Alternator Testing.

[paintman]

I mentioned before that my battery light is illuminated on the Hood but before taking the alternator off I thought I might be able to test it. I found an article on the net on testing them in the U.S.A. They said you should start the engine let it tick over, then remove the earth lead from the battery whilst its still running. If the engine cuts immediately then the altenators knackered!!
Anyone ever tried this way.

['The Gaffer']

I can sort of see the mentality of that test, but personally I would simply put a Voltmeter across the battery, get a fast idle 2000-2500 rpm and look for about 14 volts across the battery.

If 14 volts not there, try another battery first before going down the replacement altenator route.

[gingerpaul]

The battery acts as a bit of a regulator so you might get spikes that could cause problems with any electronics you have. If you're running a carb and distributor set up then it would be worth a go though.

How is the bulb wired in? Is it in the traditional way or do you have a light that comes on when the voltage drops below a particular level? Mine is the later and it will flash on and off at idle and the engine revs change but is off above 1,000 rpm or so.

If a bulb is wired in the traditional way then I think it comes one when the potental difference between the alternator and battery is the wrong way round, ie the alternator voltage is lower than the battery so it isn't working properly. I have never wired one up though so don't take that as gospel. Might be worth a google!

If it is this type then get a voltmeter and see what's going on under there. As Phil says, you'll need to check it at a fast idle, but I'd be tempted to try it at normal idle too. At fast idle it should be >14V and probably about the same as the battery at normal idle.

[paintman]

Thanks for your imput lads! I think i'll start by checking for loose wires and bad earths. The wiring in general looks a bit dodgy. The wiring to the ignition switch under the steering column for example, can be turned off by hitting it with your knee whilst getting in!! I've done this several times...turn key, nothing....wriggle wires and hey presto the ign. lights back on!!  Don't think i'll go to far till I check a few things out on it.

[Furore Phil]

I had an earth strap break on my peugeot once, talks about spikes ! the dash acted like it was possessed, dials swinging up & down, mileometer showing all 8's and all the lights flashing. brown trousers time.

[paintman]

My wife had similar problens once with a Fiat Panda, nothing worked on the car except the engine. On inspection I found this "green mass "attached to the bulkhead! It was the webbed earth-strap loosely clamped with a piece of folded metal!

I prised the strap free in seconds as it wasn't bolted down just folded inside this flexible metal "clamp".  Every bit of the clamp and the strap was corroded . No wonder Fiat have trouble with there electrics!!

I do like Fiats thou...Got my van, both daughters started of with Uno's. I had a Bravo for a few months. One daughter just got a Punto and the other a brand new Bravo turbo!