1984 228 305 alternator over charging

[yellowbelly]

replaced my alternator due to a bad soaked in power steering one with a new mando 3 wire just like that was on there. now at 2500 or more rpms its jumps in in voltage to 15+ up to 16 then drops back down then it will spike back up. i have eliminated bad batteries the problem still happens with batteries off the other motor. voltage has been checked with a digital voltmeter and dash gauge.ive put in 3 alternators today and same issue. any input would be great my brother owns a stater and alternator shop and hes even lost right now. ive jumped the sense wire to the out put post and im still getting the same thing

 

[alldodge]

Your Red/Purple or Orange (guessing the Red/Purple) wire is not making a connection. With key OFF you should see 12V on the Orange and the Red/Purple wires. With key ON power should be on the Purple wire. If the Red/Purple wire is disconnected, the voltage will spike

 

[Scott Danforth]

verify you have a really good and super clean sense wire direct to the battery

if that isnt it, could be a bad batch of regulators.

are the three alternators from the same batch? if your brother owns a repair shop, have him pull a regulator off his shelf and throw it in one of the alternators.

I personally would remove the mando and install a delphi unit

 

[yellowbelly]

all 3 have tested good on the bench

 

[Scott Danforth]

all 3 have tested good on the bench

then you have an issue with the boat wiring. clean all the contacts shiny enough your kids can eat off them. if the cable insulation is bubbled up, replace the cable because the cable is junk from corrosion.

 

[yellowbelly]

Your Red/Purple or Orange (guessing the Red/Purple) wire is not making a connection. With key OFF you should see 12V on the Orange and the Red/Purple wires. With key ON power should be on the Purple wire. If the Red/Purple wire is disconnected, the voltage will spike

12.7v at both post, key on 12.3v on the excite wire

 

[yellowbelly]

then you have an issue with the boat wiring. clean all the contacts shiny enough your kids can eat off them. if the cable insulation is bubbled up, replace the cable because the cable is junk from corrosion.

im having a hard time on finding where the red/purple wire goes in the harness. maybe ill make a wire from the battery right to the alt and bypass the motor wiring harness

 

[Scott Danforth]

sense lead goes back to ignition switch. so going thru the boat, 4 connections plus key switch at a minimum.

 

[alldodge]

im having a hard time on finding where the red/purple wire goes in the harness. maybe ill make a wire from the battery right to the alt and bypass the motor wiring harness

The Red/purple comes from the 50 amp breaker, but this makes no issue until you measure voltages. Go to post 2 and measure voltages as indicated to verify if connections are working as they should

 

[yellowbelly]

ran a sensor wire right to the battery and its still over charging. i have 12 at the excite wire with the key on, 12 volts at the sense wire and at idle 14.7 at the battery.anything over 3k rpms its gets up to 15.7-15.9 then comes back down the will o up again.ive about lost interest in this boat no after 110 gallons of fuel this week trying to work this out. im gonna try a new ground tomorrow its has continuity right now but one strand of wire will give me that

 

[alldodge]

The going up and down is a bad connection. It could even be on the Orange lead going to the starter post, or the battery cables them selves if corrosion is present

 

[Bt Doctur]

or the internal regulator is going bad

 

[yellowbelly]

update. started following the wires to the starter and i had a few loose connections from me cleaning the motor the morning this all started. 4 days of head scratching and 82 gallons of gas its fixed with a 25.00 part

 

[alldodge]

That is the 90amp fuse, but there is two things that are of concern to me with the state of the part.

The fuse should have blown and then there would be no connection to the ALT output. With no connection the this does explain why the ALT went above 14.5V

What caused it to overheat and burn, was the fuse bypassed with a washer or something?

 

[yellowbelly]

the alt out put was on the small post, the starter to battery was on the stud of the starter and that is what was loose not the out put stud, replaced cleaned all the connections and tightened everything ran 14 miles and it ran and charged perfect . it still had continuity believe or not

 

[alldodge]

OK loose connection