Topic: 2001 Nighthawk 750 charging system issues

[noonesshowmonkey]

The bike: I bought it for a song from a donation-driven seller, who got the bike for free when it was donated.  Unknown how long it sat.  The bike was sitting on a battery tender, started sluggishly, idled rough, but it ran.

The issue: the battery refuses to charge, indicating a charging system failure.

What I've done so far:

1) I bought a new battery, assuming that the battery on the bike was dead.  It may well have been fine, as swapping to a fresh battery didn't change the fact that the charging system was not charging.

2) I pulled the fuse box open and checked the resistance and voltages on the fuses.  Nothing out of the ordinary.  I went along the wiring harnesses and wiggled everything, took apart the headlamp and wiggled everything.

3) bought an OEM stator and replaced the old one.  The old one was looking rough.  Touched off the bike and it started immediately, and I thought I had this one in the books.

What the bike is currently doing:  the ignition switch and the starter switch are flakey.  Sometimes, I have to alternate between key ON/OFF on the ignition switch, and RUN/OFF on the starter switch in order to get the headlights to light.  This LOOKS like where my problem is: one (or both) of the switches.  Likely, there is also a ground fault there that is causing my parasitic battery drain, too?  Maybe?

I am pretty stumped as to how to move forward.  I can buy a fresh starter switch without too much headache, but an ignition switch will require re-keying the whole bike...

Any ideas on how to further diagnose this?

[Mr. Mike]

It’s not clear if there is a charging issue just yet, or some problem with the handle bar switch or key switch pulling the battery down, or something else.

Have you run the bike and monitored the voltage at the battery terminals at varying rpm’s?
Say 2K-3K and maybe around 4K should show a voltage starting at around 12.5, then 13 and on up to 14 something. These are close values, but the point is it should increase on up to the 14 volt scale as the rpm’s increase.

There may be an issue with the regulator or rectifier. There is ample information on how to test these components available on a google search.
Do some more testing before spending more money.

[noonesshowmonkey]

I rechecked the standing system drain per the manual, and my ohm meter read 0.  The needle didn't even jump.

So, I pulled apart the regulator/rectifier, and found that pins 2 & 3 on the female connector were blue-green, and obviously oxidized from excessive heat.  Putting a multi-meter on the R/R, I found that pins 2 and 3, when connected to the ground (pin 7) were providing significantly less resistance than the specified ranges.

Between the female pins being oxidized and the out of spec readings, I thought that I'd discovered the source of the problem.

I pulled the R/R unit, ordered a new one, measured the battery voltage at 12.6v, and then put the bike away for the night.  In the two days it took for the new R/R to arrive (oh, sweet modernity!), the voltage on the battery didn't drop one bit.  12.6 on the meter when it came time to put the new R/R on.

After that, the bike started easily, but idled rough.  Some fresh spark plugs later (all four were carbon fouled, and one of the exhaust pipes was cool from a non-firing cylinder), and the bike has come back to life.

The learning here is to just trust the manual, and run through the specified tests before wasting money on parts.  Woops!

[noonesshowmonkey]

So, replacing the R/R was definitely a good idea, but it didn't actually solve the problem.  The bike still had a slow drain (especially when running), and more importantly wasn't charging the battery.  I picked up an OEM stator for a song on e-bay and it came in the original Honda packaging.  I was stunned.

After putting that on the bike, the battery held charge all winter, took a fresh charge in the spring, and started immediately upon reinstallation of the carbs after I'd rebuilt them.

In short, I chased every wiring harness, checked very fuse, replaced the Regulator/Rectifier, and eventually the Stator.  Essentially every electrical component on this bike was touched during the diagnosis & repair.  The good news: there's not a lot to mess with on this design, and the total in parts to fix everything was maybe $300ish, including a new battery, regulator/rectifier, and stator.  While it isn't cheap, knowing that everything is working is priceless when it comes to diagnosing any future problems.