Transistor in rally gauge ?

I don't believe I would have solved a few dilemmas with my car without the help of this clan. You guys simply...rock. If that is the term.
I seem to need a helping hand again. I have been told there is some transistor (maybe there is another term) that allow the guages to work properly.
Can someone advise me where I can buy one from.
Again, in advance thanks for all the help.
MAPS