HELP - intermittent alt light problem on 351 cleveland...OK, this just started tonight and its driving me nuts...started the car, when I turned the key on (but before the car has started) ALT light is OFF - should be ON. When car starts, ALT light is ON. give it a rev, it goes off then comes back. Start driving home, its on for a while, then goes off, stays off all the way home (20 min drive) I then re-start it, same as before , no light on key on but once its started the lights on.. give it a rev, light goes off...so I get the multimeter out, hoping its just a light issue only, but when light is on, its definately not charging - about 12.15 volts - as soon as light is off, charges normally, up around 13.77 volts...

WTF is going on???? any ideas? I don't want to replace alt only to find it hasn't fixed it...

Check the connections for the wiring, both positive and ground as well as the starter motor connections. Wouldn't think the alt was the problem if the light goes out. Off chance but may be the key barrel too.

yeh, been checking wiring connections for the last few hours - nothing seems to change it.. thought I had it just before, started normally, charging, light normal (i.e. off when running) - tried starting a few more times and then it started and light stayed on - gave it a rev and it went off. Took it for a drive, OK for about 10 mins and light came on, not charging and looks like its staying like that...if I accelerate hard it goes off but comes back once it hits cruising speed - I am now really starting to wonder if brushes are worn out...maybe that would explain on again / off again charging and now no charging at all....

Aaargh...what do people think? Am I on the right track or any different ideas??

Worn brushes can cause an intermittent fault as well. Disconnect the battery & remove the regulator from the back of the alt [Two screws black box] brushes should be at least 10mm long. Regards TPVM.

Panel Van Man, you are the man!! Spot on. Pulled the alt this morning, pulled out the regulator, barely 2 mm of brushes showing - put newies in and its now all good !!

Thamks again!!