Voltmeter vs. Idiot light

JasonNC

While installing my Autowire Wiring harness, I am trying to replace the idiot light with a S&W voltmeter and I'm not sure if I'm doing it right.  Currently I simply have a ground wire going to the negative post on gauge and a wire to an accessory wire from fusebox going to positive terminal.  I expected the indicator marker to move to show some voltage when I switched the ignition on.  So far, nothing but I really didn't have the ground wire connected to a good ground.  Regardless of the ground issue, I'm wondering if I should run a wire straight from the alternator to the positive terminal of the gauge since that was essentially the way the idiot wire was connected.  

RichardD

Jason, I run a voltmeter and the 'idiot' light. The light is for INSTANT knowledge; and the voltmeter is for a more informed knowledge !! Just connect the "+" on meter to a 'switched' connection under the dash {more convenient than going thru the firewall again}; probably the heater fan switch supply that is probably above the gage if you mount below the dash on the left side like I did. Use a 'ice pick' tester to check a supply by operating the ignition switch on and off. You want the gauge to register only when the ign. is turned on.
You should get around 14 volts with the car running and around 12 when it is not. If you have a digital gage to test across the battery you can usually set the SW gage in the rear if it is not showing exactly that number. With a voltmeter you can see if your alternator can put out enough to charge the battery while you are running with everything on. If it drops to 12 volts when i.e. you are running air cond., radiator fan, and 200 watts of halogen lights and 200 watts of driving lights, etc etc and the voltage goes up when you cut the a/c off: you do not have a strong enough alternator and you can't drive across the state at night like that; the battery would die. Perhaps not a good analogy but the voltmeter is much better for diagnostics in old cars. You need the light also to give you a warning since you can't look down below the dash all the time while driving. Connect the gage light to the lighting switch { or to the '+' on the gage if you want the light on all the time while running}.
Keep having fun with the nice car.