22, 2021, 09:59:39 PM

I bought a new old stock + ground sender unit for the '66 109 SW.  turns out the original one was frozen for lack of use by the prior owner. Freed it up and now working.
  I just picked up a '62 109 2 door and the sender is no good. 
1.  can I use the + ground sender on the -ground truck, and if so, 2.  will it read backwards or upside down?

Thanks for any comments.

Title: Re: the old fuel gauge conundrum
Post by: Dormy on March 22, 2021, 11:08:25 PM

The answer is in the instruments. Both a 62 and a 66 should have been + ground originally unless part of some specially requested order (my L/R is Aug 66 and had + ground).

As long as they are matched together the instruments and senders don't care if the vehicle is + or - ground, they will continue to work correctly and don't need any swapping at the time a vehicle is converted: -

1. If you have an arrow type needle in the gauge then the vehicle should have a "+" ground sender unit.

2. If you have a straight needle in the gauge then vehicle should have the later "-" ground unit and a voltage stabiliser.

The problem you might have is whether a PO has swapped things around. The later "-" sender unit has significantly different resistance as well as working the opposite way to the earlier unit, so isn't compatible with the earlier gauge.

Best check which instruments you have so you can establish whether you need an early or late sender.

HTH
Dormy

Title: Re: the old fuel gauge conundrum
Post by: 109 fever on March 23, 2021, 01:17:26 AM

thanks Dormy.  I did not consider that the '62 109 had been converted from +ground to -ground (it has a new wiring harness).  Both '62 and '66  have the pointer gauges.  I wonder if my NOS sender unit will even fit in the petrol tank under the front seat.  The '66 has the saddle tank in the rear.  I have not seen the '62 yet.  Is the tank a different configuration?

Title: Re: the old fuel gauge conundrum
Post by: Wittsend on March 23, 2021, 01:37:04 AM

The tank senders are not polarity conscious. The senders are the same for the LWB & SWB tanks. It's just that the SWB tanks/senders are easier to access.

You need to match the right sender to the correct gauge.

(http://www.series2club.co.uk/gallery/technical/images/fuel_gauge_and_sender-early.jpg)

(http://www.series2club.co.uk/gallery/technical/images/Fuel_gauge_ and_sender-late.jpg)



 :RHD

Title: Re: the old fuel gauge conundrum
Post by: 109 fever on March 24, 2021, 02:09:21 AM

Thank you.  If the sender units are not polarity sensitive, then I am ok.  The arrow head gauge with the sender unit you show are what I have in my '66 109.  The '62 109 two door hasn't arrived as yet.  But I know it has the arrow head indicators and my NOS sender should go right in.  Push comes to shove, I have a NOS arrow head gauge.  (they came hermetically sealed originally)

Title: Re: the old fuel gauge conundrum
Post by: Wittsend on March 24, 2021, 11:30:41 AM

To get the best "connection" you should have a dedicated earthing wire from a tank sender fixing screw to the chassis nearby. You can't rely on the tank fixing bolts to provide a good earth.


 :bright-idea