You were actually initially right, I searched for that actual part and it is indeed a bimetallic strip along with a heater (that turns off when the strip moves away from a contact) and not a device with a solenoid/relay.
Apparently whatever it supplies is tolerant of that sort of interruptions in its power source -- I imagine that it would operate on a quite lower frequency than a "vibrator"-type power supply where magnetic force moves the contacts (and elasticity returns them).
I read about this probably 10 years ago, my memory was clearly a bit faulty on it. I didn't want to take the device on my Dodge apart just to verify it :-).
The thing is, the instruments require the noisy 5V.
You can buy kits with an electronic 5V source, and also to replace the old guts of the instruments with modern ones. That retains the original look, with modern accuracy and performance.
You were actually initially right, I searched for that actual part and it is indeed a bimetallic strip along with a heater (that turns off when the strip moves away from a contact) and not a device with a solenoid/relay.
Apparently whatever it supplies is tolerant of that sort of interruptions in its power source -- I imagine that it would operate on a quite lower frequency than a "vibrator"-type power supply where magnetic force moves the contacts (and elasticity returns them).