I have a 46 Farmall A and I have put a single wire alt on it. I picked up a voltmeter at TSC have a question on the wire hookup. It has two studs on the back (one for positive and one for negative) and I understand that part. The positive stud connects from the wire from the alternator and the negative goes to the starter switch. But it also has a red wire and a white wire on the back of the voltmeter. What are those used for? Do they go to the light switch?
- Thread starter JeremyG
- Start date
charles todd
Well-known Member
With a voltmeter you hook the positive to the ignition coil switched hot and the negative to ground (with a negative ground system). The reason for this is so when you shut off the key it turns off the voltmeter. If you do not have a key, like on a mag system, I suppose you could run it through an oil pressure switch. As for the "other wire" it is probably for a light bulb. It will be obvious if it has a light, it will be a wire out the center of the voltmeter. Wire the light to the headlights or dashlights.
Good luck,
Charles
Good luck,
Charles
Bob M
Well-known Member
A better quality voltmeter draws so little current it can safely be wired permanently "on". Simply wire the voltmeter + to the battery + (or the hot side of the starter switch), and the voltmeter - to a good ground.
To determine resistance take a VOM or DVM and measure the resistance between the voltmeter's + and - terminals. If it's more than about 400 ohms there's no need to switch the voltmeter off with the ignition.
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The red and white wires are most likely for an internal illumination bulb as Charles suggests. If it is and you want the gage to light up, connect the red to the headlight switch and the white to ground.
To determine resistance take a VOM or DVM and measure the resistance between the voltmeter's + and - terminals. If it's more than about 400 ohms there's no need to switch the voltmeter off with the ignition.
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The red and white wires are most likely for an internal illumination bulb as Charles suggests. If it is and you want the gage to light up, connect the red to the headlight switch and the white to ground.
Yo Bob, I just HATE to wire any current drain permanently to a tractor battery regardless even if its only say 12/400 amps which I agree is negligible.
I wonder what the self discharge rate is for a lead acid battery?? If the 12/400 is wayyyyyyyyy less then the batterys own self discharge rate I wouldnt have so much heartburn I dont reckon. I know the electronics in modern cars is always on to say keep the clock time/memory correct but I bet its like near NOTHING, heck a AAA battery would run it for months
Hey remember in school we learned of that "ideal" voltmeter which had a resistance of infinity, where can we get one of those lol, prob the same place we buy perpetual motion machines!!!!!! Isnt it like the first or second or third law of thermodynamics that a perpetual motion machine violates, not to mention conservation of energy n other "stuff" Youre a mechanical engineer you ought to know that !!
Hope to see you again in New York next July but you mentioned some trivial little thing about a daughters wedding JUST whats important anyway?????
John T EE moonlighting as another EE
I wonder what the self discharge rate is for a lead acid battery?? If the 12/400 is wayyyyyyyyy less then the batterys own self discharge rate I wouldnt have so much heartburn I dont reckon. I know the electronics in modern cars is always on to say keep the clock time/memory correct but I bet its like near NOTHING, heck a AAA battery would run it for months
Hey remember in school we learned of that "ideal" voltmeter which had a resistance of infinity, where can we get one of those lol, prob the same place we buy perpetual motion machines!!!!!! Isnt it like the first or second or third law of thermodynamics that a perpetual motion machine violates, not to mention conservation of energy n other "stuff" Youre a mechanical engineer you ought to know that !!
Hope to see you again in New York next July but you mentioned some trivial little thing about a daughters wedding JUST whats important anyway?????
John T EE moonlighting as another EE
Bob M
Well-known Member
John T. I know what you mean about wiring in “permanent current drain” such as a voltmeter. OTOH there’s lots construction equipment, trucks, etc. – including my old Kenworth 10-wheeler – with “always on” voltmeters. As long as the voltmeter has reasonably high impedance (the one in my KW is 1K ohms if memory serves) leaving a voltmeter connected 24/7 represents a much lower current drain than a battery’s self-discharge rate.
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Still hoping to dig out my JD green ball cap and making guest appearance at the NY JD Expo to see you and the delightful Mrs T . Will you be presenting your seminars again this year?
...Bob M
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Still hoping to dig out my JD green ball cap and making guest appearance at the NY JD Expo to see you and the delightful Mrs T . Will you be presenting your seminars again this year?
...Bob M
I guess so, John Jensen requested I come back for more seminars although I only have the same old 3, Charging Systems, Coil Ignition and Wico C and X Mags but its their show so there I will be. Hope to see you, lets put on a dog n pony show at a big IHC show together sometime???
John T [email protected]
John T [email protected]
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