Don't worry you're not going mad or senile.... you've been given the wrong part number!
501 comes up as a 5v indicator/repeater bulb because that's what it is -the correct part number for the instrument panel is 286
You need 9 for the main 3 clock dash plus one each for whatever 52mm dials you have.
Does the length of the LED fit into the instrument?
I have put in new bulbs and it is much better lit than before.
Edited by Alpenflitzer, 10 January 2016 - 02:04 PM.