Mercruiser revival electrical troubleshooting; starter short?

[Capnkirkpatrick]

I'm reviving an old Galaxie with a Mercruiser 470 I/O. The trim wiring seems to have rotted out, but that's my next worry. First I want to try to start the thing. I have a new battery, and besides the main battery cables, there were red and black lines in the battery compartment-both look like they go to different sides of what I think is a starter solenoid (although it's on the opposite side of the motor as the starter, so maybe it's the trim solenoid). Anyway, when I hook those wires up, the battery terminals get super hot. The lead cable connector on the red battery lead to the starter began to melt. I disconnected everything, charged the battery, pulled the rotten trim wires (which I think were shorting things out) and tried it again. Still hot, although I left it on for a much shorter time. So I'm thinking now that the starter might be shorting out? Anyway, I'm looking for a wiring diagram for a 470, maybe one that can explain what looks like it used to be a fusible link to the ignition wiring, and a fuse across the red and black terminals...
I can't tell what color this thing that looks like a fusible link used to be. I think my next move is to disconnect the starter and put a multimeter across it. Should be open, or pretty high resistance, right?
Can anybody point me to such a wiring diagram, or offer suggestions on troubleshooting this system?

Thanks,
-Dave

 

[UncleWillie]

Re: Mercruiser revival electrical troubleshooting; starter short?

Pictures will help in identifying the mystery electrical parts.

A perfectly good starter and a dead short are going to be indistinguishable from each other using a common Ohm Meter.
They will both look a dead short. A good starter motor may have a resistance of well less than 0.01 Ohms.

 

[Silvertip]

Re: Mercruiser revival electrical troubleshooting; starter short?

If there is a fuse across red (positive) and black (negative) terminals the fuse is likely open since that represents a direct short. If that doesn't make sense to you, it is the same as placing a screwdriver or wrench across the positive and negative battery terminals. In other words, "that fuse should not be there".

 

[Capnkirkpatrick]

Re: Mercruiser revival electrical troubleshooting; starter short?

Thank you guys so much for the input! I took a hammer to the starter, and now it cranks reliably. I had one of my sons doing that the other day, but nothing happened. Now either I'm just a lot stronger than the whippersnapper, or my level of frustration is much greater (he gets his out on the XBOX) but after I gave that starter motor a taste of the ole ball peen, he decided to start behaving (the starter motor, not my teenager)! Yeah, I've found out quite by (sometimes spectacular) accident over the years that you generally can't put a short across the battery terminals-and since I couldn't quite figure out where the other end of that fuse went, I never hooked up that part of the circuit. When I started working on it, one side of the fuse was connected to the black wire which was connected from the battery to the trim solenoid (and I haven't traced it back yet, but it probably also goes to the ignition switch), and the wire to other side of the fuse had been pulled out-and I still don't know where that end went. There was something that looked like a match for it-a wire hanging out of the positive battery terminal lead, but as you mentioned, Silvertip, I might just as well have put a screwdriver across the battery terminals as hooked it up that way. Problem is figuring out where it is s'posed to go...I'm guessing it may have had something to do with the ignition or the coil, because now, although I'm cranking, I'm not getting any spark. Still looking for a good wiring diagram, or 470 service manual for what's probably a 1980s vintage MERCRUISER. Any suggestions?
And Uncle Willie-
do I read you right? When you say, "Pictures will help in identifying the mystery electrical parts." Are you suggesting a website I could visit that has pictures of a working system I can look at, or are you offering to try to help with the forensics if I post a picture or two? That's a great idea! Why didn't I think of that!? Now, if I can only figure out how to upload photos to this forum...
-Dave

 

[UncleWillie]

Re: Mercruiser revival electrical troubleshooting; starter short?

... Now, if I can only figure out how to upload photos to this forum...

At the top of the Reply box, The Square next to the Blue Ball with the Red "X" is the "Insert Image" Button.
Easy, Breezy!

 

[Moose truck]

Re: Mercruiser revival electrical troubleshooting; starter short?

Anyway, I'm looking for a wiring diagram for a 470, maybe one that can explain what looks like it used to be a fusible link to the ignition wiring, and a fuse across the red and black terminals...
I can't tell what color this thing that looks like a fusible link used to be. I think my next move is to disconnect the starter and put a multimeter across it. Should be open, or pretty high resistance, right?
Can anybody point me to such a wiring diagram, or offer suggestions on troubleshooting this system?

Thanks,
-Dave

Try this from Mercuiser section; http://forums.iboats.com/mercruiser...utdrives/adults-only-no-exceptions-288430.htm

Leads to; Boatinfo - The library, containing manuals, brochures and other technical documents from the last hundred years!

I'd open the book, but my iPod doesn't do Flash.

On computer now; http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/0
Page 129?; http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/128

For the Drive; http://boatinfo.no/lib/mercruiser/manuals/mercruiser6.html

I hope this helps, Moose

 

[UncleWillie]

Re: Mercruiser revival electrical troubleshooting; starter short?

Thank you guys so much for the input! I took a hammer to the starter, and now it cranks reliably...

I hope you do NOT consider that a fix!
Hitting A started with a hammer does nothing to solve the problem, only the symptom.
The problem will return shortly with Mr. Murphy to assist.
Next time the issue may not be getting away from the dock, but getting back!

The problem may have been bad brushes or a loose connection that you rattled and is still present.
Time will tell.

 

[Capnkirkpatrick]

Re: Mercruiser revival electrical troubleshooting; starter short?

Thanks for the tips. Later I may take the starter apart, but now it's cranking reliably. Sometimes it's just surface oxide that can be knocked loose with the hammer. I may be stuck out in the lake one day, though, or up a creek with a leaky boat and no hammer, thinking what a wise man my ole Uncle Willie was... I am playing it safe in other ways, though. Even though this '78 only has 140 hours on it, and has never seen salt water, I've bought an impeller kit, am draining the oil from the outdrive right now, and hope to install it tonight. I've traced what's left of the rotten trim wires back-they're the ones that go through the transom, and I've been told by different mechanics either 1) I'll have to take the bell housing off, or 2) if I'm skilled, I can run the wires through with fishtape... Any experience with that one? I'm paying $101 for the harness, which should be here in a couple of days. Quotes to install it run around $350 (I have a feeling I'm going to wish I had spent that money). Then it's back to figuring out why I've got no spark...