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58 FLEETSIDE 04-25-2013 03:08 PM

Amp gauge
1958 Chevy Fleetside with original gauge cluster with 350 sbc, one wire 100 amp alternator, HEI distributer and electric motor fan. When the electric motor fan kicks on it would send the amp gauge from the middle of the gauge to the far right. This let me know my fan was on and that my alternator was putting out current. I rewired the entire truck with an EZ Wire kit and have either overlooked it or it did not come with a wire for the amp gauge. The amp gauge has several connectors on the back of it and I don't know what wires it takes to get it going again,,,,,, any suggestions?

malc 04-25-2013 03:13 PM
AMP gauges at the dash are troublesome.
They should be by-passed, and then install a VOLT gauge.

Wether or not you agree itīs worth reading.

poncho62 04-25-2013 03:44 PM

Trouble with an amp gauge is that all the cars current must go through it to get a proper reading. That means taking a main wire through the amp gauge.....A volt meter just monitors the voltage, so a feed from almost anywhere will tell you your charging system is working....I would just install a voltmeter if I were you.

Rick 5150 69 04-25-2013 03:58 PM

You may be able to buy a volt meter to match the panel from Classic gauges...
1958 Chevy Apache Classic Instruments Gauge Cluster Install - Custom Classic Trucks Magazine

41 Buick custom 04-25-2013 04:46 PM

Amp gauge
There are diagrams to show you how to wire it up. Amp gauges we're in cars for a lot of years. If they weren't safe the factory wouldn't have used them. You have full power going in to run your fuse box anyway. All a amp gauge is a big fuse with a shunt in I, draw to many amps and it will shut down.

75gmck25 04-25-2013 07:46 PM

Full current amp gauges were fairly common in older vehicles, but the output of alternators was also usually quite low (about 40 amps or less). As alternator amperage increased, the in-dash amp gauges were changed to a shunt-type amp gauge, which does not flow the full current through the wiring.

An amp gauge that uses a shunt under the hood (used by GM in the 70's) works more like a milli-voltmeter that measures the voltage drop between two points in the wiring harness. The gauge then uses the measurement of voltage drop to calculate an amp (or current flow) reading on the gauge. Its similar to measuring the amount of fuel in your gas tank at two points in time. If you know the amount of time and the fuel level difference between the two measurements, you can calculate the fuel flow rate.

The article referenced in a previous post by Rick 5150 69 identifies a replacement cluster that uses a voltmeter instead of an ammeter. This is a much safer choice.


vicrod 04-25-2013 10:04 PM

ohms law
There is no question that the voltmeter is the gauge of choice as compared with the ammeter.
Some of the statements here on the HRBB about ammeters, however, are incorrect. Including Madelectrical.
While it is correct that some Manufactures (Chrysler) did route the full electrical load (current) through the ammeter, GM did not. Don't know about Ford. Who cares.
All the data I have seen indicate that GM used the main accessory wire as a shunt and measured the voltage drop (IR) across this wire to drive the ammeter. It's ohms law stuff.


ogre 04-26-2013 02:01 PM

i did a write up on how to change an amp meter to a volt gauge in a task force truck over on the 67-72 truck forum
i have a build thread over there look for post 36

i used the stock gauge face and inserted the guts from a 2'' volt gauge into the stock cluster
here the truk is off and voltage is zero, i installed the needle to be on the middle dot when the voltage is 14 volts

ogre 04-26-2013 02:05 PM

here the truck is running down the road and the gauge is reading 14 volts at the center dot
lots of good 55-59 chevy truck builds over on the site you should be over there too :D

vicrod 04-26-2013 07:44 PM

no no
Are taking pictures at 100 mph? :spank:

snkbyt 04-26-2013 10:02 PM


Originally Posted by Rick 5150 69 (Post 1670234)
You may be able to buy a volt meter to match the panel from Classic gauges...
1958 Chevy Apache Classic Instruments Gauge Cluster Install - Custom Classic Trucks Magazine

Exactly!!! get rid of the AMP gauge... notice NO new cars have one. Used to be that if the AMP gauge blew you were stuck. Get a volt meter that can connect to anything with voltage. AMP gauges are things of the past...:)

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