Amp gauge Question
Thread Starter
|
Senior User
Joined: Mar 2001
Posts: 108
Likes: 0
Amp gauge Question
I am helping my buddy wire his 72 F250 4x4. He bought a painless wireing kit. Got everything but the amp gauge working. The kit has the + wire coming from the alt to the fuse box and then another wire going to the solonoid. The instructions say to connect the amp gauge in series from the wire going back to the selonoid. I do this and the gauge pegs out when running. I was told I need a shunt wire to drop the voltage to the gauge. I have his old wireing harness and tried to find this wire, but non of the wires change voltage on the ohm meter. Question is what am I looking for and how do I make it work? I found a wire that went to the selonoid originaly and about three inches down it has a rectangle box, is this the Shunt wire? If you need any more info let me know.
Thanks
Chad
Thanks
Chad
Posting Guru
Joined: Jun 1999
Posts: 2,415
Likes: 3
From: Comox Valley, Canada
Amp gauge Question
The shunt should be a larger black wire with a red stripe. The ammeter should go in parallel with the shunt. If you put it in series the least that will happen is the ammeter pegs, usually it fries 
Sparky
Sparky
Thread Starter
|
Senior User
Joined: Mar 2001
Posts: 108
Likes: 0
Amp gauge Question
[updated:LAST EDITED ON 12-Feb-02 AT 06:15 PM (EST)]So I don't mess it up please explain how to put it parallel. And do you know what the resistance of that wire would be?
Thanks
Chad
Thanks
Chad
Posting Guru
Joined: Jun 1999
Posts: 2,415
Likes: 3
From: Comox Valley, Canada
Amp gauge Question
There are ammeters that are designed to be installed in series, large power wire from alternator to one side of the ammeter and another large power wire from the other side of the ammeter to the fuse box. But these are a very old style for a vehicle and havent been used for quite some time. The entire current draw of the truck goes thru the ammeter. So if the ammeter dies so does the truck power system.
The newer types are actually millivoltmeters, useless trivia
The shunt/ or shunt wire is hooked between the alternator + wire and the + wire to the fusebox, in series. Meaning one end of the shunt is hooked to the alternator wire and the other is hooked to the fusebox feed. The ammeter has one wire to one end of the shunt and another to the other end of the shunt, this is parellel. This way the current flow for the entire truck doesnt flow thru the ammeter. This is a more modern design. The size of the shunt will vary for each ammeter, sorry I dont know what size you would need. Possibly you can find out from a place that sells vehicle ammeters.
I hope this makes sense.
Sparky
The newer types are actually millivoltmeters, useless trivia
The shunt/ or shunt wire is hooked between the alternator + wire and the + wire to the fusebox, in series. Meaning one end of the shunt is hooked to the alternator wire and the other is hooked to the fusebox feed. The ammeter has one wire to one end of the shunt and another to the other end of the shunt, this is parellel. This way the current flow for the entire truck doesnt flow thru the ammeter. This is a more modern design. The size of the shunt will vary for each ammeter, sorry I dont know what size you would need. Possibly you can find out from a place that sells vehicle ammeters.I hope this makes sense.
Sparky
Moderator
Joined: Jan 2001
Posts: 56,966
Likes: 2,728
From: Virginia
Amp gauge Question
All of the aftermarket amp guages hook like the instructions tell you with the wiring kit. You must be trying to hook the factory guage up. Find that shunt in the old harness. I am curious as to what it really looks like myself.
Thread Starter
|
Senior User
Joined: Mar 2001
Posts: 108
Likes: 0
Amp gauge Question
Thanks for the help. Another question though. Looking at the diagram, being electricity follows lowest resistance, wouldn't the current actually flow around the shunt though the gauge? Shouldn't the shunt be on one end of the gauge and then back to the the power wire, but keeping the power wire strait though? This, I would think, would let the current flow normally from the fuse box on, but a lower current to the gauge. Could be wrong, thats why I am here.
Thanks
Chad
Thanks
Chad
Trending Topics
Posting Guru
Joined: Jun 1999
Posts: 2,415
Likes: 3
From: Comox Valley, Canada
Amp gauge Question
The shunt actually has a very low resistance, lower than the ammeter. The ammeter is measuring the voltage drop across a resistor (which in this case is the shunt), and the voltage drop is in the millivolt range.
Sparky
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Moderator
Joined: Jan 2001
Posts: 56,966
Likes: 2,728
From: Virginia
Amp gauge Question
Yea, think of electricity as water flowing in the pipe. The wire going to the shunt is a very large pipe. The shunt is a undersized piece of pipe inserted in the large pipe going to the solenoid. This undersized pipe (shunt) will build a little pressure up (voltage). The more water passing through the undersized pipe (shunt) the more pressure will build up (voltage). The factory ammeter is a very very small pipe with hardly no flow to it. It is measuring the pressure difference across the undersized pipe(shunt). Even though the shunt is a restriction, it is much larger than the ammeter wires and circuit itself.
I don't know if any of the above makes sense.
I don't know if any of the above makes sense.
