Low voltage at battery. Is it the alternator or regulator?

[discontinuuity]

I've had trouble for some time with a dim headlight, signals that only work sometimes, and a battery that tends to go flat. The other day I finally put a multimeter to the battery terminals (with the battery disconnected) and only got 2.6 volts (at idle).

Is there any way to test whether it's the alternator or the voltage regulator that's at fault? Or is there some other component that could be causing trouble? I've looked at the wiring diagram, but I'm not exactly sure where everything is on the bike and what I should be testing.

At least the engine runs fine, so the ignition coil seems to be in good shape. I just can't ride it at night or use the electric start!

[ClemSpree]

Rev the motor some with the meter on the batt, should go up significantly, actual # should be in the manual.

Go through the charging system with a DMM and compare to what the manual sez. I'd suspect bad alternator(open stator or rotor), bad regulators with a good alternator usually let too much juice through and cook batteries.

I actually need to do this myself....

[otto-man]

I had same problem with 1986 Spree (dim headlight but ran good). Replaced the regulator/rectifier.....problem solved. The headlight is powered by the alternator not the battery, so even with a dead battery your headlight should work.

[discontinuuity]

Well my regulator does look pretty beat up. But if the headlight runs directly off the alternator, why would replacing the regulator fix it? Does it go through the regulator first? I can't really tell from the wiring diagram.

[Pete M]

yes

[ClemSpree]

+1 blown regs can also blow bulbs if they fail in the opposite direction, i.e. letting too much through.

[Wheelman-111]

Greetings:

Sometimes the battery itself is the problem. Usually, in fact, if it's over 3 years old. Consider a new one, correctly charged on a charger. Or try charging yours. If you cant achieve 12.9 volts, it's toast.

[discontinuuity]

Found a trick here: http://www.hondaspree.net/phpBB3/viewto ... =3&t=23555

Now I just need to clean out the carb and get it idling so I can test it.

[mousewheels]

You don't need to build a rectifier/filter circuit. What the guy did there works, but is not necessary.

Set your meter on AC Volts. AC volts *are* what output of the stator is on the White (Regulator AC input) and Yellow (Headlight and Bystarter power) wires.

The White should be over 15 vAC when reved up
Yellow should be below 14.v or so rev'ed. The regulator works to keep the Headlight voltage from rising too high at max RPM. That would result in early lamp replacement.