Alternator Woes

[Vasco]

Yamaha 3GM30F with a small (40amp?) Hitachi alternator. The alternator is new and internally regulated. The alternator works but goes way up to 15v. right away on nearly fully charged batteries. I assumed the regulator is not working.

I understand ( or maybe misunderstand) the regulator is regulated by a sense wire which senses battery voltage. The alternator has a 2 prong plug with "L" and "R". I think the "L" is lamp and "R" is regulator.

I am electrically challenged but tested the "R" on the plug when the ignition switch was switched on. NO voltage. I assume (maybe wrongly) that the regulator is not working due to no voltage on the sense wire.

The wiring harness that the sense wire is in is really old so there might be a break in the line. (Don't know how to test this).

If the above is correct can I just add a wire from the "on" side of the ignition switch and run it to the "R" part of the 2 prong plug? I really hate to fool around with the old harness.

All help appreciated.

[model 10]

That is a little confusing. I thought an internaly regulated alternator did not have a field wire. I have a one wire Delco as a spare and it just has the one wire, the power lead. It's a terrible unit, you need an external regulator with an alternator.

[Vasco]

Anyone with knowledge on this subject?

[Wotname]

Originally Posted by Vasco

Yamaha 3GM30F with a small (40amp?) Hitachi alternator. The alternator is new and internally regulated. The alternator works but goes way up to 15v. right away on nearly fully charged batteries. I assumed the regulator is not working.

I understand ( or maybe misunderstand) the regulator is regulated by a sense wire which senses battery voltage. The alternator has a 2 prong plug with "L" and "R". I think the "L" is lamp and "R" is regulator.

I am electrically challenged but tested the "R" on the plug when the ignition switch was switched on. NO voltage. I assume (maybe wrongly) that the regulator is not working due to no voltage on the sense wire.

The wiring harness that the sense wire is in is really old so there might be a break in the line. (Don't know how to test this).

If the above is correct can I just add a wire from the "on" side of the ignition switch and run it to the "R" part of the 2 prong plug? I really hate to fool around with the old harness.

All help appreciated.

There should be battery voltage on the R wire when the engine switch is ON.
It is the same battery feed that causes your warning lights to illuminate so if your oil and charge warning lights have illuminated when the engine switch is ON and there is NO voltage at R, then yes, the loom has failed - probably at the engine harness connector.

Running a new wire from the ON side of the engine switch to R will work.

[Wotname]

FWIW, the L wire goes to the charge light.

[Vasco]

Thanks, Wotname. Yes the lights on the panel come on when the ignition switch is on. I think I'm going to run a new wire to the alternator plug from the on side of the switch.

[Wotname]

Originally Posted by Vasco

Thanks, Wotname. Yes the lights on the panel come on when the ignition switch is on. I think I'm going to run a new wire to the alternator plug from the on side of the switch.

That will work

FWIW, on my panel (about 2002), the ON side of the switch is marked as AC but this can vary depending on the date of manufacture of the panel.