The headlights work by switching the ground after a relay is turned on. So common is powered, but either low, or high is grounded to select which lights will be powered. The 'blue indicator' light runs off the low beam ground side of the globe wiring so that when the hi beams are switched the low beams are effectively grounded through that light on your dash to make it turn on.
Keep in mind that what stops the low beams fully lighting up is the fact that a better ground is provided through the hi beam so electricity prefers to travel that path being the easier of the two. Only a very small current travels through the blue light and low beam circuit.
Maybe the wiring grounding the low beams is rooted? This wiring would be on your combo switch.
Do the hi beams work when you push the stick forward and when you pull it back. By this i mean without low beams on just pull the stick back, then also try pushing it forward but this time have the low beams on.
Edit: Also check the connectors on the back of the headlights for corrosion. The passenger side one will be more prone to it being located right near the battery.
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