Z1-B Electrical head scratcher

Folks, I'm in a bind. I built my 1975 Z1-B out of parts, a bare frame from Ebay in Australia, top and bottom engine cases from Ebay USA, and just about everything else from Ebay, FB Gumtree (Like Craigslist) etc. It all went together really well. All of the electrical components apart from the OEM battery box, gauges, headlight, tail light etc are good quality repros. While I was waiting for a few engine parts to arrive I hooked up the wiring (wiring harness is a new repro from Z1 Parts) and had everything working fine. Lights, blinkers, horn etc.

I finished work on the engine and fired it up with no problems. I originally went with no rear fender, but changed my mind and installed one, along with a nice OEM tail light to replace the aftermarket one I'd originally bought for it. When I'd installed the rear fender and tail light I couldn't get the tail light or brake light to work. That was weird, because I tested the tail light and bulb beore installing them, and even the 47 year old bulb still worked fine? 

I used my old test light to check that I had power going to the lights and I had, but they weren't on? Weird. For some reason I hooked the test light up to the black and yellow ground wires, and discovered that I have power going to the ground wire as well, so it appears that I have power coming from both the ground wire and the power wire? Same/same with the flasher unit (brown/orange) wires, It's not blowing the main fuse, it's just confusing all of the electrics so that the only thing that seems to work is the ignition (I installed a Dyna 2000 and only used the hotwire for power to the coils, ignition pickups and black box, and used the Dyna's ground wire direct to the negative terminal on the battery) and the horn.

The lights don't work, the electric starter doesn't work, the blinkers don't work. I've disconnected every electrical connector I can see and made sure that I've connected everything correctly, I've tried unplugging each multi-connector to see if that made any difference, there's no bare wires rubbing on the frame, not that the thick powdercoat would allow anything to short out on it anyway, probably. The handlebar switches are new and worked fine until now and I have new ones in a box for my next build so I might swap them out and see if that makes any difference, but if it doesn't, I'm not sure what to do next, I'm wondering if anyone else has had the same issue, and how you fixed it? Thanks in advance.    

Z1 Friday 28 Jan 2022 3 by Terry Prendergast , on Flickr

Hi Terry,
+ starts at the battery and goes to solenoid, a white wire is spliced into the battery cable and goes to fuse.
- starts at battery and bolts to engine on right  side, a black/yellow is spliced which feeds the harness.
Check red wire on + battery terminal, check red cable and white wire have continuity, I've had two fail and now connect white wire to solenoid to avoid this problem.
Check black wire on - terminal of battery, check for clean case when ground bolts to engine, check for continuity between black wire and black/yellow wire.
Check for 12 volts using white wire and black/yellow wire.
I am 69cb750 on cb750 board.
 

Terry take the bulb out, do. you still have voltage on the earth wire? I suspect not. When you have voltage on the earth side of the consumer it is because there is a resistance or open circuit in the earth line. If you have a voltmeter connect it between battery positive and the earth connection of the lamp. If there is more than 0.5v difference to the battery voltage you have a bad earth. Happy hunting

There is a fault finding guide in the FAQ section that I posted which may help you

Just wondering if your ground wire from battery to the engine is OK?  There may also be a ground wire coming off the solenoid that goes to the engine ground point.  Some Z1B's have it and some run the wire through the solenoid connector.  I've had both types.

Your ground wire is bad if you see power on the ground side when the switch is on.
Make sure all of your frame grounds are clean of powdercoating.
I can run you through more tests if you need it.
 

wrote:

Terry take the bulb out, do. you still have voltage on the earth wire? I suspect not. When you have voltage on the earth side of the consumer it is because there is a resistance or open circuit in the earth line. If you have a voltmeter connect it between battery positive and the earth connection of the lamp. If there is more than 0.5v difference to the battery voltage you have a bad earth. Happy hunting

Thanks mate, sorry I didn't reply right away, it was my 40th wedding anniversary yesterday so I wasn't allowed outside to play with my bikes. Today I removed the tail light bulb, turned the ignition on, connected my test light to the earth wire and turned the light switch on, and sadly, it still has power. I then removed a bulb from the right rear blinker, and same/same. Bugger. Buuuut..... Following your directions further, when I connected my voltmeter across the new Motobatt battery's terminals I saw 12.87 volts.

I then touched the + connector to the + terminal on the battery, and the - connector to the black/yellow connector, turned the ignition on, put the right blinker on, and the reading dropped to 1.92 volts! Same/same when I put the lights on/touched the brake lever/ brake pedal. I touched the negative connector to my frame earth point, and it went straight back up to 12.87 volts! Interesting! I then touched the negative terminal to the rear fender, and only got 3.6 volts. Aha!  

Aha! (again....) So, I remembered that I had some trepidation when I ran the old crusty OEM wiring thru the little tunnel under the rear fender that maybe, just maybe, a power wire to the tail light might just touch and short the wire out? Tomorrow I'll remove the tail light and disconnect the wiring, and see if there are any breaks in the insulation to see if it's creating a short somewhere? All of this came to pass when I was installing the fender, so things are definitely pointing in that direction, but if you or anyone else has any other suggestions, I'm all ears! (eyes?) Thanks again! 

Hi TerryThis definately looks like a earth problem (you are loosing 11v, if this was a positive short you would blow a fuse of have a fire to put out)  when looking for a fault that effects multiple consumers you need to look for the common denominator (in this case the ground) looking at the wiring diagram all of these systems come back to a single earth point I am sure the guys on here that are intimate with the Z1  will be able to tell you exactly where this is - Don't get hung up un the fact that you have a positive reading on the earth line, this  simply means there is another resistance in the earth circuit for the voltage to overcome before it diminishes to approx 0v when it returns to the battery negative terminal (in this case a significant one if it is holding 11v in reserve to overcome it !)  

The PDF doesn't seem to work (403 when trying to open) try this

typically there are two grounding points. The negative battery cable grounds the the upper engine case at the rear upper engine mount on the right hand side of the engine. The other is a black wire off the stater harness, off the relay bracket blue connector, that solid black wire is typically grounded to the chassis at the seat lock attachment bolt. 

Thanks Mikaw, I suspect the one by the seat lock is the issue since the problem seems to have started following fitting the rear fender   

wrote:

Thanks Mikaw, I suspect the one by the seat lock is the issue since the problem seems to have started following fitting the rear fender 

 

Thanks guys, as I said in my first post I built this bike from parts, so not knowing where the battery cable was meant to be attached I sanded the powdercoat off the frame adjacent the seat lock, then ran another (smaller gauge) wire from the battery's negative terminal to a bolt on the cam cover. Tomorrow I'll change them around as they should be, and see if it fixes it.