What is R and L on my alternator?

[Bidrago]

Engine: Cummins Mercruiser 1.7 DTI with alpha one gen 2 sterndrive.
The alternator have L and R terminals. L is for the charging light on dashboard. But what is R doing?
Does R output the same power as B+ ? Wire scheme is attached.

Found this on internet
WHAT IS THE “R” TERMINAL OF THE ALTERNATOR FOR? The “R” terminal or Relay terminal as it is sometimes called, provided some of the alternator’s output and was used to power electric tachometers, a dash light, hour meters, or other modern accessories. In some applications it was connected to the dash light to give notice if the alternator was failing to charge

A key to help identify alternator terminals
R = Relay - Output to charge relays, etc

I guess the alternator isnt 100% functional?

 

[VicS]

"L" is the warning light connection as you realise

"R" has at feed to it from the ignition switch. It is connected inside the regulator to " L" by a resistor ( 50 ohms ) It provides the initial excitation for the alternator traditionally provided by the current flowing through the warning light. It allows an LED, which would not provide enough current, to be used as the warning light,
If it is disconnected the alternator will probably not start to generate unless the warning light is a sufficiently high enough wattage filament bulb to provide the excitation current

It is not an output!

I guess the alternator may be a Hitachi one ?
This diagram I hope explains ( P is an output for a tachometer ... not applicable in your case))

 

[Bidrago]

Thank you very much for your reply! I do not know what alternator it is. It is one like this Mercruiser Alternator on eBay

I have to give the engine some rpm before it starts charging. That cant be right? So maybe there is a broken wire somewhere between ignition and R on alternator? Attached is wiring for my instrument panel.

 

[PaulRainbow]

Thank you very much for your reply! I do not know what alternator it is. It is one like this Mercruiser Alternator on eBay

I have to give the engine some rpm before it starts charging. That cant be right? So maybe there is a broken wire somewhere between ignition and R on alternator? Attached is wiring for my instrument panel.

The Ebay listing looks like an aftermarket copy of a Mitsubishi alternator.

L is the warning lamp.
R is the voltage sensing terminal.

It's not unusual to have to increase engine RPM for the light to go out, what sort of engine speed are we talking about ?

 

[Bidrago]

The warning lamp doesnt light. But I can see on the voltage gauge that it doesnt start charge before I rev it up a little. I put it on neutral and rev it up a little bit. I dont know the rpm because the tach is not working yet.

 

[VicS]

The warning lamp doesnt light. But I can see on the voltage gauge that it doesnt start charge before I rev it up a little. I put it on neutral and rev it up a little bit. I dont know the rpm because the tach is not working yet.

The warning light should light when you first switch on and go out as the alternator output reaches the voltage at which the battery should start to charge.

Its not un-common for an alternator to not start charging until revved a bit but the warning light should stay lit more or less until it does.

Id check the warning light and its circuit.

I' d check the volts on the L and R terminals . You should get a reading equal to battery volts on "R" as soon as you switch on and a lower reading on the "L". When the alternator starts to charge the volts on "L" should have risen to about the same as battery volts.

If the glow-plug control relay is working correctly any reason for battery volts not appearing on "R" will be local because the white green wire from the ignition switch is also the +ve supply to the relay control circuit
I note it also supplies the tach sensor. If tach does not work it may be for the same reason OTOH that may be a completely different issue.

There are numerous possible reasons for what you observe . Systematic testing is the way forward

 

[PaulRainbow]

The warning lamp doesnt light. But I can see on the voltage gauge that it doesnt start charge before I rev it up a little. I put it on neutral and rev it up a little bit. I dont know the rpm because the tach is not working yet.

Doesn't light at all, ever ?

It's helpful to provide all of the details of the issue in post #1, rather than drip feeding it throughout a thread.

 

[Bidrago]

I used my multimeter today and found out the tachometer doesnt have any grounding. So strange. I cant find out where the break is,. Anyway... I connected a new ground and now the tachometer works.

The battery lamp lights up when I turn the ignition on and still light up when engine is started. When I rev it up a little it is gone. And found this on L and R on the alternator. I have sprayed it with oxide clean and will mount it tomorrow to see if it works