Have you checked the ground for a poor connection or high resistance?
Here is a video showing how to do it on a 2003 S-10.
This bolt is exposed to the elements and apparently is pretty common to turn both lights on.
You want to measure resistance by setting your meter to ohms and putting a lead on the eyelet and one on the negative battery post. You should have less than a half ohm.
https://youtu.be/7s4xOxi0EOo
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Tuesday, June 4th, 2019 AT 7:28 PM