Topic

Hi, my MGF MK2 2001 manual 1.8 is having problems. The Alternator is not pushing any voltage from the positive post (shows 11.44v which is being pushed by the battery) so I replaced it. Its still showing same voltage after being replaced with identical replacement alternator.

I've been watching this tutorial to teach me how alternators work. The youtuber explains that voltage from the battery has to be supplied to the voltage regulator for the alternator to work. He then and shows this test to prove that its working. When i try this test on my MGF Mk2 it failed and showed zero continuity.



I've read something different on the forums that says MGF alternators don't need a supply from the battery to the alternator and this DFM plug isn't used on the MGF. Can someone please confirm this is true so i'm not barking up the wrong tree, please?

https://www.the-t-bar.com/forum/9-mgf-tf-pitstop/42828-bosch-alternator

You say that you are measuring 11.4v at the alternator, is this the same as you have at the battery itself? If so, this is pretty low for a battery, so try trickle charging the battery off the car, and then see how the alternator performs. It would be unusual for a replacement alternator to be giving the same problem.
Check the wiring diagrams on this forum to see what wiring goes to the alternator. See community/downloads

Battery has been trickle charged for 36 hours the day before. The battery is new but my cars broken down 3 times in the 300 miles its done since it was installed so has been drained flat each time. Battery could be shagged but its a good brand so the AA thought it should be fine with being full drained a few times. Of course the AA isn't exactly brilliant so feel free to say if you think differently.

To answer your question the battery is a slightly higher voltage but not much more. According to the wiring diagram it goes battery, starter motor, 80amp fuse and then the alternator.

I know the starter motors good because the car starts (battery is strong enough to turn over without the alternator) and i know the 80amp fuse is good because it's not got any burning and it shows continuity when tested with ammeter. SO you can see why i'm stumped as as you said it seems unlikely that a replacement alternator is bad considering it was tested as working before it was posted to me. Thus i'm clutching at straws to try and work out what's wrong.

Edit: Should add the breakdown before the alternator stopped charging was caused by the lambda sensor wire melting into the engine and causing a short which blew up the fuel pump. Mechanic replaced the fuel pump for me. Car ran fine for short journeys (less than 30 miles) for months after this.

Edit edit: had an electrician who used to be a mechanic have a look at it and he's confirmed the replacement alternator is bad. Moral of the story: if the seller tells you they've tested it before posting don't trust them.