Lucas LRA00374 wiring

Riley RMF · Post by **Riley RMF** » Tue Dec 19, 2017 8:10 pm

Trying to work out the wiring for my Lucas LRA00374 alternator, the rear view of which looks like this:

Happy enough with the 3 pin connector, which has the two larger spade terminals connected together internally. I assume I can connect my positive output from the alternator to either of these?

Also though, I can't work out what the connection with the nut on it directly under the 3-pin connector is for. There is no legend on the casing and I can't find anything on either this site or anywhere else on the Internet.

Anybody know what that's for?

Thanks

Phill

mike-b · Post by **mike-b** » Wed Dec 20, 2017 7:54 pm

Phill, Accordibg to the haynes car electrics manual that stud is a Pos that you don`t have or need to use. It has an insulator so it must be a positive.

The other connections are thus: the smaller of the three is from your ignition via the ignition light.
The other two are the positive, however though they are joined together inside both are used. The norm here is two cables are used instead of one very thick one. These two thinner cables are 4mm thick ( well mine was once ) not counting the insulation then both are connected together later. They are joined either in a connection box or soldered to a thicker cable that connect to your battery Pos sooner or later.
Lucas used this system so a very thick cable would not be needed. You could use one cable but you would need a thicker cable, the problem then is would one connection at the alternator be able to stand the current that may be drawn through it?
At the end of the day you don`t want cables getting even near hot.
Hope that helps.
Mike

Riley RMF · Post by **Riley RMF** » Wed Dec 20, 2017 10:17 pm

Hi Mike - that's great, thanks.

Just to satisfy my curiosity, any idea what the Pos stud would typically be used for?

Phill

DaveEFI · Post by **DaveEFI** » Thu Dec 21, 2017 9:39 am

Might be some form of tach output? The two terminals in parallel is because one can't handle the power output of the unit.

harvey · Post by **harvey** » Thu Dec 21, 2017 2:20 pm

DaveEFI wrote:Might be some form of tach output?

Or for battery sensing maybe.

Riley RMF · Post by **Riley RMF** » Thu Dec 21, 2017 6:02 pm

Ok - thanks guys, and thanks for the help. Think I'll ignore the lower connection for the time being, and maybe do some experiments when I'm up and running.

Have a great Christmas break

Phill

mike-b · Post by **mike-b** » Thu Dec 21, 2017 10:44 pm

I agree with all the above regarding that one alone Pos connection.

However just to throw another answer into the bag .......... Suppression for the voltage regulator.
It would stop that high wine you might get while tuned to the BBC classic music channel.