89 supra comp electrical gremlins...

My boat seems to have some electrical issues I can't figure out. My alternator is putting out 12.5ish volts checked with a meter. I've roasted a new starter solenoid and melted the negative battery post on a brand new battery Sunday. Last night I replaced.the battery and solenoid and got it cranked. It was still dragging and not turning over easy. How does the battery receive voltage off the alternator to keep it charged? While it was running I removed the negative cable and the motor died instantly. That means theres no voltage returning to the battery correct...??

The boat has had electronic ignition added as well

If you melted the negative side of the battery, you have a short some where. Check for continuity between + on the battery and ground. Clean and inspect the cable that goes between your negative terminal and the engine. Check the main cable between your + battery terminal and the starter and the cable between the starter and the alternator. Make sure that the cable from battery to starter is fused. Make sure the cable from starter to alternator hasn't melted against the block and is shorting out.

I dont remember there being a wire from the alt to the starter.... Only a ground from the block to - battery terminal, + terminal to starter solenoid. There is a red wire from the wiring harness going to the solenoid.

The red wire going to the starter solenoid is connected to the key and engages the starter when you turn it.

Do you still have the original alternator? It should be connected to the starter solenoid (or perhaps directly to the battery.) Either way, I'd start by tracing the alternator wires and seeing if they are melted or broken some where.

Thanks for the help. Yes the red wire from the switch is connected to the solenoid. I'll unwrap the wireing harness and check for melted wires tonight. Does the altenator chargethe battery through the positive cable coming from the starter solenoid? That's what I can't figure out through eh wiring harness how the battery I's charged...

Does anybody have a good wiring diagram for this boat?

If the engine will not run when you disconnect the battery that means your alternator in not supplying enough voltage, that doesn't mean your alternator is bad it means the engines electrical system is not receiving enough voltage, now think about the melted negative terminal, the battery was supplying all or most of the needed voltage, if that neg terminal was at all loose it could have caused this due to arching. I have to assume your alternator has an internal voltage regulator, usually I see 14.5-ish volts coming from the alternator. I am leaning towards a bad alternator, you can have it checked at any parts store. I do not have a electrical diagram.
There is alot of experience here so keep us updated and you will get the help.

Fran

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Originally Posted by slickscustoms

Does anybody have a good wiring diagram for this boat?

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Does this work? Attachment 12040

There are a few other ones out there. Try googling "351 wiring diagram"

I sent you a copy of the Supra Comp wiring diagram via your email - I hope this helps!!

Thanks everybody. I ordered a new starter and will start working on it again Monday and will keep yall updated. Thanks!!

i installed a new starter from db electrical. now the boat starts easy and seems to be charging {boat runs with ground cable off batt} the old starter had a good bit of water in it....

Glad to hear it's working now, but you don't really want to disconnect the battery while the engine is running, not good for the alternator.

Quote:

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Originally Posted by slickscustoms

My boat seems to have some electrical issues I can't figure out. My alternator is putting out 12.5ish volts checked with a meter. I've roasted a new starter solenoid and melted the negative battery post on a brand new battery Sunday. Last night I replaced.the battery and solenoid and got it cranked. It was still dragging and not turning over easy. How does the battery receive voltage off the alternator to keep it charged? While it was running I removed the negative cable and the motor died instantly. That means theres no voltage returning to the battery correct...??

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The melted negative post is a clue. The area of high resistance is the connection/post area. You may need to repair the negative cable end terminal. The battery post and the cable connection point must be shiny metal clean, no oxidation and no oil or grease.

Check your cables for corrosion. My buddy had similar issues and it was corroded cables and corrosion inside the starter.

As mentioned, I would probably get new cables for the boat. They can be a major headache if they are corroded. Call up an alternator shop in your area, ask if they make battery cables. They may, or will probably know who can. Pulls yours off, take them over and have them make new ones to match. Done and done. Should take you about an hours worth of actual work. And it's very good to do for your electrical system.

If you also change out alternators, look at the GM 1-wire type and run your feed directly back to your battery, or the perko switch with good cable. That will also help get a good solid charge.

Would you still have the Supra Comp TS6M wiring diagram? I'm new here and having electrical probs on my 87. Thanks in advance.

Go to google
Type in “ supra boats manuals”
Open the first link that shows
Scroll down to bottom right
They offer manual for ‘89
Electrical diagram is included near back of manual
Good luck

What is your alternator putting out now? Should be about 14.5v. I replaced mine and still wasn't getting more than 13.2v. Turns out Supra had a pretty lazy way of getting the alternator charge wire hooked to the battery. The 12 gauge wire was spliced into a couple of times before it made it's way to the battery cable at the starter solenoid. A couple feet of 2 gauge welding cable, some solder, heatshrink, and cable lugs gets all the current to the battery now! If you still have a low voltage situation you may want to open the wire loom and see if your charge wire is secure.

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I need the complete wiring diagram for an 86 supra comp ts6 m 351w carbureted

I have one for an 86 Sunsport if that helps.

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