Charging issues with 87 Calais Bowrider Mercruiser 3.7

Hey there,

I've had a long string of issues with my boat's electrical system. So I'll give a brief history.

Bought the boat, factory charging system dead. Upgraded to an alternator, installed as per instructions. An electrical short in the dash was burning up the alternators when driving the boat on the water. Had a marine shop find the short but the alternator still runs very hot and the belt squeals terribly when running faster than idol. I suspect another short somewhere in the dash.

My question is what should the gauge cluster pull for amps? Mine currently pulls over 6 amps without any accessories or lights. My volt gauge also reads 3/4 of a volt less than my multimeter attached directly to the back of it. Just looking for some unknowns.

Any insight would be greatly appreciated!
Thanks in advance!

Ditch the amp gauge. Not necessary. All you need is a volt gauge. Can't picture a dash short burning out your alt. I think you are looking down the wrong road.

I used a multimeter for checking the amperage, is a draw of 6 amps for a gauge cluster normal? I burnt up 2 marine alternators before taking it to a marine mechanic and they were literally smoking. I was told by the mechanic that they found a short under the dash and after that it didn't roast alternators in 2 minutes anymore.

It is also worth noting that I have a battery disconnect on it and if the battery is left on overnight it will be dead in the morning. (I've made sure all accessories are turned off) I have also found that there is a 1 volt drop between the battery and volt gauge. I would bet that is my short, where ever it is.

thanks for the help!

Based on your description, I would suspect that there is a short in the wiring harness between the engine and the console. If that's the original harness, at 30 years old it's bound to have issues. Try to find a replacement and test it extensively before installing by making sure that a voltage appied to any one wire does not bleed over to any of the other wires in the harness.

Alternatively, you can make your own harness using different colored wires that you can buy from West Marine or Jamestown Distributors. Try to match the colors used in the original harness. If that is not possible, then write down the color of the wire for used for each function, trying to stick to the Use 14 gauge marine (tinned) wiring.

Here is the link to the typical color codes you will want to use: http://www.marinemechanic.com/site/page101.html

Don't try to power any of your instruments, except gauges, off of the harness or key switch. Instead, run separate positive and negative wires from your battery switch and battery ground to distribution panels under the console. Then run all of your instruments off of those panels - VHF, nav lights, GPS, Horn, internal lights, wipers, etc. etc. Depending on your total load, use either 12, 10, or even 8 AWG if you happen to use a windless. The positive distribution panel should be completely fused.

If you send an e-mail to me at [email protected], I'll send back a typical wiring diagram for a small boat. It's for an outboard set up, but not much different than for an I/O.

One other thought. One way to burn up an alternator is having a bad ground off the battery to the engine block. Are you absolutely sure that your battery ground wire is in top notch condition and is well grounded to the block? If you are operating in saltwater, those ground wires can deteriorate internally - look fine on the outside, but badly corroded inside and will not carry the amps needed.

6 amps is more than 'normal' for a small gauge cluster....see if anything else is wired thru the harness. as suggested in the prior post, nothing should be tied into the engine harness other than your insturments.

The battey dying after an ovenight sit hints at a significant current draw....which you need to eliminate...

I'd be inclined to second the recommendation at a complete rewire after 30 years.....

Thank you for the detailed response!

After tracing more wiring I found a bad connection on the fuse block for the ignition fuse. It gets hot enough to burn your hand and appears to be where that volt is lost with the key on. All accessories are wired separately on the fuse block. The only thing that draws anything significant is the ignition coil.

The grounds on the block are in good condition and I don't believe this boat has seen any salt water. The wiring harness didn't show much for voltage drops and looks to be in very good condition. It may have been replaced by a previous owner.

Thanks again!!

Hopefully, that was the problem. Let us know if it solved it.

Even a cheap alternator is rated at 30 amps... a 6 amp dash draw ( lights on instruments on???) is beneath its notice. Look elsewhere.

OK so this is what I have found.

After a couple days on a 2 amp trickle charger has made a big difference. I have had a battery maintainer on the battery off and on over the winter to keep it charged. Although it checked out with a load tester and had the power to start the engine, it is clear that it still needed a few days on charge before running the engine. The Alternator runs much cooler now.

In addition, with the bad connection in the fuse block fixed and all contacts cleaned, the dash voltmeter reads far more accurately and the charging system dummy light doesn't stay on. The bad connection read 12.5 volts with the key off and 10.8 with the load of the key on.

I have yet to take it out on the water to see how it performs, I will be sure to update after I do.

Thanks again for all the help. Chawk_man, I will be sure to message you, a wiring diagram is always valuable. Thanks!