Another option is to go digital. Stack a couple of
these, one above the other, next to the existing voltmeter, and use the old voltmeter's cutout for another gauge. Leave the idiot lights alone.
I plan to do this one of these days. I'll look for a red gauge, though, for the sake of night vision. Blue is terrible for night vision.
But then, if you dare put a digital gauge in one of these old classics, you'll be guilty of sacrilege and will be asked to reflect and take stock of yourself and consider what you are doing.
EDIT: Putting the gauge details here, as links sometimes go bad.
SMAKN® Blue 0.28" Mini 2 Wire DC Voltmeter 2.50~30v Digital Display Voltmeter Gauge LED Voltage Detector
Product Description
Cutting size:23.5mm x 10mm
Mounting holes distance:29mm
Measuring range
C 2.50~30V Two-wire access
Measurement precision:0.01V(3-10V); 0.1V (10-30V)
Refresh Rate?about 500mS/times
Display:Three 0.28 " LED digital tube
Display Color:blue
Operating Temperature:-10 °c ~ +65 °c
Power supply same Source,self-Power
Current consumption: generally 5-15mA, less than 20mA
Reversal protection:Have
Wiring: Red: Power Supply +,Measure Voltage +,(2.50~ 30V DC)
Black: Power Supply -, Measure Voltage -
If measure 10V below, accurate to 0.01V,display x.xx
If measure 10V or more,accurate to 0.1V,display xx.x