Quick question for you folks with a volt (not amp) meter.  What does your guys' volt gauge read when its sitting off in the garage?  Mine is sitting at a smidge over 12v - is that correct?  It seems lower than I remember, but I could be wrong.

My '78 280 sits just over 12 volts. Probably 13 volts of I had to estimate.

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sounds good - thanks

Mine is closer to 13 but the gauges are not known to be that accurate.  You might want to put a meter on your battery to get an accurate reading.

The gauge is adjustable.  A screw on the back.  Still need an external meter to be sure of the adjustment.

1 hour ago, Zed Head said:

The gauge is adjustable.  A screw on the back.  Still need an external meter to be sure of the adjustment.

That is cool! Didn't know that! I will hook it up to my bench power supply, set a voltage and adjust the voltmeter to match! Cool!

wow, neither did I - very cool

From what I gather there are adjustments on the back of all the gauges - ducks for cover as he awaits being corrected, without mercy or compassion! I will be messing with the Rev counter soon as it’s about 10% optimistic across the range. The 123 ignition while cruising tells me this; and I’m more inclined to believe it than a 40+ year old analogue gauge.

 

Back on topic, I was quite surprised to find that what I considered very small variations in standing voltage at room temperature show a dramatic difference in the state of charge / the health of the battery. The AGM battery used in my Audi with stop/start, I always felt was no longer at it’s best and you can watch the voltage drop quite quickly as you stop at the lights - yet it does start the car on the coldest of winter days. With the engine off she holds 12.3-12.2v, which to me says for the stop/star to work as intended, she needs replacing- see chart below.

 

So my advice is disconnect the battery, check voltage when not cold or hot as well as checking the calibration of your gauge.

 

My Z gauge shows a standing voltage of 12.5ish - but then again the battery is two years old, is disconnected ( using the battery isolator) every time the car is not in use and lives in a heated garage.

 

 

 

 

 

One thing to keep in mind is there is significant parallax error when viewing the gauge since it's over there on the side and you're not looking at it square.

I find mine "accurate when viewed from the driving position", but if I look at it "straight on", my battery voltage appears to be low. I've decided that since I'm most often looking at it from the driving position, I'm going to keep it that way.

Makes me wonder if maybe they calibrated them like that on purpose.

Maybe someone should modify the voltage meter to put a mirror behind the needle to address the parallax error. ?

I like my amp meter. :)

upgrade to a amp meter :)

I love that word upgrade, I hear it so often when talking about old cars.

Or should that be an ammeter!? :p

Sorry - pedant mode off now!