Rebuilt Alternator

Purchased a rebuilt alternator for my 70 xke roadster (no air) from one of the leading Jag parts distributor. The alternator has an electrical plug/tab on the outside labeled AL which I am not using. Wondering if this connector indicates it is for air conditioning? If so, will the alternator work on my car with no air or is this a problem???. It fits perfectly. Alternator has the number 1112 and remanufactured 109 printed on tape on the outside housing. I noticed after I installed it that at idle 1000 rpms the battery gauge needle was reading higher than in the past… reading on the l of normal near the red indicator on the right side of the gauge. Haven’t taken it out on the road yet. Any comments appreciated. Thanks Ted

Your S2 should have a 3AW unit (under the heater). The AL lug is connected to the 3AW by a brown/yellow wire.

Does your ignition light on the speedo operate as intended?

All 11AC alternators have an AL connection. The early 4.2’s didn’t use the AL tab, because the indicator light was triggered by oil pressure. But all S2’s had the 3AW relay, which requires an AL connection. Is your indicator light working? Is your engine original to the car?

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Thank you! The speedometer is not working correctly. Spinning in place when I drive .

Looking for the brown and yellow wire… Is it under the dash…? Just took the car out for drive after I installed the alternator. Speedometer is not working right… spinning wildly around. Don’t remember this wire you mentioned… but wondering if the wire was hooked up to the old alternator I removed or if for some reason it wasn’t needed on with the old alternator???. I don’t remember seeing the wire.

One end connects to the AL on the alternator:

The other end to the 3AW (looks a bit like a turn signal flasher):

But a starting point might be to look and see if you have a 3AW in place.

Thanks for your comment! I don’t see the indicator light when I turn on the ignition; the car has a Jag Heritage certificate ( matching numbers) so the engine should be original. Speedometer spinning wildly when I drove the car after I installed the alternator. Don’t remember any wires to this AL tab when I removed the old alternator?? Appreciate your thoughts! Best

Geo Thanks so much! Thanks for the comments and the photos… I’ll check tomorrow morning. Won’t get a chance to look tonight but will let you know what I find.tomorrow. The car’s speedometer is spinning when I drove the car this afternoon; I’m assuming this connector is the problem. ?? I appreciated your background/history with e types!! Great story! … I ordered my first XKE roadster when I was on RR in Hawaii in 1969 on leave from Vietnam. I picked the car up new in Queens NY when it came off the boat. An exciting time and a dream come true upon returning from Vietnam. Unfortunately, I couldn’t afford it in my younger days so had to sell it … always regretted having to do that but fortunately I was able to purchase one 10 years ago . Still enjoy just sitting and looking at it. Such a beautiful car! Stay in touch. Best Ted

Speedo spinning has ZERO connection to any alternator wiring.

As Wiggy notes, the speedo is mechanical and operated via a cable driven by the gearbox.

Does actually spin a full 360°? i.e. go all the way around? That is a bit unusual as the typical failure modes include shaky needle, sluggish needle or stuck needle.

I would guess that an speedometer rebuild may be in your future. Several places do this, one is West Valley Instruments in Reseda CA. I won’t mention here where I sent mine but suffice to say I had to buy a new speedometer when all was said and done. I was lucky to find a reasonably priced NOS unit.

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Found the 3AW thanks to your photo. Wire colors are hard to determine due to age and dirt (the 3AW looks like your photo with 3 attached wires and three wires come out of the larger conduit at the alternator… One large one attached with a nut on a post and two smaller ones attached to the positive and negative tabs/connectors. However there is not a fourth wire which appears at the alternator in your photo. So wondering … where is that 4th wire and is it needed?. Not sure it was ever attached to the alternator I removed. Appreciate your thoughts. Best Ted

Erratic speedo Just started after I installed the new rebuilt alternator so that was apparently a coincidence… Over the years occasionally the speedo would bounce but not spin a 360s wildly as it did yesterday. Thought maybe I moved/bumped something under the dash when installing the affect such a dramatic reaction of spinning. Ideas on fix besides removal and rebuild? Thanks again… Amazing support here from everyone greatly appreciated.

The 4th wire is the one from the 3AW - was in the same harness as the others on my car. I suppose you could run a direct wire from the 3AW to the alternator AL. I do not know the effect of not having that wire in place - possibly just a non-op of the ignition light?

Your spinning speedo needle sounds like a broken hair spring based on my limited experience with these. That would require the unit to be rebuilt.

Speedometer has nothing to do wth the alternator. When it spins like this, it usually means that some debris is caught in the magnets. disassembly and rebuild is your only option.

You had an AL wire at some point. A lot of old timers mistakenly believed that the 3AW caused alternator failures, and would disconnect them. So the wire may have been clipped. But it’s somewhere in there. Everything will work fine the 3AW, disconnected, except that the red dash indicator light will never come on.

Thanks Michael. Very helpful comments!! All the best Ted

Ted. I had a similar problem with the speedo on my 3.8. When I opened up the instrument I found that the air gap between the magnet and the plate was too small causing drag and the needle winding up to maximum. I shimmed them apart slightly using aluminum foil as shim material. It has worked fine for the subsequent 15 years.

Shouldn’t you have used aluminium, it being an English car and all? :smile:


Yes. I had actually sourced some on ebay but the extra “i” made the shipping costs unaffordable. We make do with the hand we are dealt out here in the colonies!


Geoff : Love it ! Happy Thanksgiving!

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