Sorry to sound like a dolt but what's the difference between these two types of gauges?

take say an oil pressure gauge. if its mechanical you would have to have a line running to the gauge itself and the pressure would be what moves the needle. with a electrical gauge you would a sending unit that would sense the pressure and send an eclectrical signal the guage to make the needle move.

dsm/mitsubishi service manuals https://www.mediafire.com/folder/5k14qlaulb9s1/dsm_mitsubishi

service manuals(my whole collection) https://www.mediafire.com/folder/ac51jwwa3g1n1/automotive_manuals