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I would like to replace my 1968's battery gauge with a volt meter. Does anyone have instructions on how to do the wiring on this? Can I use any of the currently existing wires (going to the battery gauge) or do I need to run totally new wires?
Any help is appreciated!!!
Also identify the old ammeter wires as to 'which one went to which terminal'. That will make it a LOT easier to reconnect, if a future owner wants to return it to stock state.
Not really sure why you want to change it. The ammeter CAN tell you more about the charging system....if you know how to read it properly.
Last edited by 7T1vette; Aug 29, 2019 at 08:48 AM.
^ It seems to me the ammeters are very often non functional and burned out in many of these cars... I know the one in my 74 is dead and I am going to upgrade to a volt meter myself simply to be able to see if my alternator is working correctly and check battery voltage. If ammeters were superior It begs the question as to why they were replaced as time went on in vehicles including corvettes, with volt meters?
Also identify the old ammeter wires as to 'which one went to which terminal'. That will make it a LOT easier to reconnect, if a future owner wants to return it to stock state.
Not really sure why you want to change it. The ammeter CAN tell you more about the charging system....if you know how to read it properly.
Unless you cut the wires off the connector- the ammeter only connects one way....
Both ammeter wires come from the same length of wire in the main power harness. But, they are separated by about 18", which means the resistance of the wire between them can be used as a current shunt. The voltage drop across that length of wire can be fed to the "ammeter" to approximate the current flowing in that line. So, yes, either wire can be used to provide voltage reading for a voltmeter.
Me, I like to run wires directly from the battery positive and ground to the gauge, so I know EXACTLY what voltage the battery is seeing... Often times, you'll get significant voltage drops across the oem harness, which can give you false (low) readings at the voltmeter. Is this important? Not really..... I'm just OCD as hell so... I want to KNOW what the battery is getting.. I have a lot of electrical stuff on my car so I really keep tabs on the charging system.
Example:
When hot, I may see 14.0-14.2v at the alternator post. Reading voltage at the battery will usually be 13.7-13.8v... Reading voltage on the cigarette lighter wire, 13.2v...and I'm sure voltage drops on the oem gauge wiring are even worse....
However, all that really matters is that you know its charging and the battery is seeing at least "13 something".
The most important is where the alternator "sees" the voltage-
If you want to jump up the voltage up from the alternator -you just fool the regulator into thinking the alternator output voltage is say 0.6 volts lower than it really is, then the regulator will adjust the output voltage to 0.6 volts higher than this. GM did this to get away on the cheap by running smaller wire...Say the alternator is charging at 13.8 volts, it'll will increase the output voltage to 14.4 volts. You can just put a diode in a series with the voltage sense input right at the plug - it''l drop the about ½ volt and you'll now have more voltage!!!
Me personally- I like the voltmeter switched on with the ignition....AND it's on when you are starting the car if you use the pink "ignition" wire
7T1vette,
You asked why I am changing it...
I am changing it because my ammeter no longer works properly and I have no idea how to make it work properly. I had to upgrade to a much larger alternator when I installed a Vintage Air A/C. To keep from frying my old wiring, I increased the size of the alternator wire and moved it from the horn relay to the starter. That caused the ammeter to only read in the negative and to never show a charge. To save myself a lot of headaches trying to figure out how to rewire the ammeter, I decided to simplify matters and replace it with a voltmeter.
Get in touch with Roger at Corvette Instrument Service. He should be able to hook you up. Unfortunately, he does not have faces for my ‘75 so I am looking at aftermarket gauges.
Battery Meter to Volt Meter Conversion
