Thread: Alternator issues

Thanks Coop. That is handy to know. I still haven't got round to replacing mine yet.

THe difference between a AC and ACR is the internal regulator in an ACR alternator.

ACRs have 2 wires coming from the back B+ and IND (which goes to the charge light)
ACs have 3 wires, B+, IND and DF, the last 2 head off toward an external regulator (probably mounted on your firewall) and the charge light.

I only know this cause I've just changed alts from a 15AC 3wire to a 14AC (with internal regulator) 2 wire setup.

Thanks Oz.

Thats weird. If you look at my photos earlier in the thread you can see that my 15 AC only has 2 wires (not 3 like you suggest). It has been like this for years....???

That's the naming convention according to Lucas. All the higher output models the 16,17 18 etc are ACR with an internal regulator. My 15AC is 3 wire with a Bosch RE55 regulator off the firewall, but the 14AC that's attached to my new engine only has 2 wires, so there must have been a change at some point in time but trying to find out any information is pretty hard. The Lucas website is no use for older stuff , most my info came from a MG enthusiasts site

I thought it was time for a bit of an update on this thread.

The repco store recommended the OEX LXA120 as being correct for my 6 cyl 109 GS. This part corresponded to a LUCAS NAB 900 which I ended up purchasing of ebay for a much more reasonable price. Unfortunately however this alternator was too big and the mounting holes were also a different size.

I ended up going to repco to see the OEX 120 which as expected was also too big. The OEX model recommended by Coop in an earlier pic however was a good fit (LXA 119). It is slightly bigger than the old lucas 15 AC but after loosening the lower adjustable mount on the engine I was able to move this into a position where it fit.

The wiring points on the back are not well labelled on this alternator, but I have taken a few pics to show you what I ended up doing. I only had two cable attached to the 15 AC.

x1 cable to B+
x1 cable to IND

Now I have the B+ cable going to same as labelled on the new alternator. There was no IND however so I assumed this was the one I connected it to. The only other point was labelled W, which I believe if for connection of a tacho if fitted.

So now that it is all in and adjusted it seemed to be working fine for the first few minutes and the warning light in the dash had gone out. This however came back on suddenly and wouldn't disappear not matter how hard I revved the engine.

So another problem has emerged somewhere in the charging system. Does anyone have any ideas how I can troubleshoot this? I am not very savvy with motor vehicle electrics and thought bolting in a new higher output alternator would be the quickest fix, looks like there could be other issues also...