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  • light show

    Need suggestions on things to check. My headlight is going on and off while riding at night. Not good. It especially gets erratic when I hit a bump. The bike has completely been gone through. All electrical connections have been cleaned and all grounds have also been cleaned. I am running an aftermarket led headlight. It is a JW Speaker 8790 Adaptive 2. It is an 81LH that I am having the problem with. The handlebar controls have all been rebuilt/resoldered. I was wondering if anyone has ever experienced this. I was going to throw parts at it but would rather start with the things that maybe someone else has seen. I will be checking for loose connections today. Thanks for any input.
    2 - 80 LGs bought one new
    81 LH
    02 FXSTB Nighttrain
    Jim

  • #2
    I would suspect the LED lamp, easy enough to check if you have another headlight from one of your other Specials. If it works fine with the replacement light, you could eliminate wiring and switch/relay issues.
    2H7 (79)
    3H3

    Comment


    • #3
      Originally posted by bikerphil View Post
      I would suspect the LED lamp, easy enough to check if you have another headlight from one of your other Specials. If it works fine with the replacement light, you could eliminate wiring and switch/relay issues.
      The lamp is high quality American made and is brand new. Easy enough to swap out from one of my other bikes. I have three all with the same new led headlights. I am thinking it has to be a loose connection because of it acting up when I hit bumps.
      2 - 80 LGs bought one new
      81 LH
      02 FXSTB Nighttrain
      Jim

      Comment


      • #4
        The loose connection could be a cold solder joint in the new headlamp! I also think you should swap it out for another and test. If two of the "new" headlamps do that, then put in the oem style lamp and try that.
        Ray Matteis
        KE6NHG
        XS1100 E '78 (winter project)
        XS1100 SF Bob Jones worked on it!

        Comment


        • #5
          Update and another question. Been raining quite a bit down here in Mississippi and I don't like to ride in wet conditions so it took a while to test things as I had to wait until night time to see the headlight. Anyway, I swapped the headlight with another one from one of my other bikes. The headlight did not go on and off like the other one did but I have another issue that I need electrical gurus to chime in on. While going down the road at about 70 I noticed that my tach would go from about 5k to 0. As it did that I noticed that my dash lights would dim when the tach dropped and brighten back up when it went back to 5K. My question is .... Is this just the well known tach problem or am I possibly having other issues. The RegRect. is charging correctly and the battery is reading 13.3 volts at rest. Hope everyone is enjoying the 4th today.
          2 - 80 LGs bought one new
          81 LH
          02 FXSTB Nighttrain
          Jim

          Comment


          • #6
            I have the same problem on my SG. As the RPM approaches 5k, the tach becomes erratic.

            I have tried two other tachs, and the problem persists.

            You might know that the tach gets it's signal directly from the alternator output.

            I suspect I have an break inside the wire between the 3 wire alternator connector and the tach headlamp connector. It seems like 5k RPM might excite some resonance to make the problem appear at 5k RPM.

            I haven't been ale to track it down yet. Rather lazy considering it's been 4-5 years!
            -Mike
            _________
            '79 XS1100SF 20k miles
            '80 XS1100SG 42k miles
            '81 XS1100H Venturer 35k miles
            '79 XS750SF 20k miles
            '85 Honda V65 Magna ~7k miles
            '84 Honda V65 Magna 48k miles (parts bike)
            '86 Yamaha VMAX 7k miles

            Previous: '68 Motoguzzi 600cc + '79 XS750SF 22k miles +'84 Honda V65

            Comment


            • #7
              Yes I was researching the alternator right after I wrote the last message. I am going to go through the checks in the wires behind the fuse box. I think I might have a spare winding.. Can't remember for sure... but I do have three midnight specials. I could always swap it from one of the other bikes just to see if that is the problem. It is a weird problem and may be what was causing my original light show with the other headlight. I also was looking a the write up concerning tach wobble but going back and forth from 5k to 0 and back with the tach and speedometer lights dimming and brightening has to be something going on with the alternator. i checked the voltage reg/rect. and it is putting out well over 14 volts with the engine revved up. I guess these issues are what makes them fun to own.
              Last edited by cajun31; 07-05-2021, 12:52 AM.
              2 - 80 LGs bought one new
              81 LH
              02 FXSTB Nighttrain
              Jim

              Comment


              • #8
                Well, looking at the 80-81 wiring diagram, the white wire from the alternator that provides signal to the tach is also the same white wire that triggers the headlight relay. As you may know, this wire has a latching diode inline to keep the headlight on in case the engine stalls. These diodes usually fail/disintegrate preventing the headlight relay from triggering. Possibly this may be a warning sign it is about to fail and is causing interference when a higher voltage (5K RPM) is thrown at it. May be something to check/replace or you could eliminate it completely and bypass the headlight relay for testing purposes. I have never heard of this on the 78-79 bikes, but guess what... no inline diode on those bikes.
                2H7 (79)
                3H3

                Comment


                • #9
                  I was having an issue with my original LG and headlight a couple of years ago ... Ended up being the relay under the tank. Replace it and everything was fine. I solved the issue by working my way from the RLU through a new diode to the headlight relay. Process of elimination finally arriving at the relay. Bought a few used ones off of EBay. The moral of this whole story is I actually bought 3 new diodes from Partzilla. they came fully ready to plug into the wiring harness. So I can easily replace that. Biggest problem is getting to it on this bike.
                  2 - 80 LGs bought one new
                  81 LH
                  02 FXSTB Nighttrain
                  Jim

                  Comment


                  • #10
                    Just a shot in the dark. I think if the headlight relay were just unplugged, there would be no current going thru that diode to interfere..Then see if the problem persists with the tach/lights. The headlight can function by jumping the red/yel and the blu/blk at the relay harness plug. That way the relay and the diode would be out of the equation.
                    2H7 (79)
                    3H3

                    Comment


                    • #11
                      Originally posted by bikerphil View Post
                      Just a shot in the dark. I think if the headlight relay were just unplugged, there would be no current going thru that diode to interfere..Then see if the problem persists with the tach/lights. The headlight can function by jumping the red/yel and the blu/blk at the relay harness plug. That way the relay and the diode would be out of the equation.
                      Nice tip... I may try that. Thanks.
                      2 - 80 LGs bought one new
                      81 LH
                      02 FXSTB Nighttrain
                      Jim

                      Comment


                      • #12
                        Problem solved. I tested all the wiring from the alternator through the wires in back of the main fuse back up to under the tank. Everything checked out OK. I then put a battery tender volt meter on my battery tender leads and checked the battery with the bike sitting off and the battery was in good shape. I then started the bike and revved it up enough to watch the increase in voltage on the meter. It climbed quickly up to 14.7 volts then 15.5 then 16.8 until the meter flatlined. Bad voltage regulator rectifier. Fortunately I had another bike sitting nearby with the seat and tank already off an 80LG. Swapped that RR on the bike having the problems. Tested again and it held steady at 14.7 volts revving the bike. Put the tank and seat back on and took out for a 10 mile ride. Tach is now working flawlessly. My next thing to do is to put the original headlight back on the bike and take it for a ride on a bumpy rode to see if the headlight works ok. I also need to do some research on those JW Speaker lights to see if they have some kind of fail safe built into them to keep them from burning out when hit with too much voltage. Hopefully I have not ruined that light.
                        2 - 80 LGs bought one new
                        81 LH
                        02 FXSTB Nighttrain
                        Jim

                        Comment


                        • #13
                          Originally posted by cajun31 View Post
                          Problem solved.
                          Great to hear, I always like it when people come back and let the forum know what fixed the issue.

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                          • #14
                            Great you got it figured out.
                            ​​​​
                            2H7 (79)
                            3H3

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                            • #15
                              Hopefully the last update on my light show problem. As I stated previously the Voltage R/R was bad. Replaced it with a good one. I researched my JW Speaker Adaptive 2 headlight and indeed the bad R/R was the reason for the light going on and off. There are and I gather in most quality LED headlights ... protection circuits built into them. Of course the radical fluctuations of voltage coming out of the bad R/R was what was causing the light to basically protect itself by cutting itself off. I have also researched another possible fix for the light going out. I found a conversation on another motorcycle forum where someone was describing having the very same problem with his light going on and off at higher rpms. He found these and stated it resolved his problem. Amazon.com: Xprite LED Headlight Canbus Anti-Flicker Harness| Bulbs Resistor Decoder Error Free Conversion Kit for H4 (1 Pair): Automotive. Someone had told him to check to make sure the Voltage regulator was not putting out too much voltage at higher rpms. So it seems that by finding and replacing my bad R/R has resolved all of my issues.
                              2 - 80 LGs bought one new
                              81 LH
                              02 FXSTB Nighttrain
                              Jim

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