jagman Posted March 4 Report Share Posted March 4 I have an interesting problem. Using low beams I have two of the four lights as O X O X , when I switch to high beams I get X O X X , where O is on. I have checked for 12 volts at the switch and have it there. I have switched the relay with no change. My dash light for high beams / head lights does not work either. I am getting only 6.5 volts at the low beam lights. According to the manual there should be a ground wire from the headlamp relay but I can't find where it goes to the frame. Any help would be very welcome. Quote Link to comment
Stoffregen Motorsports Posted March 4 Report Share Posted March 4 Sounds like a textbook case of bad grounds. Quote Link to comment
datzenmike Posted March 4 Report Share Posted March 4 Headlights have power to all when headlight switch is on. HI and LOW are selected by the relay to ground. If ANY work then the ground is working. You're getting 6.5 v at the low beam lights because the 12v is going through the filament first. Right side only for now. Unplug the outermost bulb on the right side (the low beam) Measure the resistance from the left terminal as viewed from the rear to the top center terminal and then to the far right terminal. I suspect there is no resistance on the center terminal because the filament is burned out. Replace the outer low beam lamp. Left side. Get access to the rear side bulb plugs on the left side. Probably from behind the radiator support? First make sure there are two wires to the innermost bulb and three wires to the outermost bulb and that the plugs are not installed upside down. Center terminal should be at top. If good continue... Measure the Red/Blue wires on the left side plugs, it should be 12v or battery. If yes... Make a ground wire and touch the Red/Yellow wire on the left side plugs... the outermost low beam should light up. If not the filament is burned out, replace. Now ground the Red wire and HIGH beams on both lamps should light. Anything that does not light is likely burned out. Replace. Quote Link to comment
banzai510(hainz) Posted March 4 Report Share Posted March 4 (edited) I say corrossion at a connector or connector relay somewhere swap in spare lamp from behind Edited March 4 by banzai510(hainz) 1 Quote Link to comment
datzenmike Posted March 4 Report Share Posted March 4 A blown bulb or a blown filament that has flopped onto the second filament and welded itself to it. Low beams O X........ X O High beams O O........ O O O X....... O X this is impossible. I see no way that a high beam can be on when on low beams are on. And why I asked for more information. Quote Link to comment
Thomas Perkins Posted March 4 Report Share Posted March 4 (edited) Also check your red wire fusible link.Mine burnt at the connection a few years back.It melted the white connector their and the wires couldn't make connection.I trimmed the melted part off with my box cutter and it fixed it. Edited March 4 by Thomas Perkins Quote Link to comment
powderfinger Posted March 6 Report Share Posted March 6 On 3/4/2024 at 5:42 PM, datzenmike said: O X....... O X this is impossible. I see no way that a high beam can be on when on low beams are on. And why I asked for more information. Yep, seems like the drivers side bulbs are in the wrong position somehow. Not sure the wiring harness has enough play to allow for that though. Quote Link to comment
datzenmike Posted March 6 Report Share Posted March 6 It should. Two wires for the inside bulb and three for the outside ones. Quote Link to comment
jagman Posted March 6 Author Report Share Posted March 6 I followed your advice Mike and I am replacing all the bulbs. Thanks Dim and None! Steve Quote Link to comment
datzenmike Posted March 6 Report Share Posted March 6 They are likely old and halogen actually dim with age. Was the harness reversed? Quote Link to comment
jagman Posted March 7 Author Report Share Posted March 7 All the harness checked out. I had 12 volts to the fuses, 12 volts to the switch, new bulbs, changed out the relay and the right side came on. Flipped to high beam and two lights died but one on left came on. Started over from the battery checking wire and connections. saw a fuse holder on the red wire and promptly broke the fuse pulling it apart. Replaced it with a 15 amp mini and reconnected the wire to battery. I charged the battery turned on the lights high and low beams. I have no idea what the fix was. The wiring loom is original as far as I can tell. THE GREAT UNKNOWN has bekond. Thanks Mike Steve 1 Quote Link to comment
datzenmike Posted March 8 Report Share Posted March 8 I don't think there are any in line fuses in the headlight circuits. They are all relay and fusible link to reduce the chances of the lights going out suddenly. Was this fuse near the battery positive terminal??? Quote Link to comment
NC85ST Posted March 8 Report Share Posted March 8 Could you post a picture of what you’re talking about, the fuse you changed? Quote Link to comment
banzai510(hainz) Posted March 8 Report Share Posted March 8 If fuse broke apart then that was it.due to age or just weak connections inside ,if typical glass fuse.weak solder joint.vibration /corrossio Quote Link to comment
NC85ST Posted March 8 Report Share Posted March 8 On a 720, it shouldn’t be a glass fuse. Quote Link to comment
datzenmike Posted March 8 Report Share Posted March 8 I'm assuming a fusible link (red) blew and someone spliced a regular fuse back in Quote Link to comment
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