Fuel Gauge Install problem

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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Yonder
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Fuel Gauge Install problem

Post by Yonder » Mon May 09, 2016 12:10 pm

Hi There,
I've just restored a fuel gauge, back to full working condition, using ElwoodJayBlues excellent Sticky here.Many thanks for that EJB... It had broken coil wires, and bad grounding inside. I tested it on a rig I made up using a new tank sender unit. All fine..good Ohm resistance figures..the problem is...My 1944 MB is Positive ground/earth..I know...better ask the PO....All works well on the jeep apart from the present fitted fuel gauge which always goes full deflection. I'd like to fit this repaired gauge, but am worried because she's Positive earth. I don't want to damage the gauge (grounding to the dash is through the case).
Any advice please as to how I can install and use this repaired gauge safely ? (Other than rewire the whole jeep back to original Negative earth) !!! Thanks for any ideas..Richard
RANElliott


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Re: Fuel Gauge Install problem

Post by artificer » Mon May 09, 2016 12:48 pm

Richard wrote:Other than rewire the whole jeep back to original Negative earth
No substantial re-wiring is needed & only about a 1/2 hour's work including re-polarizing the generator.
So go for it!
http://www.classiccarprojectshop.com/20 ... ive-earth/
Grounding of both the gauge & sender unit is essential to obtaining correct readings.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

Yonder
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Re: Fuel Gauge Install problem

Post by Yonder » Thu May 12, 2016 2:31 am

Many thanks John for you reply and the the link for re-polarizing my generator, so that my jeep becomes negative ground. I have read it through, and understand all of it, except for this bit.........

"If you have the older style of coil it is good practice to __replace__ it. By reversing the polarity of the coil you will reduce the voltage to the spark plug by about 50% thus causing a weak spark and all the running issues associated. There is no such issue with the newer style of coil.".......is it because the case is grounded ? Or has it "learned" to operate one way only?.. I do understand that the spark current must flow from the spark plug arm towards the central electrode.

My coil is a Ducellier 6 Volt type with the RUP terminal connected to the distributor. I do understand now how to "flash" the field terminal on the generator to "learn" it to go negative earth/ground.
Finally, am I right in thinking I do not need to touch anything on the voltage current regulator when altering the jeep from POS to NEG ground? John/anyone? Thank you for your help...I don't want to screw up !!..Richard
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Re: Fuel Gauge Install problem

Post by artificer » Thu May 12, 2016 3:18 am

Coil's are designed to suit the polarity of the vehicle's electrical system.
Just get, I am into vehicle's running the best way they can. No F markings or any of that other stuff.

Coils will work hooked up either way, but do best wired correctly.

Understand how ignition coils work:
Coil in feed energizes [creates a strong magnetic field running though primary windings] while current runs through the closed points to ground. PRIMARY CIRCUIT
When the points open, this magnetic field collapses quickly & induces very high current into the secondary coil winding. SECONDARY CIRCUIT. This induced current wants to go to ground to complete the circuit & is what causes a spark to be generated & jump the correct cylinder/s spark plug.

This induced current must go from from the coils centre [king lead] ....across the rotor button....through the spark plug lead/s & jumps the plug gap....all @ the right time.

Reverse the coils input & output leads & things will work, but not quite as well as they should.

Negative earth system....negative coil lead terminal goes to the distributor then through the points to ground.

The condenser stops pitting & arcing of the points by absorbing the excess energy that has nowhere to go, when the points open.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.


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