REQ: Electrical help - 83 Honda Shadow 750

 Alright, Im finally frustrated enough to ask for help.  1983 Honda Shadow
750C.  The battery is not charging.  I can charge it okay with a charger,
but after an hour on the road, the battery is too weak to power the starter.
This is, needless to say, a serious inconvenience.

For you diagnosticians out there, here's what I know:
-The battery is brand new. (I first thought that was the problem.)
-The rectifier/regulator was replaced with a junkyard part that was bench
tested to be okay on the rectifier side.  No change in the symptoms.
-The alternator leads (3 yellow wires) were checked for continuity with an
ohmmeter.  All seem okay with about 6 - 8 ohms each.
-With the bike running, the alternator leads were checked for AC voltage
going in to the rectifier,  All 3 yellow wires showed about 14.5 V to
ground.  That's probably a bit weak, but is it enough to prevent charging?

Any tips/help on getting me back on the road?
(FWIW, no shops in my area will touch a bike this old.  I'm on my own here.)

TIA,
Joe

 rb608 wrote:

http://www.electrosport.com/electrosport_fault_finding.html

Most electrical problems result from bad electrical connections. They can be
loose, corroded, or burned.

The first thing I would check is the battery cable connections, including
where the battery ground cable attaches to the frame and the grounding jumper
that attaches the engine to the frame. I have even heard of old engines with
crankcases that were so badly corroded the starter couldn't find a good
return path to ground.

Check the voltage regulator case for a good ground to the frame, if it
requires using the motorcycle chassis instead of a dedicated ground wire. If
the regulator bolts to a metal plate that holds a lot of electrical relays
and fuse panels and flashers, etc., make sure that the metal plate is
grounded.

Check the connectors that come from the alternator stator. The plastic
connector shouldn't be melted, and the pins shouldn't be corroded or burned.
A
lot of riders get so disgusted with the bad connections, they cut the
connector off, strip the wires, twist them together, and solder them
permanently together.

Cutting the connectors off and soldering the wires together makes a lower
resistance connection, but, if you ever need to replace the parts, you can't
just plug new parts in, you'll just have to get the soldering iron out again..

 wrote:

Sounds like good advice, thanks.  I've been tackling it from a "macro"
strategy of replacing obvious major parts, but methinks I will need to
start tracing continuities other than the obvious.

Joe

 
Please bear in mind that it's much easier to measure voltage
differences between points that should be at the same potential
than it is to measure "continuity". Milivolts are easy on a
somewhat modern DVM. Milliohms are unmeasurable practically.

In your situation, milliohms might be important. It's best
to rely on millivolts.

I'd look for less than 100 mV from RR to battery, on
both plus and minus sides. Anything bigger, work on
the connectors. Get rid of them if you must.

bob prohaska