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Old 03-02-2019, 10:02 PM   #1
GB SISSON
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Default Off topic ford alternator question

So... Since I live on an island and have had boats in my early years I picked up a boat from a friend as a project. It sat in the deep woods for almost ten years. Straight inboard, 1992 ford 302 'indmar' marine conversion with fresh water cooling including the manifolds. Among other issues, the alternator was seized. To get that 302 running and pumping water I freed up the alt and used it for just an idler. Well the new marine alternator arrived last week. The old one was a motorola and the new one has exact same terminals. The obvious large terminal 'B' for the battery, and two smaller ones 'S' and 'EXC'. I hooked up the wires the same as before but no charge. The boat is an '82 and has some signs of monkeyshines in the harness. Both of the small wires are purple and the leave the alt and enter a split plastic loom heading twds the rear of the engine. Upon investigation these two wires are spliced together into one purple wire which leads to a terminal block on the rear of the engine. So the 'S' and the 'EXC' terminal are joined at this point. The one purple wire is not hot with ign on or off. I don't see an external regulator, so thinking it's internal. If I abandon this common purple wire and start fresh, what do these 2 small terminals connect to at the end of their path? Battery? Ignition switch? I have done a lot of searching on the web to no avail. That 302 runs quite well now, and gets better each time I fire it up. Would be great to get it charging. Thanks in advance!
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Old 03-02-2019, 10:55 PM   #2
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Default Re: Off topic ford alternator question

I would guess one to the switch, and one to the idiot light which should excite it.
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Old 03-02-2019, 11:27 PM   #3
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Default Re: Off topic ford alternator question

That is a neat boat, it has a lot character. I want one here in SoCal to go ocean fishing but I don't need anymore more projects.

Here are some diagrams for marine alternators. It shows the EXC terminal going to the ignition. I'm guessing "EXC" is for exciter? The "S" terminal is the stator. Ford calls it the stater pulse rev counter for tachometers. I don't know anything about that? I do know that 1965 mustangs used an idiot light wired to the regulator "S" terminal that was also wired to the "S" terminal on the alternator. The 1966 mustangs have ammeters so the "S" terminal was not used. That is what I know about the "S" terminal. It sounds like on marine alternators it powers the tach with a pulsing AC voltage. I think the "S" terminal is the one they are calling the AC tap terminal in these pictures.

I found where somebody wrote this. "Nearly all outboards made in the last 40 years use alternator (stator) driven tachs. The tach counts the A.C. pulses from the alternator. Car tachs counting primary ignition pulses won't work on them". Who knew?

https://www.jamestowndistributors.co....do?docId=1096

https://bpi.ebasicpower.com/charge/alternatorwiring.htm

Last edited by Flathead Fever; 03-03-2019 at 12:18 AM.
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Old 03-03-2019, 12:13 AM   #4
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Default Re: Off topic ford alternator question

cool boat! i agree , big one to battery, exc to the switch. you could try just a quick touch of the exc to hot while running, and you would hear the alt whine when it gets a load
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Old 03-03-2019, 12:30 AM   #5
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Default Re: Off topic ford alternator question

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Originally Posted by Flathead Fever View Post
That is a neat boat, it has a lot character. I want one here in SoCal to go ocean fishing but I don't need anymore more projects.

Here are some diagrams for marine alternators. It shows the EXC terminal going to the ignition. I'm guessing "EXC" is for exciter? The "S" terminal is the stator. Ford calls it the stater pulse rev counter for tachometers. I don't know anything about that? I do know that 1965 mustangs used an idiot light wired to the regulator "S" terminal that was also wired to the "S" terminal on the alternator. The 1966 mustangs have ammeters so the "S" terminal was not used. That is what I know about the "S" terminal. It sounds like on marine alternators it powers the tach with a pulsing AC voltage. I think the "S" terminal is the one they are calling the AC tap terminal in these pictures.

I found where somebody wrote this. "Nearly all outboards made in the last 40 years use alternator (stator) driven tachs. The tach counts the A.C. pulses from the alternator. Car tachs counting primary ignition pulses won't work on them". Who knew?

https://www.jamestowndistributors.co....do?docId=1096

https://bpi.ebasicpower.com/charge/alternatorwiring.htm

Thanks very much for this info! Mine is the first one at the top. Late motorola type. It's a clone to mine. In that diagram it shows the S as a sensor wire to the +terminal on the battery. I had seen a few like this in my search and they had a simple jumper wire from the large B+ output terminal to that S terminal, but no real explanation. When previously running the engine with all the wires removed from the dead alternator the tach worked fine so the tach must be getting it's signal elsewhere. Also, no idiot light as the panel has a voltmeter. Tomorrow I will wire it just like that diagram. I knew I would get the help I needed here. Thanks so much!
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Old 03-03-2019, 12:44 AM   #6
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Default Re: Off topic ford alternator question

My first thoughts are you should repair overhaul the original alternator. Take it to an auto electrician for that job. The" XC" is for exciter which goes to the ignition switch, power when the switch is turned ON. The "S" is the sense wire so that the inbuilt voltage regulator can sense the battery voltage and allow the alternator to charge the correct rate. So in fact your two purple wires connected into one larger purple wire which has to be HOT which you say it is not hot, so make it hot and your alternator should work. There may be a warning light in that EXC wire so check to see if the bulb in it is OK. Follow the wiring along and find out why the connection at the terminal block is not getting hot. Look behind the dash panel at the ignition switch terminals or find a fuse box which might have faulty or corroded fuse connections. It is a boat and subject to damp conditions. Good luck, regards, Kevin.
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Old 03-03-2019, 06:51 PM   #7
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Default Re: Off topic ford alternator question

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Originally Posted by koates View Post
My first thoughts are you should repair overhaul the original alternator. Take it to an auto electrician for that job. The" XC" is for exciter which goes to the ignition switch, power when the switch is turned ON. The "S" is the sense wire so that the inbuilt voltage regulator can sense the battery voltage and allow the alternator to charge the correct rate. So in fact your two purple wires connected into one larger purple wire which has to be HOT which you say it is not hot, so make it hot and your alternator should work. There may be a warning light in that EXC wire so check to see if the bulb in it is OK. Follow the wiring along and find out why the connection at the terminal block is not getting hot. Look behind the dash panel at the ignition switch terminals or find a fuse box which might have faulty or corroded fuse connections. It is a boat and subject to damp conditions. Good luck, regards, Kevin.
14.4 volts! A wire had fallen off of the ignition switch. Since all the diagrams of my type alternator showed the S terminal going straight to the battery and not through the ignition switch, should I run a separate wire from S to the battery? And wouldn't that be a short jumper wire from S to B+?
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Old 03-03-2019, 08:39 PM   #8
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Default Re: Off topic ford alternator question

You could connect your S terminal straight to the B+ terminal on the alternator. What that will do is sense a slightly higher voltage than if it was on the ignition switch and therefore slightly lower the regulated voltage output of the alternator. I would leave it where it was on the ignition switch for the 14.4 volts alternator output. Your boat could do with all the voltage for good operation of extra lights, navigation equipment etc, etc.. You don't want flat batteries out on the water do you ? Regards, Kevin.
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Old 03-03-2019, 11:20 PM   #9
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Default Re: Off topic ford alternator question

Quote:
Originally Posted by koates View Post
You could connect your S terminal straight to the B+ terminal on the alternator. What that will do is sense a slightly higher voltage than if it was on the ignition switch and therefore slightly lower the regulated voltage output of the alternator. I would leave it where it was on the ignition switch for the 14.4 volts alternator output. Your boat could do with all the voltage for good operation of extra lights, navigation equipment etc, etc.. You don't want flat batteries out on the water do you ? Regards, Kevin.
Point well taken... I love how you Aussies and Brits use the term 'flat' for an uncharged battery. Here in the states we call them 'dead'. Flat is just better somehow. Oh, and thanks for the help. We are coming into spring, and crabbing and shrimping is just around the corner. It's hard to describe the look on the visiting grandkids faces when a crab pot or shrimp pot breaks the surface full of wiggling creatures from the sea! Now Grandpa (of seven) has his own boat for when they come to the island for a visit.
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Old 03-03-2019, 11:51 PM   #10
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Default Re: Off topic ford alternator question

I wish I was one of the above posters who had good answers for you, but I'm guessing that once that boat begins to prove its worth, you're gonna have an excessive quantity of smoked salmon to get rid of!
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Old 03-04-2019, 12:06 AM   #11
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Default Re: Off topic ford alternator question

Salmon are a lot harder to catch these days..... This was a great example of reaching out to friends even with something off topic. Thanks all.
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Old 03-04-2019, 12:22 AM   #12
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Default Re: Off topic ford alternator question

14.4 volts fine. With a full charged battery a 12v Alt should put out 14.0v to 14.6v and most consider 14.2 ideal. Above 14.6 or 14.8 one can damage ignition parts and electronic devices.

Yes, still a bit off topic .... I built a 17' ski boat in the '60s and put a Ford 289 (sim to your 302) out of a '65 Mustang in it using an Osco conversion kit (using outside water pick up. The Ford 3-wire alternator and just like the Ford cars the "S" (sensor) was wired to the starter Solenoid to sense voltage at Battery and "Exc" went to dash idiot light. You can substitute the idiot light with a 10 ohm 10 watt resistor, or just hook a light bulb to it. However, for all to work be sure alternator and Exciter circuit are well grounded to the engine block.

The Ford 3-wire Alt is sim to the common Delco 12S 3-wire but likely would need to change pulley and mount .... or use a Delco 10S 1-wire (just won't start to charge until engine rev's above 1000 rpm.

That 302, just like the 289, makes a great marine adaption. For some reason the thrust bearing on the crank is very durable which is important if your boat has a straight-drive marine propulsion set up. With the right prop the boat should really hustle. If you remember the old Chrysler straight 6 cly 100 hp marine engines, they weighed as much as the 289 and 302 which have twice the HP.

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Old 03-04-2019, 07:37 AM   #13
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Default Re: Off topic ford alternator question

When I first looked at your thumbnail, I said "on no" the boats on fire, alternator must have shorted out. I glad you are just cleaning it. I see a V8-60 hydroplane as a future project for you.
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