Engine 1989 Mercruiser 3.7l Model MCM 3.7 Litre Engine SN OC 618761 voltage regulator problem

The batteries do not seem to take the recharge from the generator or alternator (not sure if it is a generator or alternator system coming off the crank shaft at the front of the motor. When the boat is running I can run for hours without a stall out however voltage at the dash voltmeter reads at 11 volts. If I turn the engine off. I get a half a crank out of the starter and it will not start. It seems that the charging circuit is not getting back to the batteries. When I recharge the batteries with a charger the starter motor and solenoid work as they should.
Replaced the ignition switch and the switch fuse cleaned of all wire contacts at the starter motor solenoid, slave solenoid, voltage regulator interrupter switch and battery switch.

What I have done to get a restart after the batteries regained voltage while turned off, was to turn the ignition on and jump the starter solenoid at the red/red /orange to yellow/red. Posts. I ran the engine up to operating temp. Still getting 11.5 v at the dash voltmeter. I shut it down and the same problem occurred. I did heart a distinct click at the slave solenoid.
[h=1]Voltage readings with (ignition on not running)[/h]Battery one 12.0 v this one is new. B Battery two 11.8 v is 7 years old

At ignition switch. red to battery 11.6 v Yellow/red to purple 11.6 v
Dash voltmeter 11.1

Voltage readings at the starter solenoid Engine running
Ignition on not running. Red/Red/Orange to Yellow/Red 11.8 v v
Red/Red/Orange to Copper connector to starter 11.8 v 0 v

Red/Red/Orange

Copper connector to starter Yellow/Red

[h=1]Slave solenoid Voltage readings) Top of Slave solenoid[/h][h=2] Red Yellow/Red

Yellow/Red Purple
[/h]Ignition on not running Engine running
Yellow/red to Red 9.6 v. Yellow/red to Red v
[h=2]Yellow/red to Purple 4.1 v Yellow/red to Purple v [/h]Purple to red 5.5 v Purple to red v

Voltage regulator readings . (ignition on not running)
Top of regulator
Red

Yellow/Red “A”
Yellow/Red Black “B”
Orange
Engine running
Red to Orange 0 v, Red to Orange
Red to Yellow/red “A” contact 0.1 v Red to Yellow/red “A” contact 35.7 v
Red to Yellow/red/black “B” contact 8.8 v Red to Yellow/red/black “B” contact 35.7 v
Orange to Yellow/red “A” contact 8.8 v Orange to Yellow/red “A” contact
Orange to Yellow/red/black “B” contact 8.8 v Orange to Yellow/red/black “B” contact
Interrupter switch voltage (ignition on engine not running 9.8 When triggered 0
[h=1][/h][h=1]The forward /reverse cable from the shifter to the bell housing work fine no resistance either way.[/h][h=1][/h]

Battery 7 years old? fully charge both batteries overnight. Have them load tested at auto parts store,usually free,they want to sell u new ones. Alternator needs 12 volts in to make output voltage. Normal battery voltage is 12.4-12.8. alternator in good condition should put out 14.7 max so not to overload system and battery. Check voltage at battery terminal on alternator,12 volts or a little more?? Do a voltage drop test one lead of dvm on + battery post& other on battery post on alternator reading should be the same. If not bad cable between the two. Remove alternator,have tested at auto parts store. You have the option of a rebuilt or new alternator!

Make sure batteries and alternator, if purchased, are marine. You might do better at a marine store. Most have a battery test facility. BTW... I never get over 5 seasons out of marine batteries, auto batteries ( one boat I bought came with one, don't last that long).

I hope you aren't running with a 1-2-both battery switch in the BOTH position! This is a battery killer especially if there is an age or technology difference between the batteries. Can't open your pix. Did I miss your references/measurements @ a battery switch? Do you have one?

Hi Capt Bob
Determined that it is the voltage regulator that has gone south. I was able to jump start the boat off my ford with it running and charging Engine fired up, with the dash voltmeter running at 13 volts. As soon as I disconnected the car battery. the voltmeter dropped to 11 volts with the engine running. I am deciding whether to go with a alternator conversion or replace the regulator. I am leaning toward the alt conversion kit from Seabreeze
Thanks for your reply and have a good boating season
Cheers Gary

converting is the best way to go

Hi Capt Bob
I did find a regulator for the engine. it is used and I am still contemplating a alt kit from breezeworks. Before I go that route do you know what the voltage output from the alternator on the crankshaft becoming off the 2 yellow/red wires going to the regulator. My multimeter registered 15 and 17 volts respectively.
Thanking you in advance for the info.
Gary

I believe the output from the STATOR is AC voltage not DC. I also suspect it may be pulsed not steady....

Remove two Yellow with red wires from regulator.
Measure Ohms between the two wires...........................greater than 1 ohm stator is bad.

Check one yellow with red wire at a time to one meter lead and the other to ground. If there is continuity the it is shorted to ground
should be OPEN or no reading.

I cannot find a AC spec for stator output........to check connect meter between two yellow with red wires and set meter to AC voltage at least 50 volt setting unless meter is auto sensing. See what you get at 1000 rpms and report back.


Just so you know. The rated output for the original set up is 39 amps.

The replacement alternator kit will have a minimum of 55 amps...........Much better for the whole boats electrical system and for recharging the starting battery!!

That is great info and has helped me a lot going with a alt conversion kit. Do I completely isolate the original alternator at the broken voltage regulator.
Thank You Gary

Make sure your battery is fully disconnected first!!


Carefully remove all connections, follow each wire and remove from end point if possible.

With the exception of the stator wires (which should be taped off (separately) and well and then tie wrapped somewhere away from any moving parts) I believe all others can be removed.
You can also remove the voltage regulator and put a copper or stainless steel tube or even a plastic tube in place of it to connect the hose ends together. This is your incoming water supply!! so getting rid of the regulator may be a good thing and allow better water flow to heat exchanger.


Also I believe the new alt kit is a one wire out put. this will connect directly to where the instructions tell you.

Also with a one wire alternator it may not be charging properly under 1200- 1500 rpms when first started.
They seem to take that many rpms to "excite". But once excited they will charge normally.

Hi Capt Bob
I received the alternator conversion kit from Breezeworks. Do I isolate all the wiring that goes to the voltage regulator?
The alternator is a 3 wire type with harness. The harness has thick and thin red wires that appear to connect to the harness.
The third wire is black with a fusable link and connects to the black wire off the alternator via the bullet connector would I attach this wire to the engine block?Given that the thick red wire is red does it connect to the positive side of the battery?
Thanking you in advance for your guidance on this.
Middlegary

Hello Jack
Apologies for not getting back to you, the advise given answered all my questions I just received the conversion kit fro Breezeworks.
Once I get back to Newfoundland I will get down to fixing the engine.

Thanks so much