Topic: Why does my Frame and Engine show 12 Volts?

[NWSteve]

Putting together a K3 engine with a K1 frame - engine and wiring harness  from a K3.  After installation and initial success with lights and horn, everything stopped working and there was 12 volts gong to the engine and frame.  Disconnected everything on the harness and we still had the short.  Turning off power to the voltage regulator stopped the short, but none of the previously working lights, horn etc worked.  We decded the wiring harness was faulty and bought a new one.  After installing the new harness, we have the exact same symptoms.  Another oddity is that we have to disconnect the battery overnight to be able to successfully get some of the system working.  Any ideas for diagnostic steps would be appreciated.

NWSteve

[BenelliSEI]

Tried a different battery?

[HondaMan]

The 750K1 grounds the main harness ground underneath the seat. The K3 started out that way but became a ground-at-the-coils version partway thru the build. That's one possibility.

Another is: do you have the battery ground lug in between the frame the the top-left-rear engine mount, and is the frame and engine cleaned of paint there? It should not be grounded anywhere else on the 750. I have sometimes seen them painted over (powercoated frames) to the point of non-contact: the paint on both parts must be removed and the lug trapped in between: the frame geometry actually provides 1mm of space there for the lug when the other engine bolts are all tightened first.

[NWSteve]

Thanks for the responses.  Will check the frame grounds and let you know if it's successful.

NWSteve

[calj737]

I wonder if you have the field coil connected incorrectly and are powering it constantly directly from the battery and draining it and it is transferring that current to the frame through the motor hangar bolts?

[Bodi]

Hmm. If you measure from the battery "-" to the frame and engine, and read battery voltage, that means the battery negative is not connecting to the frame and engine. There really isn't any other explanation. A few things like ignition coils, field coil, various lights, all get power from the battery but ground to the engine or frame. So if the connection from frame to battery is no good, you'll read battery voltage from battery neg to the engine and frame through all those things.
If you connect a jumper from battery neg to the frame, it shouldn't short and melt the jumper - just power up the stuff that's on.
The negative cable to the frame is pretty large and if something is shorting out, the harness wire will melt and burn without that ground cable even warming up noticeably.

[NWSteve]

Really appreciate the information - I am going to re-rasp the frame ground spots and i've also ordered the solid state regulator/resistor replacement.

Thanks!

[jgger]

Correct me if I'm wrong ( that happens often). But if you touch the positive lead of the tester to the positive post of the battery and the negative to the engine or frame, isn't that the same as touching the positive and negative posts on the battery with the tester?

[scottly]

Yes, if the battery negative post is actually grounded to the frame.

[Deltarider]

In general. A good ground contact (aka earth) is often overlooked. Corrosion can play a role. When a frame has been powdercoated, it's a must you connect the battery minus cable to an unpainted part of the frame.

[MauiK3]

I've also seen the battery main leads corrode up inside the insulation which affects conductivity. It can be hard to see but the insulation gets a bit bulgy.

[BenelliSEI]

Curious what solved this. A new battery?

[NWSteve]

Appreciate all the constructive info.  The resolution of our issue was indeed that we did not have a good, consistant ground to the frame at the engine mount point.  Our frame was powder-coated and we were sure that we had rasped sufficiently to bare metal at that part, but, after going back and exposing a better bare connction - everything worked as expected!  Thanks again for the help.