• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Bad Alternator - I Think

Share this page

TheAssociate

TheAssociate

Jedi Hopeful
Offline
Hello, all.

So, I've got a new problem. I was out driving around today, and I noticed the "ignition" light started to come on, then stayed on solid, then went out, then came back on.
Now, the light is out while driving, but will not go out when the car is not running. Stays on all the time with key off.
I have checked all fuses and connections. This is a pretty clean car, the wiring is in very good order.
Also, the battery is putting out 12.75V while running - with alternator disconnected, and 13.79V while alternator is connected. Seems like normal numbers to me, but what is going on here? Is there anyone who has seen this before?

Adam H.
____________________________________________________________
1972 Triumph Spitfire.
 
Sounds like a shorted wire somewhere. Do you have any of the wiring diagrams or a repair manual? You could start by removing one fuse at a time to see when the light goes out and back track on the circuit from there.
 
Anything else on still? Radio, headlights, etc. Just a guess but maybe the switch bad and not completely turning power supply off. Numbers for alternator output sound good. If not switch as Paul says look for a short with wiring diagram.

Well, it's off to look for some comet with the twelve year old named SWAN.
 
O.K.

It was the alternator. I went to my parts guy, got an alternator for $40.00. Plugged it in, like nothing happened.

But, I did learn a lot from an alternator tech at Brians Auto Electric, here in Victoria B.C. He said that the alternator should be making 14.5V, not the 13.7V I had. So, it was putting out power, but not enough - which told him that something was wrong. Also, as I mentioned the light was on when the car was off, and the light was off when the car was on.

I guess the lesson here is, don't reach for the wire clippers just because the light comes on on the dash!

Adam H.
____________________________________________________________
1972 Triumph Spitfire.
 
Hello Adam,

I had the ignition light glowing on my Triumph, but the problem was too high a voltage, the regulatpr (internal - Lucas 17ACR alternator) was not regulating.

So just for information, the ignition warning light warns of over and under charging.

Alec
 
Adam,

Thanks for the info. I never heard or knew of any charge warning light to be able to go on with the ignition key in the off position.
 
[ QUOTE ]
Adam,

Thanks for the info. I never heard or knew of any charge warning light to be able to go on with the ignition key in the off position.

[/ QUOTE ]

If the light comes on when the ignition is switched off, IIRC, this shows that the rectifier in the alternator has failed. One of the diodes would have to short out, which is an unusual circumstance, as they generally open when they go bad. The battery would then discharge through the alternator, lighting the warning light.
 
Thanks for the replies.

Martx-5: You've got it right. That is what the tech described that I could not remember is that one of the diodes had probably failed, and that could possibly make a circuit with the ignition off - which was the case here.

The funny thing is that this has happened to me before - to me it seems common. I do remember the last time(with another Spitfire) about 7 years ago, I went to my garden shed and grabbed a spare alternator, put it in, and that was that - no problem. This time I did not have the luxury of having spare to test with.


Adam H.
____________________________________________________________
1972 Triumph Spitfire.
 
Speaking of ignition switch: Does anyone have a photo showing the wiring on the ignition switch on a 1972 Triumph TR6.
 
Back
Top