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Triumph TR6 - Ongoing electrical issues!!

Hi Guys,

This is a follow on from a previous thread.

It appeared that the alternator on my "73 was not working. Only 12volts across the battery with the engine running fast. Red ignition light was on.

I replaced the alternator with a reconditioned one from the local LBC shop. Initially all was well with charge indicated around 14 volts. This lasted all of 5 mins and the voltage dropped to 12 volts. Ignition light is on again. Checked all connections and the belt. All good.No burning smell and no fried wires. Everything else electrical works.

What now!!

Also a question about the fuse box. My car has 4 fuses. The top 3 all indicate 12 volts when tested with a voltmeter. The bottom one reads zero. Fuse is good. Is this normal and what does it supply? The wiring diagram that I have shows 4 fuses but only 3 have any attached circuit.

Any help would be greatly appreciated!

Cheers, Neil.
Neil Peniston


The 4th fuse in the fuse box is not connected and should show 0. It can be used for future installation or as a spare.

As far as charging- were you running the engine at higher RPM when you say "This lasted all of 5 mins and the voltage dropped to 12 volts. Ignition light is on again."?

My experience with my car is at idle- the red light is always on but once RPMs go up, red light goes out. Is this what you observe?

As far as voltage goes- I am pretty sure that when the voltage regulator is working properly, it will out put higher voltage until battery is recharged and then drop voltage to meet demand. So the early demand was to recharge the battery following use of the starter motor. Once the battery was recharged- the voltage should drop.

The best check- run it and if after extended use the battery cannot restart the car- then the charging circuit (alternator/ regulator) are still faulty or there is a huge power sink somewhere.

Mike Petryschuk
Michael Petryschuk

Hi Michael,

Thanks for your reply.

The light does go out at higher rev's. However what I understand is that the alternator should put out about 13.5 to 14 volts, thats what all the web info sites say. If I test the voltage across the battery leads at fairly high revs it reads a constant 12.3 volts. However if the ignition light goes out then there is supposed to be no voltage difference and hence no current flow to light the lamp and every thing should be ok.

That's what does not make sense to me. If the alternator is supposed to put out a constant 14 volt and the battery is 12.6 volt there should always be a potential difference and current flow and the light would always remain on.

The second point that I brought up was that on my car there is a fourth fuse. It has 2 red wires on one side and a single one on the other side. This was wired by the PO. Definitely no current flow and everything else seems to work!

I will get the "new" alternator checked again.

Cheers, Neil.
Neil Peniston

Neil- Is it an aftermarket wire or a stock wire?


My two cents advice: I believe it is your new altenator which is faulty.

The fourth wire was probably there as a custom installation for somme accessories.

Speaking of alternator. I was surprised in contryside with a defective alternator to find. this: I went to a small shop repairing alternator to have it fix. The fellow there looked at the alternator. He told me your BL or Ford tractor alternator is broken( I don't remember the tractor brand). He had the same model than Triumph alternator on the shelve brand new.


Jean G.
J. G. Catford

Hi Don,

The alternator is a rebuilt stock unit.

Cheers, Neil.
Neil Peniston

Sorry, Neil, shouldn't have been brief with the question. Are the red wires to the fuse block aftermarket wires or stock?

Hi Don,

I presume it is after market as the car was restored about 10 years ago.

All the wiring has been very well done and the loom has been very neatly wrapped so I am not that keen to go scratching about to trace where the wires go.
Everything seems to be working well except the alternator.

Cheers , Neil.
Neil Peniston

If you have a digital meter ( more accurate ) start the car and put the black probe on the neg post of the battery and the red probe in the back top left of the alt plug ( brown wire on mine ) even idling about 850rpm you should read 14 volts.
Make sure the plug and the 3 wires are pushed in tight, even if you unplug the plug you will read 14 - 15 volts off the terminal on the alt.if not then it's faulty

Charlie B.

Hi Charlie,

That is exactly what I did. I have a digital meter and have measured the out put across the battery terminals and directly at the alternator terminals.

Conclusion, one non functional alternator. So much for it being "rebuilt". I have already talked to the guy at the LCB garage and they will replace it. Hopefully with a better rebuilt "rebuild"

Cheers, Neil.
Neil Peniston

This thread was discussed between 10/05/2009 and 15/05/2009

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