Expert: Ben Deutschman - 5/22/2009

Question
hi there ok i have a 4 headlight system on a 1988 chevy van front end RV..it has the h4656 and h4651..i went to upgrade to the euro diamond lights that take H4 bulbs..i noticed the high beam has 2 prongs and not 3 so i cut off the 3rd prong and stuck it on the high beams..i checked and cleaned all grounds and comnnectors but i get on low beam bright on top but a light glow from the high beams below..when i put on high beam i get bright on high from bottom but not as bright on high beam on the top lights that do the low function ..what gives?? if i should have used a H1 how does one prong go in 2 prong connector? i am so fustrated if it helps i think the old lights did this too and sometimes i have to jiggle one of the low beam connector  to make light come on..

Answer
The reason your old Low/High Beam had 3 Prongs, is that one Prong was a Common Ground, and the other two were 'Hot Leads' for the Low and High Beam Filaments in the Low/High Beam Headlight. If you put two Hot Leads on one terminal of a 2 Prong Headlight, then that terminal will always get power, but it may be shorted when you either try low Beam or High Beam.