How to I connect up this alternator?

Rivers & creeks

Rivers & creeks

Well-Known Member
Joined
23 Nov 2004
Messages
10,924
Location
Norfolk
Visit site
The engine room rewire lead to me stupidly, daftly, irritatingly and annoyingly disconnecting the wires from the alternator. I then ran it for 20 or 30 seconds before realising - doh. I want to reconnect it all and see if I've been lucky and haven't killed the diodes. Can you tell what wires should be on the back of this alternator? It's one of the ones that needs to run through a light on the control panel to work, the light didn't go out when I turned over the engine with the wire(s) disconnected.

Thanks - Simon

View attachment 28462View attachment 28463View attachment 28464View attachment 28465
 
It's a Lucas-type alternator. The warning lamp connects to the small blade (IND) at the bottom of the 3 blade area (looking at your pic). The battery negative connects to the case, on yours it looks like the connection has been made to the bolt next to the mounting bracket. The battery positive connects to the + terminal at the bottom of your pic. The tachometer connects to the W terminal at the right of your pic. Here's a pic showing the moulded markings on the case.

lucas_zps236c162b.jpg
 
Lazy Kipper said:
The engine room rewire lead to me stupidly, daftly, irritatingly and annoyingly disconnecting the wires from the alternator. I then ran it for 20 or 30 seconds before realising - doh. I want to reconnect it all and see if I've been lucky and haven't killed the diodes. Can you tell what wires should be on the back of this alternator? It's one of the ones that needs to run through a light on the control panel to work, the light didn't go out when I turned over the engine with the wire(s) disconnected.

Thanks - Simon
Click to expand...

You should not have done any damage to the alternator by running it while disconnected. What can/does blow the diodes is the voltage surge that occurs if you disconnect it from the battery while it is actually running.


Puzzled though by the fact the the warning light did not go out. Once it is disconnected from the alternator I'd have expected to not illuminate at all.
 
Last edited:
Thanks to both of you for the replies. I think the brown and yellow wire in my picture goes to the control panel for the red warning light. Any idea why there are two positive spades and does it matter which I use to go to the split charge diode box?

Thanks.
 
Lazy Kipper said:
Thanks to both of you for the replies. I think the brown and yellow wire in my picture goes to the control panel for the red warning light. Any idea why there are two positive spades and does it matter which I use to go to the split charge diode box?

Thanks.
Click to expand...

I'd think probably both + spades are connected together. Check with a meter on lowest ohms range (or better with the continuity buzzer if the meter has one)

A heavy wire will go on one and to the diode splitter. warning light wire will be relatively light. Maybe different size spades anyway. Actually designed i think for a plug carrying all the connections

You have not said what engine... is there a wiring diagram in the manual or one to be found on line ?
 
Lazy Kipper said:
Thanks to both of you for the replies. I think the brown and yellow wire in my picture goes to the control panel for the red warning light. Any idea why there are two positive spades and does it matter which I use to go to the split charge diode box?
Click to expand...

You connect the + terminal to the diodes. You don't use the 2 larger spade terminals.
 
So the + cable hasn't been disconnected? Maybe I just disconnected it from the diode splitter - but looking at my photos the W connection isn't there and the rev counter definately works.
 
Lazy Kipper said:
So the + cable hasn't been disconnected? Maybe I just disconnected it from the diode splitter - but looking at my photos the W connection isn't there and the rev counter definately works.
Click to expand...

Your rev counter may use a sensor on the engine. If you're saying that the wires in your photo are as it was previously wired, I'm intrigued as to why the positive wire is black and the negative wire is red.
 
pvb said:
Your rev counter may use a sensor on the engine. If you're saying that the wires in your photo are as it was previously wired, I'm intrigued as to why the positive wire is black and the negative wire is red.
Click to expand...

Perhaps you've met the previous owner? He sometimes had the courtesy to tape a bit of red electrical tape to a black wire to indicate it was positive, often not. Actually in this case the red you can see is a wire going past the alternator, now tidied up.
 
pvb said:
You connect the + terminal to the diodes. You don't use the 2 larger spade terminals.
Click to expand...
I hate to disagree outright, but the two + terminals at the main charge out path that should be connected to the battery. The 'ign' goes to the ignition switch via the charging lamp and the 'w' is the tacho connection.

You need the charging lamp via ignition switch to excite the alternator.

On a car the + terminals are permanently live. You don't need to use both - one will do and its only one that's used in some installations.

Thirty years ago between University and College I used to build those alternators. :)
 
Lazy Kipper said:
Now I'm confused.
Click to expand...

Why would you use a push-on spade connector for the high current alternator output when you can use a secure stud terminal?

If you need more reassurance, look at the excellent Tony Brooks website ( http://www.tb-training.co.uk/16elect.htm ), scroll down to nearly the bottom of the page and look at the diagram showing connections to a Lucas A127 alternator, which is similar to yours.
 
Problem with the spades is they cannot carry a lot of amps hence the reason theres two of them. i think the std blue size max is 18 amps not sure on the yellows?
Spades are the same as crimp terminals pretty weak, heat shrink ones are pretty good though.


Lynall
 
Last edited:
lynall said:
Problem with the spades is they cannot carry a lot of amps hence the reason theres two of them. i think the std blue size max is 18 amps not sure on the yellows?
Spades are the same as crimp terminals pretty weak, heat shrink ones are pretty good though.


Lynall
Click to expand...
I don't know why Lucas used push on terminals for the main current carrying job but they certainly did. There was a preformed block that plugged into the 'hole' and it often only used one of the two large push on connectors (although they are available to be used in parallel if needed). Perhaps it was cost? Push on spades are cheaper perhaps?

As far as I am aware the electrical characteristics of crimp push on vs heat shrink are exactly the same but I am not sure what you mean by 'weak'. Heat shrink certainly improves the durability of the connection as it reduces the mechanical stress of any vibration or bending of the wire.

I've just looked at the original posters photo's again and see that its actually not the ACR type I was referring to in my previous post. If there is a insulated post with + next to it then that is the main charge 'out' connection and ignore my previous.

I had only glanced at the 'cleaned up photo' in the first reply and managed to say something stupid as a result.
 
Last edited:
john_morris_uk said:
I've just looked at the original posters photo's again and see that its actually not the ACR type I was referring to in my previous post. If there is a insulated post with + next to it then that is the main charge 'out' connection and ignore my previous.

I had only glanced at the 'cleaned up photo' in the first reply and managed to say something stupid as a result.
Click to expand...

Thanks for re posting John, that seems to clear things up.

I'm very grateful to everyone for taking time to help sort this out.

Simon
 
Hello, thanks for this thread has begun to clear up alternator wiring for me. I am stuck because my replicas Lucas A127 which is identical to the picture posted here except it lacks a B- stud? If you are still on this group any suggestions welcome. Thanks
 
You must log in or register to reply here.

Share this page

Top