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Triumph TR6 - Voltmeter pegged

Just when you think it's all taken care of ... a new problem arises. The voltmeter in my car (1974) started swinging from normal to max charge. I will be driving along and the gauge will be reading a quite normal 13.5 - 14 Volts, then it will start to swing toward the upper red, back to normal, up to max and back to normal. This repeatedly happened, in no particular order, as I hurried home.
I can't correlate the event with any other - e.g. while braking, fan on, lights on/off. The weather however was nasty with wind and rain.
Is this my alternators dying gasp or just another mystery short? Why didn't it take out a fuse?
Any ideas before I just replace it with the Bosch unit. Just what is that part number?
I did switch on the blower motor to take some of the extra charge. That extra power sure gets the defrost a blowin'.
Thanks, Steve
Steve Crosby

Steve, mine does that too. Its a 71. I don't know that its a major problem. It just indicates the alternator is charging well, I think. I wonder if anyone out there really knows?

JL Bryan

Hi Steve and John

John your car should have an ammeter rather than Volt? A high swing ammeter is an intermitant high draw or short.

Steve yours is a voltmeter and a high swing is usually the regulation circuit in the alt.. If you have a current draw like a short your voltage will drop not swing up. Your voltage increase will drop the current draw and fans will spin faster lights brighten.

Lots of alternator internals from the transistor to a diode possible? From your weather description though try just blowing out the back of the alt.? Maybe just a wet bugs nest.

Others may disagree but I have seen a bad battery internal short do that as well. Its a basic comparator circuit regulator.

Your in Calgary. Take both the alternator and battery to a partsource store. Either in the car or out. Its free and they can run both load tests and regulator problem checks for alternator. Guys here have an adapter for that alternator?

Regulator is about 5 minutes. Battery load test takes about an hour on bench so look around. There test equipment is all Bear about the best in the business.

Amps do the work. Amps blow fuses. Voltage is the flow. If the voltage push instead of 14 jumps to 20 the amps needed to do the work is low. TR heater works close to normal..:) If the amps drain is high the voltage will go low. Thats when your fuse may blow. Thats a simplification of one of OHMs laws as needed for old cars.


Bill Brayford

Thanks for your insight Bill.
I have the alternator out and will take it over to parts source (canuk-tire) for the test. The battery is a 3 year old Diehard and is in good condition. I didn't mention before that the ignition light remains off during this whole process. Yes, the bulb lights at start-up.
I'm looking around for one of the Bosch model 13017 replacement alternators in the hopes of finding a cheap one before going to the dealer. Really hate to be seen in a Found On Road Dead parts shop.
John, my alternator really makes an alarming whistling noise when on high output. Is yours the same? I'm definitely leaning towards the higher output of the Bosch swap.
As an aside - I took the 7 year old Diehard from my '90 Cherokee in to what used to be Sears for testing. The service guy was only gone in back to run the test for 5 minutes. He said the battery was at 12 volts and dropped to 10.5 under load. His conclusion was that the battery was in good shape. So I went ahead and replaced the alternator (with higher output). I still have the same symptoms as before. Car starts and runs at 14 volts. Gradually this drops to 12. VOM at the battery, when car is running, shows 14 V all the time. I think the battery is hooped as it will not charge over 12V.
Steve Crosby

Bill Brayford wrote:

"Your voltage increase will drop the current draw and fans will spin faster lights brighten."


"If the voltage push instead of 14 jumps to 20 the amps needed to do the work is low."

Hi, Bill,

Well, you got 2 out three right! :) If the voltage jumps to 20 instead of 14, the fan will spin faster and the lights will brighten, and the amps NEEDED to do the same amount of work drops; however, unless you change the resistance of the fan, light bulbs, etc, the current draw will go up if the voltage goes up. The fan and the lights are doing more work.

Ohm's law states I=V/R. Without a corresponding change in resistance, an increase in voltage will cause an increase in current.

I don't mean to be picky, but I thought I'd clarify that a bit.

As a matter of interest, I read the other day that auto makers are considering going to a 42 volt battery instead of the 12 volts we now have. The purpose being to provide the same fan speed, light brighness, etc, that we have now, but at a much lower current. The reason for this being to reduce the wire size, given that modern cars have such a huge amount of wire for all the accesories they now have.

To restate Ohm's law, Power=voltageXcurrent. Double voltage and you get the same power with half the current, as you stated.

Why such an odd voltage number as 42? Why not 48 instead, or some other number? A 12 volt battery actually produces 12.6 volts, or 2.1 volt per cell times 6 cells. For the same reason we call a board that's 1 1/2 X 3 1/2 a 2X4, we call our battery a 12 volt battery. 20 cells at 2.1 volt = 42 volts.

(you already know all this, but I'm tossing this out for the rest of the folks that are not so electrically savy)


Dan Masters

I also seem to recall something about that I squared R thing being related to smoke testing of wires........

A friend at one of the Big 3 OEM spin offs and I were talking some time back about the higher voltage systems. He mentioned that 28 volt systems, a figure that I'm familiar with, were also being looked for automotive applications. He went on to say that it is not just the present day applications, but also the potential for extended use of electromechanical devices. He compared it to the jump from 6 volt to 12 volt systems from many years ago.

Hi Steve

Don't go to Canada Tire same parent different child. Partsource is after the garages and high end hobby rodder types business. You won't find a Canadian Tire tool or item in the store at least not marked.

If there like here crappys test equip. is old and no one really knows how to use. Your Sears guy hooked to a portable and did quick test. Jeeps battery is toast from description running on luck after 5 on any battery. I don't need an analyser for that one. As for the 3 year diehard it probably sits all winter. They don't like that. Dan can probably give a better technical description but in effect if you don't work them they deteriorate faster.

The Partsources here have a full battery load test bench and the test requires about an hour. Thats what I'm going by. You will see a long stainless bench and receive a computer printout if they let you in the back. My nephew is the Bear test equip. rep. and thats what Partsource use here? As its corporate I assume the same all over Canada? Tim feels nothing can get by the equip. if used properly? Canada Tire is a different story in most cases? Nephew by the way is 48 avid car restorer. Knows his stuff not a kid.

Your light comes on if theres power on one side and not on the other when you turn ignition on the battery sends 12 lighting light. When the alternator kicks in turning theres 12 volts on the other side as well. Light goes out. The light does not care how high the voltage is as long as its not zero or in effect a ground path.

Give them the part# they can get any part same as your GM dealer is more than happy to undercut the Ford guy on a Ford part and vise versa. Very competitve business and the parts manufacturers don't care.

Now please excuse me I'm off to do battle with an engineer.


Bill Brayford

Hi Dan and now Steve..:)

OK just an old tech. no engineer. Still use "bad boys rape our young girls but violet gives willingly" for resistors that are visable. Use Ohms only when I'm cobbling. Just one of the guys that makes the device work after the engineering crowd screws up....:) Oh I forgot its the service techs fault that the same device quits all the time. Not under engineering....:)

Interesting on the battery. One of the things I have always advocated is rewiring old cars. As Dan shows its not that hard if folks pay attention.

Most of the old wiring has gone up at least 2 gauges due to patina. Green copper is only nice on roofs. So for those wanting to keep the originals and fight 24/28/42 Volt whatever conversion may be an option as the wire degrades?

Bill Brayford

By the way fellows, that 'FORD' alternator is really a Bosch. It just FITS the 78-80 Ford Fiesta.

I put one on my 73 TR6 as some of you may recall. Perfect fit and perfect plug up. No changes required.

Course I'm the same guy who went with the Crane ignition. Driveablility, not originality. <G>

hope this helps,

Jim Deatsch

"bad boys rape our young girls but violet gives willingly"

In today's politically correct world, it's now:

"bad beer rots our young guts, but vodka goes well"

For those who don't know what the heck we're talking about, that's a means to remember the color code and the numerical values for each code for electrical components.

black = 0
brown = 1
red = 2
orange = 3
yellow = 4
green = 5
blue = 6
violet = 7
grey = 8
white = 9

That is, if memory serves me well. I may have the green and grey reversed - it's been a looooong time since I've tinkered with electronic circuitry.

I'm leaving in the morning for Grand Rapids, MI, and the British V8 conversion convention - anyone else on this BBS going? Should be 50 - 60 little British cars with honking v8s stuffed into them there.
Dan Masters

Bill and Dan et all, thanks for the feedback.
The alternator in the TR is a Lucas 18ACR that gives out 43-45 amps. I believe that is not one of the units offered in 1974, but you never know. (maybe MGB)I just got it back from a rebuild shop and all is well. I wasn't the one who picked it up so I don't really know what was fixed. $75.00 for the rebuild. We were all very surprised that he still had the parts.
While waiting, I checked around for the Bosch 13107, and there are none to be had. Parts Source says try Bosch Canada and Ford says they no longer support or supply that model. I figure the 43-45 amp Lucas is darn close to the output of the Bosch so I'm just going to live with it.
The TR6 Diehard comes into the house for the winter and powers a spare cassette radio in a work area. Depending on use it gets a regular charging from a 2amp charger I bought years ago for a motorcycle battery.
I'm going to flog the Jeep Diehard for a few more miles and then get a replacement. It still starts ok, but I fear for the worst once the snow flies.
All Triumph Drive In is in New Westminster, BC on Saturday. I'll be one of the bystanders - again. I hope to see some of this BBS's members with their cars.
Steve Crosby

Hi Jim Dan Steve

Dead on Dan. Could not remember myself so I looked up. Man that book was musty! Achoo. No I will not be there.

Jim I can't agree more. Functional is better than show. Can you shed some light re: 13107 no longer provided or supported. I would imagine some database has an alternative?

Steve Yep pretty much the same That Bosch and 18. The actual workings of an alternator have not changed all that much. Fella probably looked in his parts tray blew off a little dust and went to work..:)

Powering the vehicle as Jim points out is not a big deal as long as your not looking for spot on original. There are a lot of Boom Boxes powered by some of the wildest alternator hookups known. Theoreticly any alternator will power the car. Thats rodding.

As for the diehard I would alternate them monthly for best performance. Not a battery expert but that works best for my toys. Sort of like the recharge drycells that need to be killed before recharge. I like your shop Stereo sounds like my kind of set up. So your already a rodder? But it will not work the plates like starting and full lights etc. very little amp draw.


Bill Brayford

The trick is not finding the Bosch alternator, the trick if finding one with fan and pulley. As an example, you can get rebuilt by Bosch units without any difficulty, but they do not come with fan and pulley. From a Ford dealer standpoint, these are NLS going back to about 1996-1999 when they stopped servicing the various part numbers (alternator, pulley, fan). This means NOS at dealers will pretty much be impossible to find. Maybe some of the places that sell obsolete Ford stuff (such as Green Sales ) There is also a guy that has been mentioned on this board and he sells on eBay periodically that supplies the Bosch unit with pulley and fan. I have also been told that unlike most, the Beck Arnley rebuilt units are supplied with pulley and fan, but have never confirmed this.

My local non-British parts source got one in for me and rounded up a pulley and fan for it on request to his source as they are not normally supplied to him with pulley and fan. Now he is looking for another pulley and fan so he can do his own car. Also note that this same conversion can be done on 1500 Spitfires and 1500 Midgets. It might also work on late 1300 Spitfires, but again, I have not confirmed this. If you go junk yarding to look for cores or ones to have rebuilt, these Bosch alternators were used on the 78-80 Fiesta and also on the 75-78 Ford/Mercury Capri II with V6 engines. Just make sure that you get the Bosch type and not one of the Ford types, they are not interchangable. There are several sites for searching used parts, this is one I use ona semi-regular basis:

Jim, I do recall you saying that you had to change to a longer belt. I started a thread to see what others had done on this. I had to go 1/2 longer to a Gates 7435, believe that Jim said he went to a Gates 7440, which would be 1 inch longer. These are both earlier cars with the narrow belts. Steve of York said that he went to a 45.5" belt from 44.25" on an mid range TR6 (wide belt, no air pump). Other than the alternator, belt and using an 8mm 1.25pitch bolt for the adjuster, nothing but the parts on the car were needed to make the switch.

The 60 amp Bosch alternator you need is here
Great seller and product; he's put a bunch of these alts up for sale, so availability is not a problem. I've had it on for 9 months now and it works great. You can use the stock belt, but it will be a bit of a struggle.

Rick O.
72 TR6
Rick Orthen

and a great price too Rick O. Mine was $60 with core at my local Parts Plus afilliate.

I went 1/2 longer. That's on a 73 TR6.

The Bosh replacement here in the States comes with pully et al.


Jim Deatsch

I have talked to both Bosch and a Bosch distributor on the AL119X, rebuilt alternator for the above applications, and was told they were not supplied from Bosch with fan and pulley. The Bosch guy even went so far as to say that when they were supplied to Ford for OE fitment, Bosch supplied the alternator, Ford supplied the fan and pulley. I got the same story from an old time Ford parts guy that I know. Beck Arnley units supposedly come with fan and pulley, the one's eBay would have to come with fan and pulley to go along with the bolt on premise. I would imagine that there are some others too, but don't know who they might be right off hand.

According to my handy dandy Lucas catalogs, the pulley for TR5/250/6 applications is the same for 15/16/17 and 18ACR model alternators. Through 75, the fans were the same, 76 fan is 127mm in OD, no dimension shown for the earlier fan, but I want to say that is smaller by about 10 mm. The early Lucas fan has a smaller OD overall and smaller ID than the Bosch unit. The pulley is smaller also in both OD and bore, although I wasn't really that worried about the OD part of it. I looked at the Lucas pulley from a "bore it out and broach a new keyway standpoint" and decided it was a no go. Unless the pulley face was also relieved, the nut and washer would ride into the pulley face radius, not good. If the pulley face was opened up to provide sufficient clearance, you would have some fairly thin material with a high kt and if the high kt was relieved by increasing the corner radius, the material would get way too thin. Maybe a pulley and fan off one of the Motorola alternators used on the TR6 would work, but don't have one around to find out.

This thread was discussed between 07/08/2004 and 11/08/2004

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