Headlight Conversion To H4 Bulbs

[lambrkt]

Hi all you out there with 4 headlight 4 x 6 (165mm) systems which is most Chev/GMC 1981 - 1988 trucks, blazers, burbs and most probably 1989 - 1991 units with 150mm horizontal light systems here is some info. to save you (unlike me) a long frustrating afternoon . I purchased a conversion pair of headlights which use replaceable H4 (also is GE9003 etc.) bulbs, supposedly much cheaper than a 2A1 type sealed low beam, $9 vs $23. I wanted to leave my 1A1 high beams in place and run the conversion units as low beams since they get more use and burn out sooner. Should be 'plug and play' right? Wrong! When I connected them up, I discovered that the high beams were coming on very dim when only the lows should have been running. I am running a relay style harness from LMC and I thought the high beam relay was stuck on. Put my old wiring back; same problem. Checked the high/low beam column switch out - not the problem. Went to the store and bought an H4 bulb, disconnected both low beam units and plugged the bare bub into the three prong upper socket - problem with high beams coming on dim recreated. Clearly the H4's leak current to the high side if you use the stock wiring connections. H4's are dual filament and here is where the trouble starts.

 

How to fix. After some research on the internet in other forums I discovered that the stock low beam 2A1's viewed from the back, clockwise from left terminal are Ground, Low - right terminal, High - bottom terminal. H4's when viewed from the back with the top tang oriented up and the two side tangs oriented down, the way they fit into the conversion light, are Ground - left terminal, Low - top, Hi - right terminal. On my drivers' side low beam connector I interchanged the low and high beam wires. These are colored brown and green on my Burb. Problem fixed until I interchanged them on the passenger side plug. So, next I left the passenger side brown wire where I had moved it to and interchanged the black ground and the green high. Problem fixed.