Dead battery 1988 Merc 5.0

[DavieJonesJr.]

Hello everyone,
I got a 1988 celebrity w/merc 5.0 I replaced the battery and took her out all day in lake Michigan no problems.
Just the other day I took her out, and had to jump her to get her started. Ran ok but not quite right. Looked at the volts meter and it stayed at 11.7 and would not go up. So I took her to the dock and pulled the postitve cable and instantly died. So my question is, is it the altinator or can it be a fusable link or somthing else. I know my way around v8's but for some reason I have always had a learning curve in the way the battery hooks up to the altinator and such. Any help would be greatfully accepted, as it is almost time to have her winterized. Thanks.

 

[Don S]

Re: Dead battery 1988 Merc 5.0

NEVER remove the battery cable with the engine running. That will blow all the diodes in the alternator instantly.
Now, you need a new alternator for sure, but it was probably bad befor you did that.

To answer your question, no, there is no fuse. There is a wire (8 Ga. ) that goes from the alternator output to the main battery terminal on the starter. Which is also where the battery cable from the battery attaches.

 

[Silvertip]

Re: Dead battery 1988 Merc 5.0

Popping the battery cable off with the engine running is not a good troubleshooting technique. If the alternator wasn't toast before it probably is now. Remove the alternator and have it tested at any auto store or auto electric shop (aka starter/alternator rebuilder). If it is not working, they can rebuild it. If the alternator tests ok, then you have a cable problem. As for wiring, follow the positive battery cable to find out how its connected. It generally connects to the starter solenoid. The output of the alternator also connects there.

 

[Starflight]

Re: Dead battery 1988 Merc 5.0

My boat came w/ instructions that states "do not disconnect battery while engine is running, as altenator regulator will be damaged". It does seem as if the alt is the problem. Does it have a separate regulator, or is it built into the alt? any how, auto zone will check your alt for free. they just wont have 1 to sell ya if it is a problem. never use a automobile alt as a replacement

 

[Starflight]

Re: Dead battery 1988 Merc 5.0

opps, i was too late

 

[DavieJonesJr.]

Re: Dead battery 1988 Merc 5.0

Thanks everyone. When I bought the boat it came with 1 new Alt, and two old ones. The owner told me several times about fusable links, but never why. That is why I said somthing about it. I still have the new Alt for marine use. So I will check all wireing to and from Batt, Alt and starter. I would also like to ask it anyone can tell me why when I first got the boat the tachometer seemed to work correctly and now it buries at halve throttle? I am begining to think that electrical problems is why I got the boat so cheap!! And as for the pulling of the Batt cable, won't happen again!!! Thanks for everything...

 

[Don S]

Re: Dead battery 1988 Merc 5.0

Be sure you use MARINE electrical parts like Alternators, starters, relays, switches etc. in the engine compartment. They are ignition protected so you don't have a sparking problem should you develop a fuel leak.
Would be a serious explosion, fire hazard.

You tach may be bad, or you may have loose, corroded terminals. Check them all, including the main connection on the wiring harness.

Not sure why the previous owner would talk about a fuseable link, there isn't any on the Merc wiring harness. Perhaps he "Assumed" there was.
One thing to watch for on your battery connections is the battery cables. You don't want corroded cables, loose battery connections loose ends on the battery cables etc. Wing nuts should be outlawed. Use regular nuts and a wrench to tighten the cables after cleaning. Check BOTH cables and BOTH ends of each cable.

 

[DavieJonesJr.]

Re: Dead battery 1988 Merc 5.0

Roger that Don. Thanks alot Im going out to look at it now have a great day..............

 

[DavieJonesJr.]

Re: Dead battery 1988 Merc 5.0

Don, I have looked at the system and all wires seem to be right and in decent shape, so I removed the altenator and compared it to thenew one I spoke of. I will take it to have it tested, but on the back of the new one, the wires are a little different. The old one has 2 wires coming from very back small removable cover, and the new one has only one wire from that cover. Are the rear cover componets interchangable with each other or am I up the river with no paddle, needing to spend a couple hundred bucks? If the old one test bad? After looking at the wiring, One wire goes to the coil then to the ignition module and the other goes to the gas seperator( I think), any ideas????

 

[stevieray]

Re: Dead battery 1988 Merc 5.0

Hey, Davie - welcome to iboats. Looks like you & I have the same boat - is yours a model 230 cuddy? That's what mine is. Sounds like we have the same power package too - merc 5.0/Alpha One.The fact that yours came with "extra" alternators gives me the willys. I would bet it has an electrical issue or two that keeps killing batteries & frying alternators - since you mention the tach problem. You may want to check it out real thoroughly before you put on a new alt. I have not had any electrical problems (knock on teak) & still has the factory setup so I can snap a few pics of the way it was originally installed if that will help you any - let me know.

 

[DavieJonesJr.]

Re: Dead battery 1988 Merc 5.0

StevieRay, I have a 190 openbow. But when I get all the bugs worked out I hope to upgrade to a cuddy or small cabin. I also wonder about electrical issues, like I said I think that may be the reason I was able to get her for 1500.00. Anyway if you want to take the photos that would be awesome. I guess that I am going to have to get a wiring diagram and go through it good. Have a great one......

 

[EarestTBass]

Re: Dead battery 1988 Merc 5.0

Hello everyone,
I got a 1988 celebrity w/merc 5.0.

Looks like I make #3 in this thread! Mine's a '88 Celebrity 20' Cuddy with the 5.0 Merc.
I'm in the process of putting in a switch & second battery. I have noticed that I've got a drain on my battery while the boat is sitting & the battery goes dead.