71- z 50 Head light goes out when I hit the brakes .

TENACIOUS T · Oct 31, 2018

I've had this problem for a long time and the back story is - had the engine rebuilt 5 years ago by a vintage Honda shop that's been in around for 40 years . When he had it torn down he said the coils were in bad shape and he had some used that he could replace with . So the lights never worked right after I got it back . I even took it back after I restored it and he worked on it for 2 hours and charged me another $200. So I started looking at it again and he put the coils and wiring out of a 68 - 69 ( with Battery ) . So I ordered and replaced with the parts for a 71 ( no battery ) . So what I have now is - key on , starts and runs great , all 3 - brake switches light the brake light nice and bright . Switch the key for lights - head light works - high and low beam and tail light works . But if I hit any of the 3 brakes - the head light goes out and the tail light / stop light go dim . I triple checked the wire connectors in the head light and still can not find it . T

69ST · Oct 31, 2018

The battery-less Z50s are beyond finicky in terms of electrical load. Too much and the bulbs will produce a dim orange, too little and you'll be buying bulbs by the gross. That TL bulb draws more current than you may realize, ~23W with both filaments in the circuit, i.e. brake & TL powered. The original HL bulb was 15W/15W...anything could be in there, at this late date. The lack of a battery makes the system highly unstable...and complicates diagnoses. Could be something as simple as improper bulb wattage (combined), a bad ground, a shorted lead or a switch problem.

First step, unplug the stator pigtail from the wire harness, then feed 6V from a known power source (such as a battery, or transformer) then run the lighting system through its paces. A healthy 6V battery can easily support 40W+, for a short time. If that "cures" the problem (and it may) then you know where to look...either lower wattage bulbs, or the addition of a battery. If not, you know where to come for help.

kirrbby · Oct 31, 2018

Was the bike repainted? Do you have a clean, metal to metal connection (ground) where the taillight bracket bolts to the frame?

Does it do it at high rpm too, or only at idle? Higher rpm equals more power being generated by the coil. K2 lighting isn't great, even when everything is in good tic.

TENACIOUS T · Oct 31, 2018

I did have a problem with grounds at the key switch - had to scrape some fresh paint off . With a DMM set to buzz I get good grounds on any thing I touch - head light bucket - any bolt - fender . So should I get a buzz when I touch ground then the brown wire ? Because I do and that does not seam right to me!

69ST · Oct 31, 2018

On the CT70s of this era, brown was dedicated tail light power, from the keyswitch. Green/yellow brake light power, via the brake switches...which was fed via the red lead (that also feeds the horn) marked "BATT" on the keyswitch. The tail light base, itself, had a ground strap. If your z is wired this way, then there very well may be a short in the brown lead.

Might be time to remove the harness, for unwrapping and inspection on the bench. I didn't want to jump into this level of diagnosis, right from the get-go. So...before taking that step, verify that the brown lead is correctly connected, circuit-wise, and it hasn't been spliced by a P.O. There could just as easily be mis-positioned pin at the main wire harness/keyswitch plug and that's a lot easier than open-harness surgery. Disconnect the keyswitch from the harness, if the problem persists, time to dig into the harness.

TENACIOUS T · Oct 31, 2018

So I checked the HL bulb and it is a 6v 15/15w . What I see on the wiring Dig. - brown wire feeds HL and TL . Next I used a 6v car battery and unplugged the connector @ the key switch and ran 6v to the brown wire - HL and TL lit nice and bright on high and low / but had no way to work the brake light ?

69ST · Oct 31, 2018

Here's a generic Z50A schematic. I'm hoping that this is the correct one for your bike. It should pretty well explain how things are supposed to work.

Tripod · Oct 31, 2018

^ these guys are great at diagnosing, just follow their lead.

Im kind of confused, you have a k2 z50 Then you added a battery? Did you put in a lighting coil and wiring for a k1? Are you using a k2 keyswitch?

TENACIOUS T · Oct 31, 2018

So racerX that diagram isn't even close to a 71 - z50, k2 and just makes things more confusing . Tripod - no no the 40 year expert put the wrong stator coils in ( 68-69 that uses a battery ) when he rebuilt the engine . I'm trying to make it all original and the lights work correct again .

allenp42 · Oct 31, 2018

I'm no expert either on hard tails Z50's, but found a wiring diagram of a 71. Also, I think the stator used in 71 is the same, or very similar to the stator used on many soft tails. It appears that a 71 uses every winding in the lighting coil, which is different than soft tails. I would check the plug wiring to make sure it is correct. I would wager a bet that if the windings don't supply the correct circuit, you will get some crazy results.

allenp42 · Oct 31, 2018

Found a little additional info. Depending on your skills and how good a DVM you have, here are the resistance values of each winding in the lighting coil. I made these a few years ago and will gladly double check, if needed.

Note: All measurements to ground
Red – 1.1 Ω
Blue – 0.5 Ω
Gray – 0.3 Ω

TENACIOUS T · Nov 1, 2018

The coils , generator , stator , call them what you will are new - Stator repair kit - part number SKU 165 from CHP . So it might be they are not up to the task ? Has any one else used this stator repair kit with luck ? I'll check the wires with my DMM .

allenp42 · Nov 1, 2018

I have never used CHP's coils or any aftermarket coil for that matter. Part of me thinks it should work because they've been selling them for a long time. Here's another tidbit that you find helpful and probably worth a peek since your bike has already been worked on by someone other than yourself. When your key switch is in pos I, the gray wire from the stator supplies power to the TL. In Pos II, the headlight turns on and the blue wire is connected in parallel with the grey wire to supply a little more "oomph" for the TL. So basically, the red wire supplies power to HL and the Grey & Blue power the TL.

An easy check is to make sure the wire colors align on both sides of the side plug ...just to make sure that nothing got swapped.

It may be that the AFT parts are not up the task, or something has changed (or incorrect) between the stator, key switch, etc. If this is the case, even a NOS Honda lighting coil may not fix your problem.

kirrbby · Nov 1, 2018

K2 Z50's are wired differently than everything else. Early softails use the same stator I think, and no battery in the system, but the lighting is different.

Here is a K2 diagram from a K2 manual.

I'll add a pic of a K1 Z in a little bit...for comparison.

kirrbby · Nov 1, 2018

K1

TENACIOUS T · Nov 1, 2018

First off allenp42 - that is the correct wiring diagram on post #11and #14 . I checked the resistance and have Red = .3 Blue = .3 Green = .7 Black = 0 . Add one more thing - to cheat the system the 40 year expert took the white wire ( you see next to the main connector ) and stuck the bullet end into the red wire (@ the main connector ) to power the brake lights . I removed that and plugged it back into the white bullet connector after install of the new stator repair kit .

hrc200x · Nov 1, 2018

Believe k1 to k2 z50 ignition switches are different from eachother so make sure you have a k2 switch.

allenp42 · Nov 1, 2018

I think your meter is a little stingy, which is not at all uncommon. Just so I can have a frame of reference, please stick a piece of paper in-between the points and recheck the black wire.

I hate to ask you to do this, but please recheck the resistance for the red, blue, green. Red should have the highest resistance of the 3 leads on the lighting coil, but less than the black wire on the pri coil.

allenp42 · Nov 1, 2018

Also, please make sure the stator plug is disconnected from the main wiring harness when you make the check.

69ST · Nov 1, 2018

TENACIOUS T said:
I did have a problem with grounds at the key switch - had to scrape some fresh paint off . With a DMM set to buzz I get good grounds on any thing I touch - head light bucket - any bolt - fender . So should I get a buzz when I touch ground then the brown wire ? Because I do and that does not seam right to me!

Continuity between a power lead (in this case, the brown TL +) and ground, with no switch closed = short.

71- z 50 Head light goes out when I hit the brakes .

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