I accidentally wired up the alternator incorrectly then started the engine and a smoke came out of the backof it now the alt light stays on have I blown the diode it is a hitachi mounted on yanmar 1gm marine Cheers Glenn

have battery and alternator tested --examine wires --connectors--fuses ---dont just buy and replace parts check and test them

The wire from the alternator may be a fuse link or connect to one. Fuse links protect the wiring harness from going up in smoke when there is a high current short. Get a manual from an auto parts store to find the locations of the fuse links.

Batt probly not chargn cause main wire in back of alt is wornout. Alternator tho sounds bad..it will drain a battery quik.Disconnect batt ovenite to confirm

is the engine running at 800 rpm or more.
if engine RPM is way low the Alternator will die out.
trans light , where is that? name it. exactly
lets focus first on the engine, and RPM
does the dash have a tachmeter, ? yes, then use that.
we keep a hand tachometer (optical , ready for no tach cars)
RPM is everything.... maxwells laws. and such.
1: rpm 800 or more all the time. rule 1, do not skip this.
2: belt to ALT not slipping'
3: battery good. terminals on battery cables tight both ends and
NOT PACKED in green corrosion, .
4: alternator case is grounded good.
5: The connection and ALT, all good.
6: you key on, and the dash charge light must turn on,
if not fix that now, on old cars, the dash light , causes the ALT to self excite, if the lamp burns out the alternator boots up DEAD.
or fails every other car starts. (does)
7: new alt is the wrong alt. zillion wrong ones, only 1 works.

I would make sure the alternator is ok should be reading 14.4 volts at 1500r.p.m.'s make sure the drive belt to the alt. is tight

Start the vech and take of the pos ternimal from battery and if it stays running means the alt is good but if it shuts down the alt may be U/S.Make sure everything is turned off.

Check the small wires that clip into the side of the alternator, they set the Field coil in the alternator and could be causing the issue. Also, how old is the battery? If it's bad the alternator will cook the voltage regulator because it will be at max out put all the time.

HI there
Try checking a few things first like jump start again and then take off the earth lead only{black} and let it run for 6 minute on idle then turn on the head lights main beam ,,if the engine dies in about 2 minutes then the Alternator isent working full power as it should be pumping out 13.5 volts min and the lights should be bright and stay on... if not you have a Alt problem still like a bad feed to alternator or a bad connection on the battery post or a loose wire from engine to body {earth wire } also check out the relay to Alt ..
Let me know how you get on . RON

check the module on the firewall where the wires connect using a circuit light. Also check for burnt fusible links and wires connecting the battery, module, and alternator. A grounding power wire is most likely the culprit.

You have a Bad Belt Tensioner and will need a new one and Possibly a new Belt. Have the Alternator Checked also. It could have gone Bad during these Problems. If the Tensioner is Not keeping the Belt very Tight it will not allow the Alt. To charge the Battery and it will drain very fast.