Tricky charging system problem

[ilmod]

I have 1975 CB750F that I have restored (father bought it new in 75) Everything is going well except the solid state rectifier I put in is putting 16.5v to the battery at 4k rpms. Had the rect/reg checked and it is good. The input to the regulator (black wire) is about 1.5 - 2v less than battery voltage so regulator is maxing out voltage to battery thinking a low voltage state. See youtuibe video here: https://youtu.be/6S-aYG9H6rY Here's the situation;

-new battery
-alternator, rotor, stater, field coil all check good. Took them to Honda stealership for bench test. (see pics)
-new ignition coils
-cleaned and re-seated all connections
-bypassed ignition switch with jumpers, no change
-resistance from black wire on regulator to positive battery lead (disconnected from battery) .3 ohms
-removed headlight, no change
-the ignition coils take about .5 ohms load with key on engine off (seems right)
-key on engine off- 12.8v at battery / 11.2 at regulator input
-removed head fuse, very little change engine running (about .3 volt difference)
-removed tail fuse, almost a volt difference. Almost seems to be right but still gets 15v to battery at 4k rpms (should be 14.5v)

So something is loading down the switched side of the 12v circuit and causing the regulator to think low voltage state always. I'm told there should be max .5v difference between battery and regulator input.

ANY ideas are welcome!!!! Thanx

[TOOLS1]

I have never heard of a SOHC stator going bad. My first thought is the reg/rec is bad. However I would not trust a dealer to test components on a 40 year old bike. Most mechanics do not know anything about these bikes anymore. The way to test the stator is is shown in detail in the Factory Service manual, which can be downloaded for free from the manuals section at the top of the home page.
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[Re-run]

Hard to say for sure, but I took my coils to a stealership, they couldn't get a reading from them, this was almost 20 years ago. I'm still using them. Tells you about the state of most dealers and their techs.

What is the brand of R/R you bought?Do you still have the mechanical regulator and rectifier?
If so, swap them back in and see what happens. Some solid state units have been known to not be the best quality.

[ilmod]

It is an ElectroSport R/R. I took it to them and they tested it and said it is good and doing what it should do, meaning it is seeing a 1.5 - 2v lower voltage at its input compared to whats actually being sent to the battery so it thinks it needs to increase voltage. That actually makes sense. I'm trying to figure out what is cause the big difference between voltage at the battery and the lower voltage on the switched accessory side which is the input to the R/R.

I did put the original mechanical R/R back in and I can adjust it down to about 15v across the battery, but that really only compensates for a real problem. The input voltage should be the same or only less than .5v off from the battery.

When I take out both the head and tail fuse (removing pretty much all accessories from the circuit) it actually doeas work with the new R/R. The input voltage is only about .5v lower and the R/R puts about 15v across the battery. I have disconnected each light and accessory one at a time and nothing on it's own makes a difference. When I put the fuses in the problem comes back.

I am beginning to think I should just replace the entire wiring harness. Has anybody done that and got improved electrical?

[LukeM]

The discrepancy between the battery side and the load side is interesting.  Makes me think there's a grounding problem somewhere.  Verify the green wire is tight and corrosion free where it connects to the frame.

Agreed that the FSM for your machine is the best resource to troubleshoot this effort.  
Luke M

[TOOLS1]

I think I understand what the problem is now. All that technical talk confuses me. Have you tried a jumper wire from the battery to the reg/rec input to see if that corrected the over charging from the low volt input? That would sure confirm the problem. As for lower voltage coming from the switch, these switches do go bad.
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[ilmod]

I did jumper from battery to reg input and I got a 14.9 - 15 volt output to battery which I believe is good. So the reg is working. I think I will order a new wiring harness from VintageCB750.com
The only other thing I can think of is that the new ignition coils are loading it down but they don't seem to be drawing too much. Any thoughts before I replace the wiring harness? Thanks

[Re-run]

Well, they shouldnt be doing that much. what ohm were the coils? Stock is 5, but I have seen 3s used. They just chew through point much faster.