Alternator Swap: 11AC to A127

finfont

Member
Morning All:
I am attempting to swap out the 11 AC (external regulator) alternator for a more modern one with an internal regulator. A plan and schematic have been posted prior by one of the forum members. Below is the schematic:
1624884067711.png
Here's my question. Where is the "6RA" alternator relay located? I've located the Starter Relay ( it has 6RA stamped on the outside of the module, and a sticker labeled "Starter" on the underside of the module), but have been unable to locate the 6RA alternator relay. The wire that I am tracing (NP- brown with purple stripe) leads directly from the alternator into the wire loom. I've followed the loom to the starter relay, and, cannot find any module between the alternator and the Starter relay. Is it possible that my car (1972 3500 automatic p6, left hand steering) has a 6RA starter relay, but not a 6RA alternator relay? Any help would be appreciated.
 
Not all 11AC equiped cars have a 6RA relay in the charging circuit.
That was my concern. The Rover repair manual electrical diagram for this car (454, suffix A) did show the alternator relay, but, I'm pretty sure that you are correct. It is not there. I'm pretty much done, then. I don't feel confident attempting this procedure without a proper set of instructions. The reason for the attempted alternator swap is that the car "stumbles" at idle under high electrical draw ( high beam head lights, wipers, fan , etc.). I've had this 11AC alternator rebuilt, but, evidently the job was not sufficient to return it to it's initial amperage output.
As always, thank you for your help, Harvey.
 
If I were doing the conversion I would make my own small loom from the 2 larger terminals on the alternator, to the main lead into the starter solenoid from the battery, and then unplug the 4TR altogether. Then take the wires off the 3AW unit, find which wire is the earth and discard that, then join the other 2 together, then find the alternator end of that wire and put that on the third, smaller terminal in the multiplug.

If you look at your wiring diagram you have posted you should be able to see how to do what I have suggested.
 
Harvey:
That sounds doable. A couple of clarifications, please. Firstly- the 3 AW unit is a cylindrical metal module in the glovebox, adjacent to the 4TR, is it not? And, when you say "smaller terminal in the multiplug", you are speaking of the multiplug on the alternator, correct?
Thank you.
 
The wiring diagram is actually wrong for my car. It doesn't have the 6RA relay - this was removed on late 11AC models. What I did in the end was run a new pair of 10AWG wires to the battery terminal post on the floor.

I made a new loom with the two heavy wires and a pigtail for the ignition light/feedback so none of the original wires were cut at all so completely reversible. I also added in the oil pressure wire as my car had a strip speedo (no oil pressure gauge) and was converted to the later instruments. The cable then is neatly routed inside the car instead of a single cable not in a loom across the engine bay.
 
The wiring diagram is actually wrong for my car. It doesn't have the 6RA relay - this was removed on late 11AC models. What I did in the end was run a new pair of 10AWG wires to the battery terminal post on the floor.

I made a new loom with the two heavy wires and a pigtail for the ignition light/feedback so none of the original wires were cut at all so completely reversible. I also added in the oil pressure wire as my car had a strip speedo (no oil pressure gauge) and was converted to the later instruments. The cable then is neatly routed inside the car instead of a single cable not in a loom across the engine bay.
Peter:
This is pretty much what Harvey is suggesting in his reply above, is it not?
Thanks,
Drew
 
Bypassing the 3AW.... In my car this was on the left hand (drivers side in LHD). The 4TR was on the right hand (passengers side LHD).

1624889961370.png
 
Harvey:
That sounds doable. A couple of clarifications, please. Firstly- the 3 AW unit is a cylindrical metal module in the glovebox, adjacent to the 4TR, is it not? And, when you say "smaller terminal in the multiplug", you are speaking of the multiplug on the alternator, correct?
Thank you.

Correct on both counts. (Although on a RHD car the 3AW would be on the driver's side the opposite side to the 4TR.)
 
Peter:
This is pretty much what Harvey is suggesting in his reply above, is it not?
Thanks,
Drew

Not quite. He said wire it to the starter solenoid which is in turn connected through one of those brown wires to the post of the floor. The different is due to the fact the ACR/A127 Lucas/Bosch connector has TWO wires for the higher current rather than one.

Harveys method: Use the ORIGINAL wire for one of the pair. Run a second to the starter solenoid.
My method: Run a new pair to o the battery post through the bulkhead.

Same difference.
 
Not quite. He said wire it to the starter solenoid which is in turn connected through one of those brown wires to the post of the floor. The different is due to the fact the ACR/A127 Lucas/Bosch connector has TWO wires for the higher current rather than one.

Harveys method: Use the ORIGINAL wire for one of the pair. Run a second to the starter solenoid.
My method: Run a new pair to o the battery post through the bulkhead.

Same difference.
Got it. Thank you.
 
The original ignition warning wire is uncut and connected to a short pigtail to the Lucas connector1624890718839.png
 

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It should be noted that 2 wires for this job is a very poor engineering solution. The reason being it can partially fail in a dangerous state. ie. if one of the pair become disconnected, then a single wire would take the full current. The better solution would be to wire the alternator to the battery with the single, heavy cable that runs to the terminal post. The Ford version of this alternator does exactly that with a large, single ring termination on the alternator itself.
 
Be interesting to know how much of the alternator output car potentially go to the battery. Would a 75 amp alternator put all 75 amps through a depleted battery or would that output only be achieved while charging the battery and running other equipment in the car.

With each alternator H Bowers sells you get the bench test print out. At 1000rpm you are getting 20 amps. You only get near the full output over 2800rpm. So to get a full load will be more than the entire P6 electrical system with everything switched on, so it'll need a drained battery for the load and you'd need to rev it quite hard.
 
That works, like me the original cable is redundant then?

Yes, when I do those conversions, which I do on many and varied vehicles I make up my own looms. The only difference with converting from an 11AC is that I would join the 2 wires at the 3AW and use them.
 
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