Lucas A127 Alternator wiring question.

[Wandering Star]

I have a Beta 20hp engine fitted in my boat. The standard 40 amp alternator was kaput so I purchased a new 75amp alternator to replace it.

Because I don’t understand alternators & other electrickery stuff, my neighbour wired it up for me, he has since moved house (probably got fed up living next to me) and with the boat being ashore, we never got to test the new alternator. However, with the boat now afloat I started the engine but the Basic Beta control panel charging indicator light remains on. Even if I increase the revs, it remains stubbornly on. What do you think is wrong? Which terminal on the back of the alternator should the “exciter” wire be connected to? How do I check if the alternator is working? I do own a multimeter but have never learned how to properly use it.

I’m attaching the eBay link of the alternator I bought Pardon our interruption... and if you scroll through the pictures you can see the connection points on the reverse, also a picture of the back of the alternator as it’s wired now (but hanging loose) where you can see what I believe is the wire between the control panel & the alternator.

As you can guess, I don’t really have a clue what I’m supposed to be looking at here so what Ive written maybe helpful or not. All I’m concerned with is charging the blooming batteries which I don’t think can be happening if the charging light is illuminated.

 

[Alex_Blackwood]

I have a Beta 20hp engine fitted in my boat. The standard 40 amp alternator was kaput so I purchased a new 75amp alternator to replace it.

Because I don’t understand alternators & other electrickery stuff, my neighbour wired it up for me, he has since moved house (probably got fed up living next to me) and with the boat being ashore, we never got to test the new alternator. However, with the boat now afloat I started the engine but the Basic Beta control panel charging indicator light remains on. Even if I increase the revs, it remains stubbornly on. What do you think is wrong? Which terminal on the back of the alternator should the “exciter” wire be connected to? How do I check if the alternator is working? I do own a multimeter but have never learned how to properly use it.

I’m attaching the eBay link of the alternator I bought Pardon our interruption... and if you scroll through the pictures you can see the connection points on the reverse, also a picture of the back of the alternator as it’s wired now (but hanging loose) where you can see what I believe is the wire between the control panel & the alternator.

As you can guess, I don’t really have a clue what I’m supposed to be looking at here so what Ive written maybe helpful or not. All I’m concerned with is charging the blooming batteries which I don’t think can be happening if the charging light is illuminated.

View attachment 206263

This may help. However at first glance at your photo, looks asthough indicator is on correct connection. It looks as though the Negative is connected to the ac tacho output Cannot see an obvious -Ve connection from picture. Possibly bottom right centre? No doubt Paul R will be along with definitive. Not sure about your loose wire sorry.

 

[S04]

This I think should show how the original 40A alternator was wired, however, the wire colours don't seem to match!

I agree with Alex, the thick black wire looks like it should be a -ve so connecting it to the W terminal looks odd.

 

[peteK]

The original alternator was probably isolated earth return,which this doesnt have so connect the black wire to one of the casing bolts.

 

[PaulRainbow]

The big black wire is 12V negative, connect to a case bolt as PeteK suggests.

Can't see what the brown/black wire is connected to, but it should be on the spade terminal next to B+ (the big brown wire).

Brown/white looks correct.

If there is a black/blue wire it should be connected to the W terminal (where the black one is currently fitted)

Hopefully having ran the alternator with the negative wire on the W terminal won't have damaged the alternator.

 

[MikeBz]

If the original was isolated earth (0V) then your engine will now not be isolated and may be more prone to corrosion.

 

[Alex_Blackwood]

There is a female spade connector visable in the OP's photo. Is that the original Tacho ??
Edit:- BTW did your neighbour leave a forwarding address or was it a "Hit and Run"

 

[Wandering Star]

Right, thanks to everyone who offered advice. I’m working on the boat tomorrow provided it’s not piddling down and I’ve got a much better idea of the wiring scheme of things. Not quite sure what MileBz reply means? And how can I check whether Ive already damaged the alternator Paul?

 

[PaulRainbow]

Right, thanks to everyone who offered advice. I’m working on the boat tomorrow provided it’s not piddling down and I’ve got a much better idea of the wiring scheme of things. Not quite sure what MileBz reply means? And how can I check whether Ive already damaged the alternator Paul?

Wire it as per post #5, if it doesn't charge, take it to an auto electrics place that does starters and alternators for testing. You can tell if it's charging by checking the voltage at the battery with your multimeter, should be 14+ volts.