Seaside Pete Posted April 21, 2015 Report Share Posted April 21, 2015 Hi guys I am just about to fit my new tank, and my system has been changed to 12v neg earth by the previous owner, but he has removed the live feed to the fuel gauge. I know I have to fit a resistor to drop from 12v to 6v. I have shown below 2 pics of A: the back of the fuel gauge as it is at the moment and B: a wiring diagram. My questions are first there seems to be some kind of resistor fitted already but as I do not have any pictures to compare I am not sure what it is, is this the same as fitted to all P15's as original equipment or has it been added? The 2nd pic is the existing wiring (shown as the solid line) could I not feed the gauge (as per the dotted wiring) instead of going via the starter button as shown in the manual? Also is it critical what wire goes where at the sender end? Sorry about not having a perfect pic of the back of the gauge but it was a bit difficult to get the camera in position. Thanks in advance. Pete Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted April 21, 2015 Report Share Posted April 21, 2015 not a resistor..that is a noise suppressor for the gauge built in voltage regulator as it operates....yes it is important what wires go. on the tank and the gauge both will be marked 1 and 2 or A and B..... 1 to 1, 2 to 2 etc...the way it works is the resistance is divided by the wiper and each leg pulls the gauge in opposite direction ...that is why the gauge is slow acting and rock steady even with sloshing fuel in the tank. Quote Link to comment Share on other sites More sharing options...
Seaside Pete Posted April 21, 2015 Author Report Share Posted April 21, 2015 Thanks Plymouthy. What about the live feed, could I wire it as I have suggested? Plus as I can't quite see it is there a terminal under that noise suppressor where I connect the live feed? and as it is now neg earth instead of pos does it need to be wired different? Sorry for so many questions. Thanks Pete Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted April 21, 2015 Report Share Posted April 21, 2015 number one ..you have drawn the thermo model fuel sender/gauge..so you will have the three wires...there will be a stud among the mix somewhere marked BATT or B...this is you common voltage in..the guage has a built ion 5 VDC regulator that is bi-metal operation..this suppressor eliminates RF to the radio....it will be on the input to the gauge and will ground by the terminal clamp/other radial wire...as long as you have your battery supply on the switched side of the ignition you should be good... IF you do not have three wires on the gauge..you could well have the 49 very late P15 wiring utilized as with the new to be P18...the tip off would be also a single post sender at the tank...look close to the tank..post of two and marked as I stated earlier...be ye aware that a good ground is needed...suggest an aux ground wire for GP and over all good feeling... NOW I CANNOT EXPRESS THIS ENOUGH...as you have the car and it could well have been altered and you now trying to get it all working...verify both the gauge and sender for proper matching system... Quote Link to comment Share on other sites More sharing options...
Seaside Pete Posted April 22, 2015 Author Report Share Posted April 22, 2015 (edited) Thanks for that. There are already 2 wires connected at the tank sender that go straight to the 2 wired posts on the gauge as pictured, there are no other wires going to the gauge only that suppressor as seen. As I am not going to use the radio I think I will remove the suppressor and connect the live feed as per my drawing direct from the ign switch (live after switching on) via a fuse and resistor. Any idea what size fuse? Thanks Pete Edited April 22, 2015 by Seaside Pete 1 Quote Link to comment Share on other sites More sharing options...
ssdave Posted January 6, 2016 Report Share Posted January 6, 2016 not a resistor..that is a noise suppressor for the gauge built in voltage regulator as it operates....yes it is important what wires go. on the tank and the gauge both will be marked 1 and 2 or A and B..... 1 to 1, 2 to 2 etc...the way it works is the resistance is divided by the wiper and each leg pulls the gauge in opposite direction ...that is why the gauge is slow acting and rock steady even with sloshing fuel in the tank. Found this thread about the "noise suppressor" on back of fuel gauge. Anyone know where to get one? Mine is broken. Thanks Quote Link to comment Share on other sites More sharing options...
ssdave Posted January 7, 2016 Report Share Posted January 7, 2016 Found this thread about the "noise suppressor" on back of fuel gauge. Anyone know where to get one? Mine is broken. It's the brown "card" with the small canister attached in the first picture at the top of this page. Any help greatly appreciated. Quote Link to comment Share on other sites More sharing options...
dale Posted January 8, 2016 Report Share Posted January 8, 2016 12V to 6V resistor you need for dash gauges are on E-bay for about a couple dollars each. On the fuel gauge the 6 volts goes on the center post and the two wires from the tank sender go on the outside posts. If you get the sender wires mixed up the gauge will just work backwards. Make SURE the sender unit is well grounded. Cherrio Quote Link to comment Share on other sites More sharing options...
ssdave Posted January 8, 2016 Report Share Posted January 8, 2016 12V to 6V resistor you need for dash gauges are on E-bay for about a couple dollars each. On the fuel gauge the 6 volts goes on the center post and the two wires from the tank sender go on the outside posts. If you get the sender wires mixed up the gauge will just work backwards. Make SURE the sender unit is well grounded. Cherrio That's a resistor on back of fuel gauge? This car was not 12 volt ( will be soon tho) Plymouthy called it a "noise resistor" the whole piece that the canister is mounted to is what I need. Haven't seen it at any of the parts suppliers Quote Link to comment Share on other sites More sharing options...
ptwothree Posted January 8, 2016 Report Share Posted January 8, 2016 (edited) 12V to 6V resistor you need for dash gauges are on E-bay for about a couple dollars each. Actually, it is a voltage regulator. They will provide a steady voltage to the gauge, eliminating fluctuations from voltage rise or loss from the charging system. I have one of these running both fuel and temp gauges in my '64 brand X car. Replaces the old style mechanical regulators used to reduce 12v down to 5v. I used one LM 7805. An LM 7806 would provide 6v for a 12 to 6v conversion or just to have a steady 6v feed for the fuel gauge. Around $2-3 ea. Edited January 8, 2016 by ptwothree Quote Link to comment Share on other sites More sharing options...
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