electrical/starting issues

I have a 1977 Ski Nautique with a 260 OMC engine and I am new to CC. It has always started and ran good for me, but last weekend I could not get the boat started. I was not sure of the problem, but I continued to try to start it, tweaking something different each time without success. Eventually, the battery ran out, so I tried to jump the boat with a car by connecting the cables to both posts on the car battery, and to the positive post and the block of the boat.   The engine turned about a half turn, then went completely dead. None of the gauges show anything when the key is in the "on" position. I do not get any noise, click, or sputter even when trying the key.

I could not find any main fuse that was tripped anywhere on the boat. Everything looks normal, like there are no burnt up wires, no smells, and all fuses I could find checked out ok. I recharged the batteries and the blower and horn work, but still nothing on the engine or dash. The battery reads 12.9V on an electrical tester and the connection to the to the starter and relay or sender (I'm not sure what it is) both read at about 12.8 with the key on or off. I have checked the terminals and main cables, but I don't think the connection is the problem because the problem happened so abruptly.

Next, I checked the ignition switch and none of the three wires on the back were hot with the key on or off. I suspect the problem is power is not getting to the dash, but I do not know where the problem is. Is there a common place to look in the wiring harness that goes bad during surges? What wires go the the dash and where do they start? I should put new cables on it, but where do you start? Do I disconnect from the battery and just pull back to the bilge so I can find where the cables meet the wiring harness? I need help getting power back to so I can work out my other starting problem (carb/spark/starter/fuel delivery).

Let me know if this makes sense or if you need anymore information. Thank you for the help.

I'm glad to hear that I have the engine upgrade and that it was stock...I haven't seen many on the forum that have it.
My boat had a new volt meter just installed when I bought it. I need to trace wires, but the wires in the bilge have been wrapped in a protective sleeve, so it will make changing the cables more difficult. The question I have after poking around is, does the + battery cable first go through the starter, then to the plug/wiring harness? Then the wiring harness splits and goes to other relays, coils, and back to the dash, right? After checking more last night, I think the starter is possible blown, thus preventing it from sending anything past it once the key is turned. Does this sound possible? I pulled the starter and an having it checked out today.

you need to make sure that the nuetral safety switch isn't bad so by pass it on the tranny. Two white wires on the drivers side of the tranny but both on one post. Next you need to check voltage at the ballast resistor, by pass it as well for testing purposes only, then replace the resistor and wire correctly.

But most likely you have a bad connection at the rear of the motor where the wiringharness connector is located back portion of the block drivers side. The battery cables are ran seperately and not part of any harness. all of the wires from the dash go to the connector at the back of the block that the engine requirs all others go to what ever they operate, lights, bilge, blower...

but mess with the connector at the rear of the motor and see if you get 12v at the ballast resistor and 9v or more at the coil.

I am making progress on my problem. I had my starter looked at, and it did need rebuilt. So I had that done, got it back on, and still had nothing the gauges or starting. So I bypassed the relay on the other side of the engine with cables and got a spark and noise. I thought that was the problem and was going to replace it, but figured I should check all angles first so I got under the dash and checked the ignition wires. None of them were hot, so I checked the breaker above it, and even though it did not show that it was blown, one side was hot while the other was not. I bypassed it and tried the key, and I got the gauges and and starter to turn over. So I need a new in-dash breaker. Can I get these at an auto parts store or do I need a marine one? Also, what size should the breaker be? This one is old and I cannot read it. I did not have water around to start the boat, but I will try tomm. and hopefully after I put new plugs and get these electrical problems figured out it will fire right up. If not, I know where to turn.

Thanks again,

It's a 77 so it should have fuses unless someone added a breaker under the dash. A previous post says it has been converted to a volt meter.

24, That is a fuse holder. The cap will 1/4 turn (unscrew) and you will find a fuse inside. If this is the main feed fuse to the dash then it will be a 20 amp. One thing to keep in mind is that fuses don't blow by themselves. Something blew it! Do you have a friend that may be a little more familiar with electrics? You will want to check it out. The holder itself and it's connections look burnt too. Someone has been under your dash without the proper tools and probably the proper knowledge. The .250 Sta-Kon quick connect on the fuse holder isn't even crimped. You need some help before you have a melt-down!!

Thanks for the help, I got the fuse out and it was blown. As for what tripped it, when I was jumping the battery it blew because I connect the - cable from the car battery to the block and there was a bad ground connection on the boat. I have found that connection and cleaned it. My starter was also shorted out, allowing too many amps to flow throught the curcuit. The fuse holder is not balck or burnt up at all, it is just a really bad picture in poor lighting. The quick connect was uncrimped by me to get the wires off because they weren't long ennough to get out from under the dash. Also, I wanted to take it to the store to get new ones anyway. I really don't want to hurt myself or the boat, but I am trying to be safe. Thanks for the concern. Is there anything else I really need to be careful for? I am going to replace the fuse and if it blows again, I will take it to the mechanic. Thanks for all the help.

24, You don't "uncrimp" a quick disconnect to remove the device. Trust me that it was never crimped properly with a crimping tool. It looks like someone took a pair of pliers to it an squeezed. This is not how they work.
The starter current doesn't go through this fuse so that didn't blow it. Something else is wrong. Check for other solderless terminals that have just been squeezed with pliers. Bad crimps with higher amp loads will heat up the connections.

I installed a new fuse with solder and heat shrink and I fixed 2 other connections at the new volt meter with solder and shrink too. Then I put new spark plugs in to make sure I was getting a good spark (they were carbon coated too) and the first tap of the key started the boat right up. This was the easiest start I have ever had.

Thanks to everyone who helped me, you all really know your stuff.