Alternator question

Correct, the smaller goes to warning light > 12v +ve, both the other large ones are alt output.
For the warning lamp you need a filament bulb not an LED one
 
Normally the second large terminal is paralleled to the other large terminal to give two full capacity output's for industrial purposes, and often one terminal would charge the battery and the other would run things such as lights.

However; depending upon the type and model it could also be for the battery sensing terminal if the alternator is battery sensed instead of machine sensed.
 
Assassin said:
Normally the second large terminal is paralleled to the other large terminal to give two full capacity output's for industrial purposes, and often one terminal would charge the battery and the other would run things such as lights.

However; depending upon the type and model it could also be for the battery sensing terminal if the alternator is battery sensed instead of machine sensed.
Click to expand...

Just to add that if the plug and alternator have been married and working satisfactorily suffice to say the above holds good. However, be also aware that if the Lister was always a marine variant then it may well have been fitted originally with a full blown marine alternator and not a automotive type as appears. In which case the plug blank was used for the -ve return, and battery sensing terminal are small terminal rather than the large and are not in this three terminal cluster but remote in this cover. The reason behind my thoughts are that if at a latter date you come by a Lucas Marine fully insulated alternator the necessary wiring may still be in situte and with the usual mandatory checks could still be used. You may be able to see the alternator type riveted to the stator external case which would help with advice.

If it helps the boat may have two batteries one for engine starter and the other for general service. As quoted the spare larger terminal can be used in parallel with the existing of the same size and length to supply a split charge diode or a voltage sense relay to charge both batteries simultaneously (which may be the case). Can be reassuring if you are tempted to use power when at anchor, and only have the engine start battery! The benefit of the additional wire would helps to reduce volt drop in the charging circuit, the alternator output being self limiting.
 
Unfortunately I don't have any history of the wiring, it's been left semi abandoned for 8 years and the whole console was rotted and wiring was a chopped up mess. I'm in the process of fitting new decks, bearers and gunwales. I doubt I'll ever need 2 banks as it's an open 26' fishing boat that'll be used for potting and hand lining. Bonus is the sr3 has handraulic back up starter.
Just want to make sure I make the new loom correct. Will be putting an ammeter and voltmeter and don't want to damage the alternator
 
I would suggest the first port of call is establishing exactly which alternator you have and get the correct wiring diagram for it.

Surfacesub has highlighted different variants and different configurations, and while this may appear to muddy the waters slightly he has actually and correctly highlighted another variant and potential variations of wiring.
 
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