I just had a similar problem. No bright lights. Replacement harness had a 3 pin plug connector from the dimmer switch. Power/high/low. Traced the problem to this. Pulled it apart and found the pins inside the connectors were not making contact for the high beams. Pushed pins in farther on both halves of connector to be the same as the other two. Plugged it back together and now they work fine. Might not hurt to look.
Good luck,
Jeff
"Do not walk behind me, for I may not lead. Do not walk ahead of me, for I may not follow. Do not walk beside me either. Just leave me alone, you're starting to freak me out."
1957 GMC 150
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