Amp Meter Hook Up

Amp Meter Hook Up

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By Richard - 10 Years Ago

I have a Stewart Warner Amp Meter I want to hook up to my 12 volt system. Near as I can figure the negtative lead goes to the starter motor and the positive lead goes to the generator, but which poll on the gen? Or is there another option.
Thanks,
Richard

By Jimz Bird - 10 Years Ago

Another option to consider in lieu of an Amp Meter is a Volt Meter.
A couple of considerations would be that a VM will better reflect the status of your charging system. Another woud be that an Amp Meter would channel a lot of Amps through wiring that goes into the cockpit.
Here is an idea by MAD Mark Hamilton on how to use a relay with a VM to even better monitor your electrical system.

Also, there is a lot to read on this link but some good thoughts about Amp meters.
http://www.madelectrical.com/electricaltech/amp-gauges.shtml

By lyonroad - 10 Years Ago

Good information. When I started rebuilding my '56 pickup the big yellow wire that went to the ampmeter was welded to all the other adjacent wires. Why there had not been a fire is beyond me.

By paul2748 - 10 Years Ago

As Jimz said, go with a volt meter. As far as I'm concerned, an amp meter inside the car is a fire waiting to happen as evidenced by the reply above.

By dbird - 10 Years Ago

While I wholeheartedly agree with not pulling 8 or 10 gauge wire into the cockpit and running all the current draw through a dash mounted ammeter, I was wondering if there was an affordable automotive unit that used a shunt instead of putting all current through the ammeter. I have a shunt on the boat and also on an old Sears handheld dwell/tach/volt/ammeter, so I know it's not difficult to do.

Don

By kevink1955 - 10 Years Ago

On the 56 Fairlane all the wires needed for an ampmeter are already under the dash on the back of the ignition switch. There are 2 yellow wires, 1 comes from the starter solenoid (it's 12V unfused) the other runs to the voltage regulator (also unfused)
Remove the wire that runs to the solenoid and put it on 1 of the ampmeter terminals then run a 10ga jumper from the other ampmeter terminal to the location on the ignition switch that you removed the yellow wire from. The other yellow that runs to the regulator should remain on the ignition switch

What you have done is insert the ampmeter in series with the battery connection that supplys the vehicle, all discharge and charge current runs thru this yellow wire that you inserted the ampmeter into. If the ampmeter reads backward after doing this just swap the 2 wires on the back of the ampmeter to correct it's polarity.

For the guys who do not want to run high current into the car for a meter, It's already there in the factory harness, as long as your harness is in good condition and any wires you run are protected against chafing I have no problem with an ampmeter, granted a voltmeter can give you almost the same info but I had this SW combo amp/oil gauge from the 60's. A nice rectangle box that fit between the kick panel and the emergency brake and could not resist using it

By pintoplumber - 10 Years Ago

Let me weigh in on this. For me a voltmeter was worthless. I threw a fan belt on my 78 scruby work truck. Heard a noise, checked my gauges, had a needle in the middle of the volt gauge. When I got off the 4 lane and slowed down the truck started boiling over. If I had an ammeter I would have known right away I wasn't charging.

By paul2748 - 10 Years Ago

This is a problem where all you have is a needle, a line and nothing else. If it is a marked gauge, then you can see what the output is as it should drop down to 12 volts rather quickly rather than the 13.5 to 14.5 that it should be running at. At least that is my experience.

By DryLakesRacer - 10 Years Ago

Volt meters came into use when more accessories were beginning to be used especially A/C. An AWG #10 is rated at 30 amps and can easily handle 40 amps for a time which is fine for our 50's cars but today's computer cars need more. As much as we hate them, the "idiot" light is our best friend especially when loosing a fan/generator belt. Good luck....

By miker - 10 Years Ago

I'm more of a fan of voltmeters. Properly marked, they also show over voltage, and having had regulators fail and boil the battery, they let you see that coming.

That said, I've also had shunt type ammeters in marine use, on 90 amp alternators. Not the wimpy auto ones, but units 10" in diameter and 24" long, that make 90 amps all day and don't overheat. No way you run # 2 wire up to the control stations and back.

The other thing we forget in the high tech world is you can still buy fusible links. Smaller wire, non flammable insulation, designed to melt like a fuse. You need to carry spares, and a pair of pliers to crimp, but they save the harness. Find and clear the fault before you replace it. I use those at the alt/gen terminal, from the battery to the fuse panel, headlight feed, and on individual feeds. You can buy "mega circuit breakers" , but a fuse link always works, it's cheap, and it fits in the glove box. For me, it's a must have on an ammeter.

By Jimz Bird - 10 Years Ago

I like Fusible Links also. Especially on the main feed wire to the dash.
Here are some notes on using them.
http://www.madelectrical.com/catalog/fusible-link.shtml
You can also put two fusible links in one ring terminal and have a spare already half wired up. Shrink wrap the end of the spare and it is ready to use. Once the problem that caused the link to blow is found.
Here is a terminal block I like to use. It separates the wires well. This one shows the spare links already in place.

By paul2748 - 10 Years Ago

Not crazy about fusible links either. I've seen pictures of them going up in flames. I'm am old fashioned type of guy - give me a fuse. I used a mega fuse on the cars that I have rewired with an alternator.

By miker - 10 Years Ago

Nice work Jimz. I never thought of wiring in the spare.

Any undersized wire is a "fusible link". The good ones have heavy, hi temp insulation, and won't support combustion. They need to be isolated, as Jinz shows, not inside a harness. I use them in open air, at point of failure. Hopefully, the fuses in the line go before you need them.

For wiring items in general, I've had good luck with waytek. Not cheap, but all the terminals, fuses, loom, etc. I've bought have been high quality.

By The Master Cylinder - 10 Years Ago

pintoplumber (2/10/2015)

That is exactly why I still prefer indicator lights (idiot lights) on charging systems. Throw a belt, light comes on. Simple.

paul2748 (2/13/2015)

I agree, fusible links are not the way to go. I used a 50a Maxi-fuse on the main feed wire.

By DryLakesRacer - 10 Years Ago

I'm glad someone also likes the idiot light. Since I try to keep my car stock appearing I also carry a digital volt meter that plugs into the cigar lighter in the glove compartment. I usually plug it in when driving at night...... Good Luck.....

By Richard - 10 Years Ago

Thanks for all the information. Figure the voltmeter is the way to go and just purchased a SW on eBay. It is colorful with red yellow green then red again for discharge, over charge, and normal. Also has a calibration screw.

By PF Arcand - 10 Years Ago

My 57 car had an Amp meter in an under dash mount when I got it. Later I was advised by a tech to increase the size of the wiring which he said was to light for an amp guage & was contributing to my having problems keeping the battery up, which I did. Quite some time after, I noticed the guage fluctuating badly one day. The guage was an Equis brand & long story short, I discouvered that it was starting to short out, due to the insulators on the back side of it, which had started to melt!.. I've replaced it with a Stewart Warner volt meter off the ignition switch, & the car also still has a Red light hooked up... Most later autos with alternators, don't even have a guage & if they do it's a volt meter.