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 Alternator wiring

 Created by: Frogeyeandmini
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 Posted: Dec 11, 2019 01:50PM
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Thanks Doug, its always nice to know “why”.......

Cheers, Ian

 Posted: Dec 11, 2019 07:45AM
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GB
+ve vs -ve earth cars is complicated and dependant on which part of the car you wish to dissolve !
Wiring loom or chassis is the basic choice, and it generally switched at some point in the 60s as 12V systems became the accepted standard over 6V.

 Posted: Dec 11, 2019 06:03AM
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US
I have never understood whether positive or negative earth offers any benefit.  However, it is worth mentioning that it was not just the British who used positive earth.  Up until the late 1950s you could find some American cars with positive earth.  There were also some cars that still had 6V systems.

For some historical takes on polarity see the link below to Barney Gaylord's MGA Guru website.

Link to MGA Guru Polarity Article

Doug L.
 Posted: Dec 10, 2019 05:52PM
 Edited:  Dec 10, 2019 05:57PM
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Not that I would trust me with electrical stuff.... but this works..

My aftermarket big output alternator has two spades (one big, one small) both marked "+", one small spade marked "IND" and two large insulated (from the alt body) threaded posts.  I can't see any marking on the posts.

I run a large (brown) wire from the big spade to the live terminal on the solenoid - which then connects to the battery +.  A small black wire runs from the "IND" spade to (presumably) the charge light in the speedo (via the voltage reg??? - maybe - its been so long since I've been in there I can't remember).

I have not (and would not) run a charging wire (alternator+) to the coil.  My coil is fed from the solenoid terminal and hence the battery.  I would think that, if you charge the coil from the alternator and the fan belt quits, the engine will immediately go out in sympathy.... which might be inconvenient.

I would have thought that your new alternator would have come with some form of instructions that identified the various terminals.... 

My setup has run successfully for over 20 years ..but that's the only claim to authority that my suggestions warrant 

Cheers, Ian

PS Does anyone know why most (all the ones I've seen) modern cars (..and alternators) run negative Earths    And why most (older?) Brit cars run +earth?????  Physics 101 was so long ago I can't remember which way the electrons flow ..but that shouldn't affect the efficiency of the circuit.. should it???

 Posted: Dec 10, 2019 02:35AM
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US
It sounds like you have a Denso alternator.  It would help if you identify which alternator you have and perhaps post a picture of its butt end with the terminals shown.

Doug L.
 Posted: Dec 9, 2019 06:47PM
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So I have a new small high amp alternator. It has a big post and two spade connectors. One of the spade post you run a jumper wire from a key on wire to the + side of the coil. That makes sense. The second spade you connect to the brown wire with the yellow stripe. So now you know if your mini is charging. The red light comes on and then off when the RPM's are high enough, beyond slow idle. This makes sense. Now I'm hesitant about the big post. You connect the BIG brown wire to it. that makes sense. Now, this is where I'm hesitant. Do you also connect a constant wire from the positive side of the battery to the large post or is that what the big brown wire is doing?

I appreciate anyone's help.