can anyone tell me a couple of voltage readings: Im trying to establish if my alternator is working ok or not? readings from my car: initally from cold with no electrics: = 12.3 first startup, just engine running = 14.5 engine running with lights,aircon,hazards etc all on = 14.6 then took the car for a drive and after 15 miles lights dimmed and after switching it off the car only just fired up again (starter was clicking) and I just got the 355 home. took readings again with car running in garage and lights on = 11.8 Does this sound like I have an alternator problem ??
forgot to say I have checked the altrernator and : all connections seem good, I have cleaned and reseated them. Belt is intact and seems nice and tight Alternator spins when running.
The 355s, even late ones (mine's a 98) had a problem where they don't make proper ground contact through their mounting bracket. This means that often, the alternator is working fine but still won't charge the battery because there's basically no ground connection from the alternator to the car frame. The solution is to get a good web-type ground strap and connect that from the alternator casing to the frame. I had that done about two years ago and no further problems.
Please fill out your profile with more detail (year of car), but the previous poster is right, cars built before 99 need to have an additional ground cable from the alternator to the motor. Ferrari has one already made up, with termination on each end....and it is cheap...probably less than $15....though you could likely make your own for $4. Just make sure it is of at least 10ga wire. 8 ga would be better still.
Your tests are incomplete and as such have little validity. What you need to test an alt out put is a device that will put a load on it of say 125 amps and see if the alt will keep up. Amperage is what you need to see. You also need to test it AT the battery as in a 355 there are several cable junctions that can cause trouble and what you really need at the end of the day is power going into the battery, not just out of the alternator. Charging systems on 355's are problematic and a test of any method other than I just described is only a false sense of security.
