74 merc 115 charging problem

[badbowtie]

I got a 1974 merc 115 2 stroke outboard on my fishing boat. I have one battery running the gas motor and two graphs and aerator. I am using two more batteries to run my 24v trolling motor. I have fished about 2 dozen times this year and never have had a problem till today I put a new gad motor battery last week and forgot one of the wires to hook back up to it which was my onboard charger. I have always gotten lucky that when done fishing I plug the boat in and has charged all three batteries. Since I forgot to hook up one charger wire on gas motor battery it didnt get charged. So I started checking why gas motor was not charging it after I jumped it and found out. I am at 12.0 with boat not running and 12.6 with it running on fast idle at 2000rpm. I am guessing it is stator or rectifier. I thought about just starting with a new rectifier. But from what I am seeing the new rectifier does not look anything like what I got. Mine looks like the picture and iboats says the new one is 18-5707. I am not sure how to check for sure which one is bad.

 

[badbowtie]

Okay I found that was the old part and is crossed to the new ones. So I am going to check and see how to check mine here this morning otherwise I guess I am going to just order a new rectifier maybe first.

 

[Chris1956]

Since the voltage did rise when the motor was revved, the charging system could be working. That charging system is maybe 9A at high throttle opening, and unregulated. Unregulated charging systems have voltages controlled by the battery, which acts like a load.

If you have an ohmmeter, you can check the rectifier to see if it is good.

 

[badbowtie]

I did check the rectifier using these steps and shows it is good but I did pick one up this weekend while was over near the marine store.

1. Place/set your multimeter to the 1000 ohmmeter reading (RX1K, R X 1000, etc). See picture below.
2. Place the RED lead to the ground (G) and place the BLACK lead to A and C alternating. You should show continuity.
3. Place the BLACK lead to the ground (G) and place the RED lead to A and C alternating. You should NOT show continuity.
4. Place the BLACK lead to the terminal (B)) and place the RED lead to A and C alternating. You should show continuity.
5. Place the RED lead to the terminal (B)) and place the BLACK lead to A and C alternating. You should NOT show continuity.
6. If your results differ, then the rectifier should be replaced.

I also checked the two wires coming from the stator tonight and I only have .4 ohms. So I think that means it is bad.

 

[badbowtie]

Well I ended up replacing the rectifier and it is charging know. So I am going to try it this weekend and see what happens.