The battery warning lamp on the dash of my S does not illuminate when I turn the igniton key on. It has a Lucas 15AC alternator with 4TR external regulator.

I swapped in another spare externally regulated 15AC but still no light. Also swapped in a spare 4TR box but still nothing. If I ground the brown/yellow wire going to the IND terminal the dash light comes on.

I have a spare 70 amp Lucas Rover altrenator (GXE2297) with internal regulator, I put the wire in this and grounded the alternator body and the light came on.

Does this mean both 15ACs are defunct, maybe caused by bad rectifiers? The 70 amp Rover alternator has 2 battery out charge tabs and a metal charge bolt post. Which one should I connect the thick brown wire that goes to the solenoid to? Presumably it will need a thicker wire to cope with the higher output, what gauge do you recommend?

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Slide
1965 Mini Van (1360)
1970 Mk2 Cooper S (1310)
1978 Rover SD1 V8 (4.6)
1996 Land Rover Discovery V8 (4.0)

Check the alternator brushes. One wears faster than the other.

Connect the output to either big terminal, I added a 2nd wire due to the extra output.

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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.

The first thing to ascertain is that you in fact have a 15ac with the large black cover rather than the later 15ac (which has an internal reg) which does not have the black cover.
Here is a diagram you can follow to make sure your wiring is correct



As the Doc says the brushes may have worn or the small spade connectors may be loose or corroded.

As for the 70A you may never draw more than 35 to 40A so the standard wir will be fine however I run 2 x 6 to 10mm wirss, one to each large lucar spade to the solenoid thus a twin wire in parallel.

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Cheers Dave.

Thanks guys, yes 15AC on my S has black plastic end cover.
The 15AC on my van does not and has internal regulator.

I know 70 amps is overkill, although it does have heated
rear screen, but this alternator is a new unit and all I have in stock. Not too worried about retaining
originality.

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Slide
1965 Mini Van (1360)
1970 Mk2 Cooper S (1310)
1978 Rover SD1 V8 (4.6)
1996 Land Rover Discovery V8 (4.0)

Two 6mm wires in parallel will handle 35 A each so 70A total, all good. Bigger Alt also does it easier.
It is worth noting that the ind lamp has permanent 12v on 1 side and the other changes.from earthed through field winding for lit to 12v through field for off so 12v on both sides is off/charging.

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Cheers Dave.

Unrelated maybe..
I just put my motor back in, has a later alternator with internal regulator.
It's charging 14.3V but the light isn't working.
I haven't disturbed any wiring, question is how can it charge if the bulb is blown?
I'll ground the wire in the morning and see if it lights up.

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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.

Many years ago I accidentally plugged my IND wire onto a 12v terminal and it had a similar result - I assume that yours are all on the right terminals?

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Both 12V terminals have big lugs and wires to the solenoid.
The only other terminal there is the 1/4" 'ind' one.

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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.

Well there's 12.4V on the ind wire with ignition on.
If I ground it the light doesn't work. If I run without the wire it doesn't charge.
Put wire on it's charging 14.3V.
Hmm...
Maybe the bulb holder has slipped out of the speedo. It's a 2 wire connector so alternator still works if out.
I need to pull the Dellorto and manifold off to see the speedo but as I've just got the car mobile again it can wait.

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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.

Update
It's charging fine. I don't really care that the lamp isn't working, I have ordered a Voltmeter and 2x USB adaptor for the cigarette lighter socket it has.
More useful.

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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.

If the car originally had a dynamo then whoever rewired for alt may have got it wrong, is the control box still in situ and wired?
If car had a 10, 11, or 15ac ext reg originally then it may have had a 3aw warning light relay (not common but not unknown either) which will keep the alt charging even if the ind lamp blows, the coil of the 3aw gives thefield its load.
If it has an 8tr still wired in then the this could also allow charging with a blown ind lamp.
Or, as you say the lampholder may have fallen out.

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Cheers Dave.

It is a 1970 , used to have a 15AC alternator. I just pulled the plug off the regulator years ago and put the brown yellow wire on the 16ACR or whatever it is. The light worked fine for 20 years, it must have fallen out of the speedo.

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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.

As you know, one side of this light is connected to the ignition switch and the other side to the IND terminal of the alternator. If it charges OK with the IND cable connected to the alternator, but does not charge when IND is not connected, then yes, the bulb holder has fallen out. The alternator does not charge when the IND is not connected because the field windings need to be energised by the current coming from the ignition switch, through the indicator light, through the field windings, to earth. This gets the whole thing started once the engine starts to turn. When the alternator revs rise, output from the stator windings take over (via the regulator) energising the field coils.

My point was, and still is, that the ind wire from the alternator goes via the external regulator which although no longer needed, if still connected could be supplying battery voltage to the field coil. If you pull the brown / yellow connector off the ext reg and the alt stops charging then the ind lamp is blown or disconnected. If it still charges then tbe lamp is good.

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Cheers Dave.

I pulled the external regulator off years ago. The multi pin regulator plug is still there.
Voltmeter/USB plug now installed. It read 14.2V during a run this week.

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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.