Drop in LED to replace Normal bulbs often perform poorly, especially in old cars. Too many products to say what is good or bad.
Most cheap LED won't last. Poor design, poorly made, or likely both.
Save power? Allot to not much, even no. If you use ballast/load resistors... LEDs plus Resistors can eat more power
then using OE bulbs.
Save Heat? In most cases, Bulb Heat doesn't matter to old cars. UV light from Sun will to more damage then light bulb heat. OEMs know how to deal with heat and most times are very good light fixtures.
Example: Most taillights are in the good to better category, including Fiero, but Fiero Side markers do have heat problems and many front have turned clear from age and UV.
Park or Tail lights use 2-3w each. Taillight fixtures can handle heat makes for years.
Brake/Turn light use more power and generate more heat but most taillights can deal w/ that. Most times Brake/Turn is not on for long each time.
Dim light could be Old bulbs, Dirty Fixtures, Power/Ground problems.
Many old fixtures need cleaning and a coat of fresh spray chrome. Fiero and many others are not totally sealed and moisture/dirt can attack the paint that covers back part of fixtures.
Fiero Taillight ground is hidden under right rear fender and many have rust problem in that area.
See my Cave, Lighbulbs
and LED poisoning
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)