Depends where your "dim Bulbs" are situated and how they are wired up!
If they are in parallel to another system, they may effect how that system performs downstream from the bulbs.
They can in effect act as a resistor to the power continuing on to the next circuit.
You could throw some 12 volt bulbs into your dashlights, and then find that all the other gauges (oil, temp etc.) read incorrectly whenever the light swich is turned on!
Follow TINY's advice and fit the right part from the start.
