Need help: One Fuel Guage wiring

[Brett James-McCall]

So I need some help from all you experts

I am going to run only one fuel gauge in my car and would like it to show the active tank/pump. How can I get this to work?

I'll be using a Lucas On-On switch to change tanks using a SouthernGT loom

Here's the connections for the On-On switch

 

[Glenn M]

Hi Brett

Assuming normal Smiths type gauge;

regulated +ve to gauge as normal, then other side of gauge (normally to sender unit) to switch number 1 or 7,

2.....to one sender unit

4......to other sender unit

hope that's clear, I haven't got a clue how to post drawings which would be clearer and save all this typing!

Good luck, Glenn

 

[Seymour Snerd]

Glenn --

Just to clarify: are you suggesting that Brett add another34889 switch to select senders? Or are you suggesting he do that wiring to the existing switch that is currently selecting tanks?

 

[Jon Briggs]

I always thought you would need two switches, or at least some sort of relay set up.

Would be very happy to be wrong though. I wanted to do this with mine, if I ever get to this stage!

 

[Brett James-McCall]

Re: Need help: One Fuel Gauge wiring

Yes, I would like to run only one switch, so that it swithes the tank and then at the same time switches toshow the level in the active tank.

I've done this so I can have a different dial in the dash rather than two fuel gauges (Fuel, Volts, Oil Pressure, Oil Temp, Water Temp)

Here are the relevant connections I can see on the wiring sheet for the fuel pumps and gauges. (I have Jaguar solenoids that I will be wiring in parrellel for each tank to stop cross flow)

Any further help and advice would be great on this.

<TABLE style="WIDTH: 287pt; BORDER-COLLAPSE: collapse" border=0 cellSpacing=0 cellPadding=0 width=382><COLGROUP><COL style="WIDTH: 97pt; mso-width-source: userset; mso-width-alt: 4717" width=129><COL style="WIDTH: 81pt; mso-width-source: userset; mso-width-alt: 3949" width=108><COL style="WIDTH: 109pt; mso-width-source: userset; mso-width-alt: 5302" width=145><TBODY><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: windowtext 1pt solid; BACKGROUND-COLOR: transparent; WIDTH: 97pt; HEIGHT: 60.75pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 0.5pt solid" class=xl64 height=81 rowSpan=4 width=129>L/H FUEL GAUGE</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; WIDTH: 81pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 0.5pt solid" class=xl65 width=108>GREEN/BLACK</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; WIDTH: 109pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid" class=xl66 width=145>FUEL SENDER</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl63 height=20>GREEN</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl68>SWITCHED POWER</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl63 height=20>RED/WHITE</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl68>FUSE ILLUMINATION</TD></TR><TR style="HEIGHT: 15.75pt" height=21><TD style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15.75pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl70 height=21>BLACK</TD><TD style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl71>EARTH</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: windowtext 1pt solid; BACKGROUND-COLOR: transparent; HEIGHT: 60.75pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl64 height=81 rowSpan=4>R/H FUEL GAUGE</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl65>GREEN/YELLOW</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl66>LOOP L/H FUEL GAUGE</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl63 height=20>RED/WHITE</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl68>SWITCHED POWER</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl63 height=20>GREEN</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl68>FUSE ILLUMINATION</TD></TR><TR style="HEIGHT: 15.75pt" height=21><TD style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15.75pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl70 height=21>BLACK</TD><TD style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl71>EARTH</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: windowtext 1pt solid; BACKGROUND-COLOR: transparent; HEIGHT: 45.75pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl64 height=61 rowSpan=3>FUEL PUMP SWITCH</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl65>ORANGE/GREEN</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl66>RELAY 87</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl63 height=20>ORANGE/BLUE</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl68>RELAY 87</TD></TR><TR style="HEIGHT: 15.75pt" height=21><TD style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15.75pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl70 height=21>GREEN</TD><TD style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl71>SWITCHED POWER</TD></TR></TBODY></TABLE>

 

[Paul]

Put in a 3 position switch like a headlight switch - off, tank one, tank 2.

 

[Seymour Snerd]

Re: Need help: One Fuel Gauge wiring

Yes, I would like to run only one switch
<TABLE style="WIDTH: 287pt; BORDER-COLLAPSE: collapse" border=0 cellSpacing=0 cellPadding=0 width=382><COLGROUP><COL style="WIDTH: 97pt; mso-width-source: userset; mso-width-alt: 4717" width=129><COL style="WIDTH: 81pt; mso-width-source: userset; mso-width-alt: 3949" width=108><COL style="WIDTH: 109pt; mso-width-source: userset; mso-width-alt: 5302" width=145><TBODY><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: windowtext 1pt solid; BACKGROUND-COLOR: transparent; WIDTH: 97pt; HEIGHT: 60.75pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 0.5pt solid" class=xl64 height=81 rowSpan=4 width=129>L/H FUEL GAUGE</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; WIDTH: 81pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 0.5pt solid" class=xl65 width=108>GREEN/BLACK</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; WIDTH: 109pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid" class=xl66 width=145>FUEL SENDER</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl63 height=20>GREEN</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl68>SWITCHED POWER</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl63 height=20>RED/WHITE</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl68>FUSE ILLUMINATION</TD></TR><TR style="HEIGHT: 15.75pt" height=21><TD style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15.75pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl70 height=21>BLACK</TD><TD style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl71>EARTH</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: windowtext 1pt solid; BACKGROUND-COLOR: transparent; HEIGHT: 60.75pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl64 height=81 rowSpan=4>R/H FUEL GAUGE</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl65>GREEN/YELLOW</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl66>LOOP L/H FUEL GAUGE</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl63 height=20>RED/WHITE</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl68>SWITCHED POWER</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl63 height=20>GREEN</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl68>FUSE ILLUMINATION</TD></TR><TR style="HEIGHT: 15.75pt" height=21><TD style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15.75pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl70 height=21>BLACK</TD><TD style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl71>EARTH</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: windowtext 1pt solid; BACKGROUND-COLOR: transparent; HEIGHT: 45.75pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl64 height=61 rowSpan=3>FUEL PUMP SWITCH</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl65>ORANGE/GREEN</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl66>RELAY 87</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl63 height=20>ORANGE/BLUE</TD><TD style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl68>RELAY 87</TD></TR><TR style="HEIGHT: 15.75pt" height=21><TD style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; HEIGHT: 15.75pt; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 0.5pt solid" class=xl70 height=21>GREEN</TD><TD style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext; BACKGROUND-COLOR: transparent; BORDER-TOP: windowtext; BORDER-RIGHT: windowtext 1pt solid" class=xl71>SWITCHED POWER</TD></TR></TBODY></TABLE>

OK that's what I figured. I'm assuming that the fuel gauges pass switched power to the sender through a resistance in the gauge, and that the senders are just a variable resistor with the other side earthed. Thus when the sender resistance changes, the sender voltage changes and the gauges positions accordingly.

If that's true I can think of two was to do it:

1: a garden variety relay like this:


You would connect it up as follows:

86 earth
87 fuel pump siwtch orange/green
30 gauge fuel sender terminal
87 fuel sender for same tank as "organge green"
87a fuel sender for other tank.

Thus, when you turn on the "orange/green" pump, the relay is energised which connects the gauge's fuel sender terminal to the fuel sender for that same tank. When you turn on the other pump, the relay de-energizes which connects the gauge to the other tank's sender.

The only other way I can think of is to get a double-pole double-throw lookalike version of your switch (which is a single pole double throw in the arcane language of switches), and I don't know if they even exist. That DPDT switch is basically two of your switches operated by one handle If one did exist, you could connect the "other pole's" wiper to the gauge (the equiv. to terminals 7 and 1 on your switch), and the remaining terminals (equiv to 2 and 4) of that switch to the two senders, respectively. This would be the easiest to implement. Anybody know of a classic-looking DPDT toggle switch?

(PS: are you sure your table is correct? Looks to me like switched power and illumination are reversed between the two gauges. Also, I don't know what is meant by "LOOP L/H FUEL GAUGE".)

Hope this helps.

 

[Dimi Terleckyj]

Hi All

If you need switches, fluid level senders, dash indicator lights etc, just Google
RS Components.
They are one of the largest suppliers of electronic / electrical components around and are excellent to deal with.

I have used them many times both in my business and for my 40 build.
They have a great online catalog

Dimi

 

[Brett James-McCall]

Re: Need help: One Fuel Gauge wiring

(PS: are you sure your table is correct? Looks to me like switched power and illumination are reversed between the two gauges. Also, I don't know what is meant by "LOOP L/H FUEL GAUGE".)

Hope this helps.

Yes, I I better check that tonight... I was just quickly copying cells... teach me to CRTL+X, CRTL+V...

Yes, I am just using standard Smiths Classic gauges and senders.

Not sure Lucas do a DPDT switch, so I may have to try relays. Thanks


Dimi- Yes, thanks, well aware of RS

 

[Seymour Snerd]

Re: Need help: One Fuel Gauge wiring

Not sure Lucas do a DPDT switch, so I may have to try relays.

OK, now this is really brute force, but it might work. Buy somebody else's DPDT switch, and graft the Lucas handle onto it with some careful cutting, drilling, epoxy? (don't hit me). :drunk:

 

[Ian Anderson]

It was actually for this reason I changed my switches over to the metal stalk variety

Ian

 

[Brett James-McCall]

So mulling over some beers this weekend, I thought about this. Can anyone critique it for me?

The idea is to use another relay, a changeover.

Unpowered the relay should sit in one position. When you change the On-On switch, then it powers the relay and latches to the other position and thus picks the other sender.

 

Hi Brett, I did mine it was easy and SGT confirmed I did it correct.
I can e mail a diagram that I did when in work next or Adam at SGT can tell you how to do it.
Simple switching of the live supply to each sender using one fuel gauge.
Dont lose any sleep over thing one !

 

[Seymour Snerd]

Unpowered the relay should sit in one position. When you change the On-On switch, then it powers the relay and latches to the other position and thus picks the other sender.

Looks right to me.

 

[Seymour Snerd]

I kept looking for a Lucas DPDT (for the same reason as Brett, so I can choose which tank is measured) and found this; a headlight switch for an original Mini. In fact, I suspect the headlight switch on my GT40 is the same. So I ordered one. Will report back when I'm sure it would work in this application (pump and gauge selection).

SWITCH LIGHT MKI/II MINI & MINI COOPER S - Classic Mini Cooper