17 replies to this topic

[Jammy]

My ignition light has started to stay on!! I've been told its either my earth straps or the alternator is on its way out?! When the engine starts the ignition light goes really dim, and gets brighter the more I rev the car?! Any ideas on what is causing this, I've checked the Earth lead going onto the battery terminal but that seems fine, haven't yet checked the engine earth strap, was a bit unsure of where it was, although I'm pretty sure there is one running with the engine steady bar connected to the block on the drivers side.

[Teapot]

When that happened to me the fanbelt had shredded

[tipcat]

If the light goes dim when you rev the car, it's probably not an earth... sorry to say, but your alternator might be on the way out...or you're fan belt is misbehaving. Just by chance, I heard MiniSpares have alternators on sale...

[Jammy]

Hmm, the fanbelt looked ok when I was glancing round the engine bay a while ago, although I didn't really check it out specifically, and I think either Bill or Lee would have noticed a worn fan belt when they re-built the engine a couple of weeks ago. Hmm, I'll look at getting a new alternator then, good dam money-pit!!

(on a side though, what a classic film!! The Money pit! Epsecially where the fire starts in the kitchen and the turkey shoots out the oven!!)

[Dom]

hope this wont effect you from coming to tonights TMF first ever kent meet :saywhat: :gasp: :erm:

[Purple Tom]

almost certainly sounds like your alternator to me matey. I had the same thing on mine about this time last year.

Its worthwhile checking all your wiring too, but for the light to have just come on without any other symptoms, and with the engine out only very recently built, I'd definitely say alternator.

[miniman5]

its probaly the altenater in theory it is, but your batery could be a pile of poo, or all of the things that have been sugestd!

[tipcat]

but your batery could be a pile of poo,

The battery gets charged by the alternator... so if the light gets brighter when the revs are low, it means the battery isn't receiving a good charge... if the battery is 'poo', it'll be 'poo' at high revs as well as low!

[Jammy]

Ok then, next thing, which kind of alternator do you think I should get, I've looked on Minispares and theres a few different ones which different amperages, I'm pretty certain mine is just a standard one (45 amps?!), but then I spotted the full race one at over £200, now I'm not saying I'm going to shell out all that money for one, but why are they sooo expensive?!

[dklawson]

For years the old Minis like mine (Mk1) got by with 22 Amp generators. The early Lucas alternators weren't much more than 30 or 35 Amps. Don't replace the alternator until you know it's bad. When you've confirmed you need one, don't go overboard paying for high-performance or high-output you don't need. You only need more than the stock alternator if you've installed a lot of power hungry accessories.

First, figure out if you need an alternator. Were you over here, I'd tell you to remove the alternator (it's easy to do) and take it to your local parts store. All the larger parts stores over here will check alternators for free using a bench tester in the store. The other way to test your charging system is to make measurements with your volt meter. With the car "off" measure the potential across the battery terminals. It should be somewhere between 12v and 13v. Have an assistant start your car and slowly increase the revs while you repeat your measurement of battery voltage. With the engine running you should measure anywhere from 1 to 1.5v MORE than the measurement you made with the engine off.

If you measure more than 14.5v the controls in the alternator are bad and you need to replace it (too much voltage and you'll boil the battery dry). Likewise, if you measure less than a 1v increase in the system voltage with the engine running, the alternator isn't putting out enough voltage (for whatever reason) to charge the battery and should be replaced.

As for the alternator ground being bad... not likely. If the alternator ground is bad, the engine ground is bad and you'd likely have trouble starting the car... or you'd be melting the control cables hooked to the engine.

[Jammy]

Hmmm, I have an ammeter on my dash, I believe it to read about 8-9 with the engine off, this goes up to 14-14.5 with the engine running, and I'm pretty sure the reading has gone down over the last few days (the reading with the engine off).

[Guess-Works.com]

In theory, the ammeter should show current flow from Battery to car, depending how it is wired... but after starting, there should be a -ve flow of charge, ie the alternator is charging the battery. Once the alternator has replenished the charge in the battery which was soaked during the start, then current flow should return to 0, which suggests that the alternator is now supplying the full current for the running of the car.

A +ve flow of charge shows that the alternator is not providing sufficient current to run the car. When the engine is off, there should be no current flow, unless you have auxillary items which are permanently on. If there is then there is a drain to earth.

[Jammy]

I know it is an after market one, and it only shows a reading once the ignition is switched on, obviously. I think I may buy a new alternator, always handy to have a spare!!

[Guess-Works.com]

Can't dissagree with that, I only have one spare now, as I've had a number of alt's go on me...

[dklawson]

Are you sure you mean an "ammeter" on your dash?

Succinctly, ammeters measure current (flow) of electricity. Voltmeters measure the potential (push) to move the current. Voltmeters are sometimes wired to be "on" regardless of whether the engine is running and may show battery voltage... which as stated before, should be 12-13v. An ammeter will measure "negative" amps during starting as most of the car's power is going to the starter motor. Once started, the current flow should be on the "+" side as the alternator is putting power back into the battery. The current flow (after starting) should initially be high and after perhaps 5-10 minutes of driving (not idling) the level should drop off close to 1-2 amps unless you're running headlights and other high-current drains.

Even if you meant "voltmeter" on your dash, 8-9 volts, this is not good and probably not enough to start your car. Pull the alternator and have it load tested at a shop. If it's OK have the battery load tested. Replace whichever is at fault.