View Full Version : TR6 Alternator wire?

02-05-2014, 03:05 PM
I just got done putting the engine back in the 72 TR6. When we starting hooking everything back up I noticed a brown wire without connection. I assume it came out of the block for the alternator but can't swear to it. The wire is constantly hot. The car seems to run fine and all the electrics appear to be working. There doesn't seem to be any place in the electrical block to fit the wire. IE: no spades or missing connectors. The wiring diagram is unhelpful to show what is actually wired in there.

Any ideas?


Joe B

02-05-2014, 05:31 PM
Do you have Dan's Schematic?

Does you A.M. work?

Does it have a stripe on it??


02-05-2014, 05:59 PM
No, still haven't bought it but I should next TRF order.

Yes, everything works.

No, no stripe.

02-05-2014, 06:04 PM
It's free

OK Go to the fuse panel and find out if that wire feeds to there

02-05-2014, 08:18 PM
Ah, I thought you meant Dan Master's book.

I have no clue if that wire feeds there or not. That wire feeds into the main wiring loom that runs into the DS fire wall. There is a brown wire that comes out of the main loom (same spot) that feeds into the fuse box.

If you look at the pictures below you can see only two wires currently connected to the alternator. One brown/yellow and a fat brown/white wire. In the second picture you can see where a brown/yellow wire has been cut off on the smaller connector. BTW, the second larger opening in the block does not have a connector in the block. There is a spade on the alternator however. The only other wires coming out of the harness in that spot are for the water temp sender, the oil pressure and the coil.

Anyone have a picture of their alternator wiring block on a TR6?


02-05-2014, 08:26 PM
What I see in the picture is a small brown wire which appears disconnected at the alternator plug. Is that the one that is hot all the time and you aren't sure where it goes?

That appears to be the later Lucas 3 wire alternator, not the earlier 5 wire type. The small brown/yellow wire is for the indicator lamp and the big brown wire is obviously the output which will be connected to a terminal on the starter solenoid (after passing through the ammeter if your car has one).

The remaining alternator terminal should be for the sense wire. I suspect that there is currently no wire on the remaining terminal in the alternator plug and your small brown wire just needs to connect to that open spot.

02-05-2014, 08:29 PM
You were posting while I was typing. Sorry.

The last set of pictures you posted look to me like a conversion has been carried out to use the 3-wire alternator where the 5-wire was originally used. That cut-off brown/yellow would have gone to the second connector used on 5-wire alternators. Your statement that there is a terminal with nothing connected makes me believe this even more. As I said in the last post, it looks like the small brown wire is for the alternator's sense terminal and would fit that open slot in the connector plug.

02-05-2014, 08:58 PM
Well to be honest I have no clue. I bought the car like this back in 96, so it is possible it was swapped out with a later alternator. The strange thing is there is not a spade stuck on the end of the third alternator terminal. Nor do I see where that little brown wire could have been connected to on the large n/w wire terminal. I also just started unwrapping the harness to see if there were two wires cut and still in the harness. I took it down about an inch but didn't see anything. So, anyone have a picture of a three wire alternator setup?!

Attached is a picture of the alternator in my car (wish I could find a part number on it).


02-05-2014, 09:18 PM
Is the gauge in your dash an ammeter or a voltmeter ?

02-05-2014, 09:32 PM
I found the following on vtr.org (and not being in the least electrically inclined) was glad I did:

"Even though the three wire harness connection(s) may be different, they're basically the same in operation. The large brown wire [brown/white on my car?] (# 8 or 10) is the main output to charge the battery. The smaller brown wire (#14 or 16) comes from the harness and supplies battery sensing voltage (if used by the regulator). The small brown/yellow wire goes to the "IND"icator bulb on the dash."

So since my car got hacked I am curious how that brown wire should be set up. Is there a way to know which spade on the three wire is the "sensing" spade? What happens if that wire isn't hooked up? Did the 72 and early cars have an alternator with the sensing voltage connection?

On another note, I assume those other missing wires came out of the same spot on the in the wiring harness the current wires have come out of? The reason I ask is that if I can find them I am going to reattached the cut wires and buy that TRF conversion kit if it is still available.

Thanks in advance.

EDIT: I took a look at the schematic again and I am even more confused. It looks like there are only three wires (72 and earlier) coming from the wiring harness and entering the alternator. The brown, the brown/white and the brown/yellow. The ground I assume are like the other grounds on this car and is provided by being attached to the grounded engine (Correct or not?!) The other n/y wire looks more like a jumped wire on the schematic. However, that doesn't sound right. Also the brown/white wire connects to the ammeter but it is huge. I'd expect the larger wire to connect to the starter. Man I hate wiring diagrams.

Also, leafing through the parts catalog the proper alternator for my car has two spades for connections and the later models (which is what appears to be on my car) have three spades in the alternator. So how is the original alternator a five wire alternator if there are only two bloody connectors?!

02-05-2014, 09:32 PM
Is the gauge in your dash an ammeter or a voltmeter ?


02-05-2014, 10:58 PM
The remaining alternator terminal should be for the sense wire. I suspect that there is currently no wire on the remaining terminal in the alternator plug and your small brown wire just needs to connect to that open spot.

That makes sense to me.

02-05-2014, 11:02 PM
Stick with the 3-wire alternator you have. They are much more common than the 5-wire so when/if you ever need a replacement you will find many available.

The sense wire just goes back to the battery (really to the solenoid), that's why that disconnected wire is "hot" all the time.

I suggest a read over the Moss article in the link below. It says basically to tape off that extra brown wire.

02-05-2014, 11:08 PM
Yes and if you ever go to a 55 amp Bosch it'll be a plug and play>
https://i233.photobucket.com/albums/ee300/poolboy_album/100_0701.jpg (https://s233.photobucket.com/user/poolboy_album/media/100_0701.jpg.html)

02-05-2014, 11:25 PM
I bought a rebuilt Bosch to keep as a spare for all my British cars. So far I've only had one Lucas 5-wire fail and I had a Lucas 3-wire to replace it with. The GT6 has a Delco 10SI and the Mini has a Motorola copy of a Bosch.

Back on topic... I looked at the Advance Auto Wire PDF wiring diagrams. It appears that the 3-wire alternator appeared in the '73 TR6. See the PDF linked below.

What I think is odd about the Moss article is they do not have you do something with the remaining large alternator terminal. Most tech articles on converting from generators suggest that you run a heavy gage wire from that remaining large terminal to the hot terminal on the starter solenoid. Both big alternator terminals are supposed to be capable of supplying output current and the added wire is used to help reduce the amount of current on any one wire. With generator conversions where you are going from say 22 Amps to the alternator's 35 (or more) Amps that is probably more important. I would add a second heavy gage wire to help reduce the current load even though it would not have been "stock" on your car.

02-06-2014, 07:31 AM
The sense wire is there so that the alternator will get a voltage reading closer to the battery or some major junction and not be influenced buy any resistances along the way. Most alternators that have a sense system in them will overcharge if there is no voltage to the sense terminal. How much it will overcharge depends on the system. Usually it's about 1-1.5 volts.

02-06-2014, 08:32 AM
That is another reason I found the Moss article surprising. On other alternator conversion articles, as a minimum they show the sense wire terminal jumpered to the output terminal of the alternator.

02-06-2014, 03:18 PM
I suggest a read over the Moss article in the link below. It says basically to tape off that extra brown wire.
https://www.mossmotors.com/forum/forums/thread/23051.aspx Perfect, thanks! So it isn't a 5 wire system, it is a 5 TERMINAL system. At least the wiring diagram make a little more sense. And here is pdf of those instructions specifically for the TR6 and MGB: https://www.mossmotors.com/graphics/products/PDF/540-280.pdf