Mercruiser electrical drain

[danielz]

I have a '90 4.3 Mercruiser that drains my batteries rather quickly. I'm also not sure that they charge at the rate that they should. When running, the dash voltmeter never gets above 13 volts.
I have traced the problem as far as the 10-prong plug. The drain is on the engine side of that plug and not the instrument side. The wires are all wrapped and I didn't want to dig into them quite yet without some more information.
Where can I look beyond this point? How many things are fed from the 10-prong plug?

 

[chiefalen]

Re: Mercruiser electrical drain

Have you hooked up a external voltmeter to the alt.

Belt tight?

Not unheard of the alt. going bad.

Battery good? How old? Good connections? On tight and clean?

Good cables?

Only you know !

Good luck

 

[danielz]

Re: Mercruiser electrical drain

Have you hooked up a external voltmeter to the alt.
Voltmeter on the batteries while running says 13.5v. Is that high enough?

Belt tight? Tightening the belt last year improved output some.

Not unheard of the alt. going bad. I'm willing to accept that, but want to be sure before I go buy a new one. Also more concerned with the drain problem at this point.

Battery good? How old? Good connections? On tight and clean?
One is new, the other held a charge, out of the boat, for at least three weeks.

Good cables? I replaced the positive cables form each battery and cleaned up connections on everything else.
Yesterday I had both batteries fully charged at home and even ran the engine for a while hooked to a hose, but left the main switch on and by the time we got to the river, neither battery would start the engine.

 

[danielz]

Re: Mercruiser electrical drain

Is it possible that a declining alternator can cause a constant draw on the batteries when the engine is off?

 

[chiefalen]

Re: Mercruiser electrical drain

What could happen is one battery that is bad is drawing down the other.

Take the alternator to a auto store they can test it. Auto zone does it i know.

 

[hard-3]

Re: Mercruiser electrical drain

slow charge each battery individually overnight and have them load tested. take the alternator to a shop that rebuilds automotive starters and alternators and have them load test the alternator. they can load the alternator up to max output and check out for you. may charge a few bucks, but cheaper than a new alternator if you don't need it. most alternators are designed to output 13.9-14.2 volts at operating speed.

 

[John_S]

Re: Mercruiser electrical drain

Please clarify a couple of items:

When you isolated to the 10-pin plug, are you saying you disconnected it and you were still getting current drawn from the battery? and you verified that nothing else was wired direct to battery?

When you say main switch, are you talking about a battery selector switch or the ignition switch?

 

[danielz]

Re: Mercruiser electrical drain

When you isolated to the 10-pin plug, are you saying you disconnected it and you were still getting current drawn from the battery? and you verified that nothing else was wired direct to battery?

Yes, I unplugged it and had no continuity to the ground in the half that goes to the fuse block up front. 3 or 4 of the prongs on the engine side did have continuity, but with the wires all wrapped up, I don't even know what color wires to trace or where they go from there. I was trying to find a schematic online (I saw in another thread that they're pretty much standard in Mercruisers), but with no luck.

There are two positive cables coming off the battery. About the first thing I did was isolate the problem to the one.

When you say main switch, are you talking about a battery selector switch or the ignition switch?

A battery selector. I try to keep it turned off as much as possible too keep from running one or both batteries.

 

[flargin]

Re: Mercruiser electrical drain

Battery good? How old? Good connections? On tight and clean?
One is new, the other held a charge, out of the boat, for at least three weeks.

I had the same problem, it turned out to be a fault in my new battery - yes the new one Check it after giving it a good charge. If it is not 12.6V or better (i.e. 10.5V) you have a shorted cell.

Once the batteries are turned on it will drain both batteries down to 10v in no time, leaving nothing to work with.

Also the short also pulls so much out of your alternator that it cannot get to the the solid charging of 14V. If this is the way it is, watch out for your alternator, it can kill the alternator.

 

[JustJason]

Re: Mercruiser electrical drain

Is it possible that a declining alternator can cause a constant draw on the batteries when the engine is off?

Yep absolutely.
The diodes in the regulator/rectifier section of the alternater can bleed. allowing voltage to slowly ground out.
Its a real common thing actually.
that's one of the reasons we put battery switches in boats.

 

[Bondo]

Re: Mercruiser electrical drain

Ayuh,....

You're Way Over Complicating things,......

Get a Test Light,... Hook it between the Positive post on the battery,+ the other end to the Positive Cable that belongs on that post......

If you have a Drain,..... The Light is Lit.....

Start disonnecting individual components til the light goes Out.... You've then Found the Problem.....

Btw,.....
13.5/ 13.6V is Exactly what is expected.....

 

[scooter4n]

Re: Mercruiser electrical drain

Here is what I did.
I took amp meeter, and took positive clamp off of the battery and put amp meeter one on the clamp one on the battery, so your juice flows tough the amp meeter. key out of ignition.
Now you should see some amps if there is draw.
Now, start taking one fuse at the time and keep checking amp meeter till you see drop or stop in the draw, that will tell you what is drawing. after you done with fuses go to the alt, and so on, keep disconnecting till you find drop.
My draw was old radio, that was taking .25 amp, LOL
good luck

 

[Uraijit]

Re: Mercruiser electrical drain

I had an identical problem. Traced it out to a voltage regulator.

 

[Gazza1]

Re: Mercruiser electrical drain

With that sort or cuurrent draw you should see smoke some where or some very hot cables/wires.
To check the alternator, remove the heavy wire and check there for a current draw with your amp meter.
When you removed the engine plug that suggests that the problem is other than the on the engine.
But I think that I would go with the crook battery somehow