low beam not working, headlight mod

[tjhess74]

i was at a friends house over the weekend, and as i rode up to his place, he said i had a headlight out. the low beam on the h4 bulb was out, but the h7 was still on. we took the bulb out and it looked fine. put another bulb in and same issue.

the fuses were fine and his multimeter showed 12v to the wire supplying power to the h4 low beam. however, a test light wouldnt light up, conflicting the multi meter read out.

the previous owner did the mod, and i havent really investigated which version he used. all i know is this:

h7 is on the left side, h4 is on the right. a wire is running out of the harness on the left side (just behind the steering stem) and runs over to the right side bulb. this is the wire supplying power to the h4 low beam.

i havent had anymore time to look at it, but does anyone have any ideas? im not an electrical engineer, so basic is good for me.

 

[chaskell27]

Sounds like you have probably already done this but I would start with the obvious stuff. Check to make sure the connection are all tight, both at the headlight and at the harness. Beyond that, if you are showing power in the wire up until the headlight connection, you've definitely got it narrowed down to that area. Good luck

 

[tjhess74]

the connection is solid, i just cant figure out why the multimeter would show voltage, but the test light wont (and yes, it works. tried it on the high beam). dunno, ill have to dig into it some more this weekend. itll be a good chance to see how he did the mod.

 

[chaskell27]

Sorry I can't be more help on this one. It's tough without seeing it. It's always fun digging into the bike and finding the stupid things that previous owners did to them huh??? Good luck and let us know what you find out.

 

[tjhess74]

lol, that is a very true statement chaskell! i should know the drill by now...buy a used bike, tear it down, fix it right, then ride it...:thumbup:

 

[Motogiro]

i was at a friends house over the weekend, and as i rode up to his place, he said i had a headlight out. the low beam on the h4 bulb was out, but the h7 was still on. we took the bulb out and it looked fine. put another bulb in and same issue.

the fuses were fine and his multimeter showed 12v to the wire supplying power to the h4 low beam. however, a test light wouldnt light up, conflicting the multi meter read out.

the previous owner did the mod, and i havent really investigated which version he used. all i know is this:

h7 is on the left side, h4 is on the right. a wire is running out of the harness on the left side (just behind the steering stem) and runs over to the right side bulb. this is the wire supplying power to the h4 low beam.

i havent had anymore time to look at it, but does anyone have any ideas? im not an electrical engineer, so basic is good for me.

Your volt meter may register voltage at extremely low current that will not be enough to light even a small incandescent lamp. See attached plug diagram for the H4 lamp. One common lead and a high beam signal and low beam signal. The low beam signal is turned off as the high beam signal is turns on. This is achieved using a relay that is controlled by the ECU. The ECU keeps the low beam off until the engine starts. This helps the battery devote current to the starter and other circuits during starting. The ECU also gets a signal through the high beam indicator in your instrument cluster. This tells the ECU to turn off the low beam signal through the dimmer relay since the low beam is not used while the high beam is active.
Is your high beam indicator lit? If some one jumped a signal to the high beam circuit then the ECU sees that the high beam is active and unloads the the dimmer relay and stops current to the low beam. Look at the schematic. Dimmer relay is #60. High beam indicator is #35. Low and High beams are #61 and #62. Hope this helps!

 

[tjhess74]

no my highbeam indicator is not on. the system has worked fine until this (usually the way it is right?!) the h4 plug is set up as it is in the diagram.

when using the multi meter, he grounded using the bulb connectors ground, and the low side only showed power when the high beam was off.

ill just need to take the inner fairing off and start tracing the wire to see where current picks back up. its just strange that it would stop working all the sudden...no bumps, bruises, or rooting around.

 

[wlaroche]

i was at a friends house over the weekend, and as i rode up to his place, he said i had a headlight out. the low beam on the h4 bulb was out, but the h7 was still on. we took the bulb out and it looked fine. put another bulb in and same issue.

the fuses were fine and his multimeter showed 12v to the wire supplying power to the h4 low beam. however, a test light wouldnt light up, conflicting the multi meter read out.

the previous owner did the mod, and i havent really investigated which version he used. all i know is this:

h7 is on the left side, h4 is on the right. a wire is running out of the harness on the left side (just behind the steering stem) and runs over to the right side bulb. this is the wire supplying power to the h4 low beam.

i havent had anymore time to look at it, but does anyone have any ideas? im not an electrical engineer, so basic is good for me.

I am thinking that the wire gauge might of been to small to handle the current needed to supply the power for the low beam. Maybe the wire just finally melted through and it cannot handle the current any more. Check the resistance of the wire and/or replace the wire with a larger gauge. I dont remember what size wire I used for this. For some reason 16ga sits in my head.

 

[Drinky]

just to the bd43 mod, that works great

 

[tjhess74]

ok, its fixed. i found some time to get into it. i found out why the multimeter worked and the testlight didnt...when the power was applied to the bulb, it was too much for the connection at the harness and would ground out. resetting the ignition and unplugging the bulb would put power back to the wire. sometimes the connection was bad enough that the test light would trip the circuit. wiggling the wire at the harness connection would make it flicker.

sooo, long story short, i took off the old crimp connector and 2 miles of electrical tape, and put on a posi tap coated with liquid electrical tape. when it dries ill wrap it back up and put it back together. it works like a charm now. cheers to previous owners...:Flip:

thanks for all who put in thier suggestions!

EDIT to add...their is a green wire in the harness on the left side of the frame. this is the one the previous owner tapped into. i havent read any of the headlight mod threads (as this mod was already done) so i assume this is the correct (or a correct) wire. i might dig into some of those threads and see where others have powered the low beam.