Ignition switch voltage vs. voltmeter

I've been using a Ron Francis kit and Classic Instruments guages on my 1929 Ford Hiboy roadster since the early 90s and have been reasonably happy with them. Two years ago, I began to have voltage problems that required two solutions: replacing all battery cables to fix a serious voltage drop, and laboriously cleaning and polishing every terminal. Life was good again.

Two years later, I've observed that the voltage at the ignition switch is 13.4, but the voltmeter reads 12-12.1v. I suspect a grounding problem, but due to the inaccessiblity of the ground connections and my age, I'd like to hear opinions before I do that.

Also, when I turn on the headlights at idle, the voltage drops to just below 12. When I blip the throttle, voltage rises to 12.5 and stays there. In the 30+ years I've had the car, I simply don't recall ever seeing 13v+ on the voltmeter.

What is the condition of the battery, size, age, etc. What size are the battery cables and their length. Age and condition of the alternator. Condition and age of the starter and solenoid.
If this is a small block Chevy all of the above have influence on the charging system.

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Originally Posted by Dorsey

Two years later, I've observed that the voltage at the ignition switch is 13.4, but the voltmeter reads 12-12.1v.

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I remember you chasing the problem two years ago, Dorsey. Ken's questions are good, but what jumped out to me was that you "observed that the voltage at the ignition switch is 13.4V, but the voltmeter reads 12 to 12.1V. How did you observe the 13.4V? What prompted you to start looking at the voltage at different places?

If you are using a column mounted GM switch i have seen them go bad and not make good contact internally. Replaced a bunch of them over the years. Even a regular dash mounted switch can go bad. If you are getting good voltage at the switch but not beyond, I would look there first.