I have a 2000 Saturn SL2 automatic, with approximately 240,000 miles on the odometer. Had it since 2011, when it had 121,000 miles. Great car.
Recently I updated all of the headlights and the fog lights to LED bulbs. Vastly improves night vision. However, the fog light pattern has
become diffused from the original pattern, but much brighter.

After converting the headlights to LEDs I noticed that the daylight running light feature disappeared. At first, I thought that I had
failed to reconnect the bulbs. After investigating, I found out that there are NO separate daylight running light bulbs. Rather, a plug-in on the under
hood fuse panel reduces the voltage to the low beam bulbs, which were, of course incandescent halogen bulbs.

Well, LED bulbs will NOT operate at a lowered voltage. Hence, no daylight running lights. I left the plug-in in place.

A small price to pay for the vastly improved vision at night!

 

Another problem that can happen is that some LED replacement bulbs run at full brightness on 6 volts in some applications. 2000s Ford trucks run their LED swapped daytime running lights at full power. This is extremely irritating since they are the bright light function, blinding opposing drivers. We eliminate the resistor that provides the daytime function on LED converted trucks. Better at night but no daytime running light benefits during the day.

 

That plug in is a relay which puts the high beam bulbs in series so they operate at 6V. So you could put the old bulbs back in for the DRLs and still have LEDs for the low beams.

 

Not all LEDS are created equal.
Check out bulbfacts.com for lots of good information