I am having a problem with my lucas 3 terminal alternator. We have had to remove the engine and we are not 100% sure we now have the wiring correct. There are 3 terminals on the alternator, my question revolves around the 2 larger ones. Can someone tell me are they both positives and where should they go. Do they both need to be connected? Clearly one goes to the battery via the solenoid,(not sure which of the 2 larger terminals this should be on) however the other appears disconnected. Is that perhaps a result of a previous modification? Also when we first put the Alternator on a test while revving the engine indicated an increased voltage 13 plus volts. However having to remove radiator, the alternator came of again and I cannot seem to get it to charge. While revving the engine the voltage stays stable at 12.4 . How finicky are the altenators? Any help really appreciated.

The 2 large terminals both go to battery `+' terminal on the starter solenoid via 2 thick brown wires.
It is not essential to use both, I've only used 1 wire for years (car originally had the 15AC alternator, which used 1 wire). It charges fine.

The small terminal connects to the brown/yellow wire which goes to the ign lamp in the speedo. Without this connected (or if the bulb is blown) the alternator will not charge.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

This is correct unless this guy has an external regulated type alternator which sometimes one of the large spades is a negative !

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There was one model (16ACR?) that used a 'sense' wire which was connected to the +ve on the Solenoid. This wire was Brown with a Blue Trace and a smaller Gauge than the Main Charge Wire (Brown). From memory this one connected to the Terminal furthest from the IND Terminal, that's the smaller one that the Brown / Yellow wire connects to.

The purpose of it is to sense the System Voltage rather than the Alt output voltage, it takes in to account the Voltage Drop on the Charge (Brown) Wire. If this is not connected, it's output is reduced.

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Convertible Mini wrote "This is correct unless this guy has an external regulated type alternator which sometimes one of the large spades is a negative !"

Yes Tony, you are right but that one (original 15AC) has 2 small terminals, for ind and field, not just 1 that he mentioned.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks for all the help especially Dr Mini. he was 100% correct about the alt light. I found a small break in the printed circuit leading to the no charge globe, after a bit of soldering it worked straight away and alternator was charging. So this circuit definately supplies the field windings to excite the alternator. Well done to all.

Printed circuit failure... very common problem. I find that a big percentage of Mini instrument clusters I remove have got a damaged or repaired Flex Printed Circuit. Easy enough to replace today and the ones available are a better quality that the original ones.

_________________
DID I MENTION THAT I AM THE BEST SUPPLIER FOR MINI ELECTRICAL PARTS AND REPAIRS?
"Let us remove your "SHORTS"