The gauge failure posts cursed my car

There are several formulas for electric current. Volts times amps equals watts? Is that correct? My brother is the electronics specialist in my world. So, in the beginning, the instruments were basic thermal range indicators. They were supplied by a 6-volt system and generator. When 12-volt systems and alternators came along, nearly every mfgr produced a gauge voltage limiter that should make these simple 6-volt range indicators work as close as they did before. A short cut to reworking instruments (GM did re-engineer all of them to 12-volts).
The typical 7805 solid state chip will put out 4.8 to 5.2 volts at switch on and climb to 5.4 or more as it heats up. That is what the adequate heat sink compensates for. Without the heatsink, it wont last long. So the basic instrument voltage limiter that supplied fuel and temp only, plugged in and would live at least 10 years (their goal). For the rally panels with a 3rd gauge (oil pressure) feeding from the limiter, some engineer determined, "nope, it won't survive". So they built a more robust limiter and placed it inside a gauge so the standard limiter could not be applied here. Anyway... If you panel has 2 instruments feeding off 5-volts, They might read a hair low, but close enough for range indicators. Back when I was calibrating OEM rally panel gauges (with oil pressure gauge) to run on the 7805 regulator, every dang one of them had to be adjusted a tad.
Bottom line... if you want more exact instrument readings today, the new instrument will operate on 12-volts and have numbers on its screen.
Due to above post, I must add that 7-volts is too much. The gauges will read a good bit above correct and maybe die sooner. Exactly 6-volts is a correct as they can/will be.
These classics are exactly that. We just deal with it. Good luck to all.