Noob with 73 CT70 K2 w/ K3 wiring (Turn Signals)

Discussion in 'General' started by PJTrail70, Jul 7, 2020.

  1. PJTrail70

    PJTrail70 New Member

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    Ok - I picked up a 73 Trail 70 about a month ago. It was complete and running/functional but I knew I was going to need to do some work. It has a non-OEM carb on it that is larger than stock. It has a larger diameter air inlet and a larger throttle valve. I did a full clean rebuild of the carb and it has been idling and running fine. Which it wouldn't do when I got it.

    The bigger issue and incredibly frustrating has been the electrical. It came with a 6v battery (dead and dry) and rear turn signals. No electrics were working when I got it. The horn wires were cut and the taillight ground was also. At first I didn't realize it didn't need the battery to start so I thought I had loose/broken connections but then realized it doesn't use the battery to start and the battery was in fact dead. Bought a new battery and fixed the broken horn/taillight wires. Then the horn and tail/brake lights were working. Still no headlight or turn signals. Wanting to get this fully functional, I sourced a new headlight (the sealed 6v I assumed was burnt), turn signal flasher and wiring, front TS stalks and blinkers. Plugged everything in and still no go. I have the wiring diagrams and have traced them to confirm they are connected correctly. The wiring harness has a lot of black electrical tape wrapped around it so I thought maybe there's a hidden faulty splice. Bought a new K3 harness (which has the exact same wires/colors as the existing one but no black electrical tape) and installed it. Still no love.

    I have tested the ignition switch and it appears to be getting current at the right places/right times. In the off position, no voltage. In Pos 1, 4.57 voltage at Bat1/Bat2 to E (Ground), In Pos 2, 4.57 voltage at HL/TL to E. It appears that power is getting to the ignition switch.

    I noticed that my stator wiring had 4 wires connected and all went to the stator coils (no neutral switch wire). They were cloth covered (Black, Green, White (maybe yellow), Red). In researching, it appears this stator plate is for either an early KO or a 50 that uses the magneto to run the headlight. The bike came with a spare engine that looked like it had sat in a mud puddle for most of it's life. My son and I were disassembling it to rebuild. It has the correct 3-wire stator and the neutral switch wire (the engine on the bike has the neutral switch but no wire). I swapped over the coils, points, condenser and wired it in. I'm getting spark but no other electrics.

    What am I overlooking? Could the rectifier be causing this? If it's bad it just causes battery to drain, right? Is there a way to test it?
     
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  3. racerx

    racerx Administrator
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    This is a lot to address in a single post. Let's start with some basics, tackling a little bit at a time, in stages.

    First off, the should be a light green/red tr lead coming from the neutral switch. That's apart from the stator itself, just routed into the stator pigtail. Next up, white AC lead for the rectifier; yellow AC lead for the HL circuit. And, finally, a black lead which is the primary ignition output.

    Next up, test the voltage coming from the lighting/charging coil...engine running. Set your multimeter to AC. You should see double-digit voltage from both white & yellow leads, increasing rapidly with rpm. 30VAC would be quite normal, once revs are above 5000.

    Yes, a dead rectifier will cause problems...like no charging and ultimately killing a battery. And, the battery + bulb load are the system voltage regulator. It's referred to as "balanced system". It's crude as it sounds, kinda temperamental...but it does work, if everything is within spec.

    Some testing info...
    The diode can be used as a test lead. You need a 6v bulb and a working battery. Since a diode is, effectively, a one-way/check valve for electrical current, the bulb should only light-up with the diode in one position. IOW, flipping the lead orientation should result in the bulb not being powered, once flipped from the working orientation. Any other result (most commonly the bulb illuminating in both directions) means a failed diode.

    As for testing the rest of the electrical system, on the bike, it's a lot easier to do with having the run the engine. DC power can be fed to both the white & yellow leads, at the harness main connector. Unplug it from the engine, use a known 6v DC power source, connect the ground to the chassis; everything uses a chassis ground.

    The lighting/charging coil is actually two separate coils wound onto a single lamination stack core. Each is grounded at one end, leaving only one output...that can only used be as AC. The diode rectifies AC into (usable) DC, the headlight circuit is fed raw AC, bulbs don't care if they get DC or AC...unlike a battery, or LED.

    That ought to be more than enough to get you started and keep you busy for a while.
     
  4. PJTrail70

    PJTrail70 New Member

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    Thanks for the reply/info Racerx.

    I will head out to the garage and test as you suggested.

    The stator wiring "originally" as the bike came to me had 4 wires all going to the coils/condenser. While the neutral switch was in place in the case it had no wire. The harness side of the pigtail did (does) have the lt green/red wire but the stator side had a red (pink?) wire that connected to the primary coil. I replaced all of the stator components with the spare -- both coils, points, condensor -- and transferred the neutral switch wire over. Now, my stator harness has the 3 wires plus the neutral wire. The harness side of the connector has Yellow, Black, Green wires that go to the stator plus the lt green/red wire for the neutral switch.

    I had assumed that the headlight issue was due to the red//pink wire not connected into the lighting circuit. I had assumed that changing to the 3 wire system would make it correct. I'm also realizing that the headlight will only get voltage with engine running.

    I'm also going to review all of the ground locations as that may be contributing to the other lights not coming on. I have completely rewired my 1971 BMW R75/5 but that is a 12volt system. This 6V system is new to me.
     
  5. PJTrail70

    PJTrail70 New Member

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    OK - update...

    I tested the rectifier as suggested and it tested good. With Bat+ connected to red/white wire and Bat- to Green it showed closed. When I reversed the wires I got continuity.

    Then tried to start bike and no-go. Checked for spark —hmmm. Revisited the points and realized they weren’t opening at all. Adjusted to spec and now I have spark. Started bike and all lights worked. One key exception - when in the “night” position headlight comes on but blinks when TS are actuated (TS do not work with headlight flashing). In “day” position, TS work fine.

    No speedo lights at this point. I’m assuming they are all burned out and need replaced.

    It appears the stator plate from a non-battery system was the issue with the lights. Why would the tail/brake lights previously work without engine running but now require engine running. I thought tail light was separated from the HL. No biggie either way as long as they work while running. Just curious.
     
  6. racerx

    racerx Administrator
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    The key differences between these electrical systems and what is used on most fullsize bike, along with all automotive applications have little to do with voltage. Swap the bulbs, battery & flasher relay for 12v versions and...voila!...the same wiring & switches work with a 12v motor. The list of electrical parts available in 12v flavor is huge and growing; 6v is fading into history. The main issue is that these are split, half-wave, systems. AC is fed the the HL circuit; everything else gets battery power...unless something has been altered. With most other vehicles, the electrical system is full-wave, voltage tightly regulated and everything gets DC from battery power. You can't do that with a CT70 alternator, unless the lighting coil is rewound into a single, ungrounded, (a.k.a. floating ground) coil and a full-wave diode bridge reg/rec unit installed. That's light-years outside the scope of this thread.

    Sounds to me like you've got the battery in the HL circuit...somehow. That yellow HL lead should be connected to the keyswitch only. Seems unlikely, if not difficult, to commingle that circuit with anything else. Only thing that comes to mind is the high-beam indicator lead being mis-wired.

    At this point in the process, I'd unplug the engine from the main harness, run 6v(+) to the yellow & green and test those circuits both independently (yellow only, green only). With yellow only powered, nothing but the HL & high beam indicator should illuminate. With the green powered everything but the HL should work. Any voltage crossing-over between those two circuits means there's short somewhere and I don't necessarily mean an insulation break; it could be something plugged-in where it shouldn't be.
     
  7. PJTrail70

    PJTrail70 New Member

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    Thanks again, Racerx. I'll isolate those circuits and see what happens. Is it possible the "short" is occurring at the primary coil? I've traced (previously) each wire as best as possible prior to attempting the start.

    Here's the wire routing (as I compare to wiring diagram):

    Yellow wire -- stator coil to connector to ignition switch (C). Rest of HL circuit: Br/R wire ignition switch (HL) to 3-wire connector in headlight shell to 1) Dimmer switch (White wire out to HL (lo), Blue out to HL (hi) and Hi Beam indicator light in speedo) and 2) Speedo instrument light in speedo.

    Black wire -- condenser to connector to 1) battery connector (loop) to Ignition coil 2) single wire connector in headlight shell to kill switch

    Green wire -- stator coil to connector to rectifier

    Is the speedo bulb (or wires) a possible source of issue? I have not gone into the speedo to check any of these bulbs/sockets/wires. I have plugged in the wires from the speedo into my harness. After checking the green and yellow wires in the engine harness I may disconnect the speedo wires and see if that has any effect.

    Edit: I should also note that brake light and TS indicators work with key in "Day" position. HL does not. Once running with higher rpm's HL does not flash and indicators work correctly. When started and idling the headlight flashes when indicators are in use but revving engine corrects this. When running in gear all work "correctly".
     
    #6 PJTrail70, Jul 8, 2020
    Last edited: Jul 8, 2020
  8. PJTrail70

    PJTrail70 New Member

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    Final (?) update on electrical issues...

    Tested the Yellow wire and Green wire separately as racerx suggested. Yellow wire behaved as expected -- headlight lit up. Green wire nothing lit up. I put a charger on the battery to ensure it was at full strength. When I returned it still had some wonky behavior. Turn signals would only work with key in "night" position.

    I decided to pull the speedo and have a look at the bulb/sockets/wiring. Wiring all looked correct and clean from what was visible outside the sheathing. The sheathing was quite hard/not pliable but fully intact. The speedo illuminator socket was quite corroded but the other two (High Beam indicator and Neutral indicator) appeared to be in good shape. All three bulbs were toast. I removed the bulbs with the speedo light a bit difficult. Once I removed the bulbs I confirmed voltage was getting to the Hi Beam and speedo sockets. Neutral indicator did not get voltage in either setting.

    I decided to disconnect all speedo wires from the bike and test. Bike functioned properly. HL only came on with power supplied to yellow and all other lights only came on with power supplied to green. I then started plugging the speedo wires back in. I tested after each pair was plugged back in and found no erratic behavior. I started with the High Beam indicator as I felt this was the most likely culprit and then moved to the speedo bulb as it shares a ground connection with the High Beam and I felt the corrosion could have been contributing to the issue. All electrics functioned as supposed to. I then plugged the neutral indicator wires in and still no issue. I had all three bulbs removed (and still do).

    The electrics are functioning as they are intended with the exception of the speedo indicator bulbs which are on order. I will retest when the bulbs arrive to see if problem reappears.

    Could it be the shared ground that is/was contributing to the cross-over between the circuits? Coupled with the corrosion? I kept hoping for an "aha" but it never really came other than 1) The heavy corrosion on the speedo bulb socket and 2) the correct function once the speedo wires were disconnected (and reconnected with bulbs removed). Neither of those were clear-cut "of course" moments though.
     
  9. racerx

    racerx Administrator
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    You did it right. This is the process...trial & error, isolating one change at a time until operation is affected. If there's more than one issue..."lather, rinse repeat", until everything has been sorted.

    The most common issues I've seen over the years are broken leads between the HL shell & frame, bad grounds and rodent damage. Some of the weirdest voltage readings seen were a result of broken leads, in the aforementioned location; those can be damned frustrating when they leads all look fine, externally. It can be a toss-up between unwrapping the harness and bench-testing every lead and just throwing a new, repop, harness at the bike.

    The high-beam indicator light should be connected to high beam lead, coming from the dimmer switch and ground. Since everything is grounded to the chassis, ground location doesn't matter. Yes, corrosion, just like bad leads, can result in seemingly bizarre results.

    The neutral indicator light lead is a switched ground. The (+) lead is part of the horn/brake light circuit. All three of these devices operate the same way...via switched ground & battery power. Side note: this is also why a fuse is important.

    There are a number of places where ground issues can originate with the front end. The speedometer adds more points for electrical resistance, including the mounts, bulb sockets and steering head bearings. Run one lead of your continuity tester to any bare metal spot on the front end, the other end to the frame or engine...there should be continuity, with surprisingly little resistance. Greased steering head bearings conduct low voltage better than seems possible.

    "Aha moments" are reassuring, but don't always happen, especially with electrical problems. My electrical knowledge is based on decades of practical experience and a fair amount of education...but is still limited, nonetheless. For example, the reason why the HL...powered by its own grounded coil...current is affected by battery circuit load, also with its own coil, is above my pay grade. It's just one example of "go by what is known to work and let it go at that".
     
  10. PJTrail70

    PJTrail70 New Member

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    Racerx - I appreciate your continued follow-up. I have chased too many electrical gremlins. The CT70 is relatively easy compared to my full size bikes. Then my bikes are easy compared to all of my german cars...canbus, multiple fusebox locations, and electronics located in leak/spill prone areas...alas, I diverge.

    So, I received the speedo bulbs -- I chose LED replacements -- and installed them one at a time starting with the High Beam one and then moving to the Neutral indicator. I figured if the corrosion on the speedo illum bulb had caused the problem I wanted to confirm all else worked before putting that one in. Without drama, all three lit up at the appropriate times and all electrical systems are now operating at full function. Yeah! Thanks for your help.

    Now, onto the carb...

    Bike is running fine. It seems the idle screw wants to wander at times so every so often it needs to be adjusted. As I indicated earlier the carb is an aftermarket replacement that is larger than the stock one. It has a larger air inlet as well as the throttle slide. I feel like I've dialed it in but the throttle seems to stick and I've noticed two things: 1) the throttle cable casing is aged and cracked -- the PO had put plastic split loom cover on all the wiring/cables except the throttle, 2) the carb slide has what appears to be a rub mark on it which could be causing it to stick. I ordered a reproduction carb when I first bought the bike but was sent the wrong one. The correct replacement was sent but by the time it arrived I was able to clean/tune this one. When the correct repro carb arrived (it was still missing the throttle cable which was supposed to be included) but I also noticed the overall unit was smaller than the one on the bike. The repro slide is a smaller diameter than the one on the bike so a simple swap over is not possible. I'm now gun shy to source the correct slide as I'm not sure how to determine the correct one (or if it even exists as a replacement part). Is it possible/recommended to use emory cloth or extra fine sand paper to smooth the rub spot? Or what other options exist.

    The size of the carb forces the angled cable guide in the slide cap to be right up against the underside of the frame. It doesn't seem to restrict the cable action but there's not much room for error there. Throttle grip assembly seems to be functioning properly. When the throttle sticking occurs the throttle assembly is in the off position.

    Oh and I've removed all of the split loom (it was of the corrugated type) because it looked awful. I replaced both brake cables with correct grey sheathing and replaced the turn signal/horn switch with one with correct grey sheathing. Mine has a combined hi/lo/kill switch which I couldn't find a replacement for but was able to source similar/same grey sheathing. So, with exception of the throttle cable and speedo cable (which is functional and aesthetically fine) all of the controls look good (new).
     

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