Not Charging

[Private Nemo]

Hi, I have twin 1985 Mercruiser 260. One is charging , the other is not . Both have new alternators, and new batteries. The one not charging, I get 3v at the red wire on the alternator. Any suggestions are helpful.

thanks

Drew

 

[makonnen]

Re: Not Charging

With the engine OFF and batteries turned ON and charged... check that you have battery voltage at the alternator stud.

Those engines have a common battery + connection at the starter motor stud, sometimes that connection corrodes away causing an open circuit. But of course, te starter is tucked in an area that makes it difficult to inspect the wiring.

 

[achris]

Re: Not Charging

Hi, I have twin 1985 Mercruiser 260. One is charging , the other is not . Both have new alternators, and new batteries. The one not charging, I get 3v at the red wire on the alternator. Any suggestions are helpful.

thanks

Drew

Unless someone has messed with the wiring there should not be a red wire on any alternator... There should a heavy Orange (from output to main terminal on the starter), a red/purple, which goes to the instrument panel; a purple which goes to the 'ON' post of the ignition switch in the instrument panel; and a heavy black, which is the ground.

Chris........

 

[Private Nemo]

Re: Not Charging

Hi , Yes it has a heavy orange wire going to the starter. Look more red until I wipe it clean. I trace the other wires and they are as you said. But I still am not charging.

Drew

 

[achris]

Re: Not Charging

As Makonnen suggested, battery voltage should be present on the Orange wires. Check for bad connections...

 

[makonnen]

Re: Not Charging

Remember: check fior battery voltage at the big terminal of the alternator with engine OFF batteries ON.

This is because if there is an open circuit between the alternator and starter motor, if the engine is running and alternator is charging, the test light will complete a the circuit to ground and the light will turn on. You won't be able to test for a "real" open circuit.

 

[Private Nemo]

Re: Not Charging

Hi, Thanks for the replys. I think I am just going to run a new wire to the battery, I think that should do it.

Drew

 

[Don S]

Re: Not Charging

The orange wire should run from the alternator to the large terminal on the starter solenoid, not to the battery.
Also check that there is not a square 90A fuse on the starter that the orange wire is hooked to. It may be blown and is why you don't have voltage on that wire. In later years, the orange wire was put on the starter solenoid itself, and the wire going to the circuit breaker was on that square fuse..


View attachment #9 GM V8 All 85-88 399.pdf

 

[makonnen]

Re: Not Charging

I don't know man, I've never seen a fused alternator big terminal.

Yes, the orange wire goes to the starter motor big stud.

Nemo: I would recommend taking a mirror and have a good look at that start motor solenoid stud. If it is in fact corrosion that caused an open circuit then you want to check the other wires. That stud is often a distribution point for battery power.

Dumb idea on a boat I know ... but it works on a car where that stud is easy to see and access.

 

[achris]

Re: Not Charging

I don't know man, I've never seen a fused alternator big terminal. ....

IF the OPs engine has a 90A fuse, then that fuse is on the starter motor stud not the alternator output post. The stud on the starter will have 3 items on it:-
1. Big fat heavy RED battery lead
2. red wire which runs up to the main engine circuit breaker
3. 90A fuse, which has ONLY the orange wire from the alternator on it.

If there is no 90A fuse, then the orange wire ties into the harness on the engine side of the main (50A) circuit breaker.

Chris....

 

[Private Nemo]

Re: Not Charging

Hi, If that 90a fuse is my problem , I would have to pull the manifold to get to it. Would there be a problem if I just ran a new wire from the "Orange" terminal of alternator to the battery. ?

 

[achris]

Re: Not Charging

Hi, If that 90a fuse is my problem , I would have to pull the manifold to get to it. Would there be a problem if I just ran a new wire from the "Orange" terminal of alternator to the battery. ?

As long as it's not going through a battery switch, fine. If you have a battery switch you would need to run the orange to the engine side of the switch....

 

[riptorn]

Re: Not Charging

Check all fusible links for melting. It's doughfull but could have happened previous of buying.

Take out the alternator and have it bench tested.
Could be a 10 amp alt fuse in the fuse panel.(pink or red wire going to the connector 12v with key on)

 

[achris]

Re: Not Charging

Check all fusible links for melting. It's doughfull but could have happened previous of buying.

Take out the alternator and have it bench tested.
Could be a 10 amp alt fuse in the fuse panel.(pink wire going to the connector 12v with key on)

No fusible links on these engines, and no 10A fuse in the panel, and pink wire is for the fuel gauge....

 

[riptorn]

Re: Not Charging

The connecter going into the alternator has to have a fuse some place in the boat. We are talking GM? You need a low current to energize the magnets(windings) before you can generate voltage.

I had fusible links in my 78 Silverline 165 inline. Thought this boat would have the same.
Oh well My two cents worth

 

[Don S]

Re: Not Charging

The connecter going into the alternator has to have a fuse some place in the boat.

What connector are you talking about. Have you looked at the wiring diagram of his engine I posted earlier?

 

[riptorn]

Re: Not Charging

What connector are you talking about. Have you looked at the wiring diagram of his engine I posted earlier?

Sorry Don no did not.
Checking now

 

[riptorn]

Re: Not Charging

What connector are you talking about. Have you looked at the wiring diagram of his engine I posted earlier?

Purple/red purple. 5 & 6
Doesn't show the accessory fuse box in your schematics. Starts after the fuse panel.

 

[Don S]

Re: Not Charging

The connecter going into the alternator has to have a fuse some place in the boat.

You've lost me, the engine doesn't have an accessory fuse panel. I'm asking about the connector that you said goes in the alternator.
There is no fuse in the alternator circuit except the 90A one shown in the diagram.

 

[riptorn]

Re: Not Charging

Sure do look like my older brother.
I'll check if I can find info on the net how the GM alt works. As to post 15