Hi, per my Motorola alternator & regulator in the picture attached. Do I have my labels correct in this photo? I believe the 4 wires I’ve labeled are the exciter, the output, the regulator ground and the alternator ground. I’m double checking that my thinking is sound. Thanks for feedback.
Alternator wires
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From my old photos (I took out the gauges as I’m changing some things) the large black wire looks like it went to the ground of the ammeter. that’s why I’m assuming it’s the ground. Also ion the alternator is on the same terminal as what I’m pretty sure is the ground for the regulator. So that would make sense too.
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Originally posted by BenCT View PostFrom my old photos (I took out the gauges as I’m changing some things) the large black wire looks like it went to the ground of the ammeter. that’s why I’m assuming it’s the ground. Also ion the alternator is on the same terminal as what I’m pretty sure is the ground for the regulator. So that would make sense too.
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Originally posted by BenCT View PostFrom my old photos (I took out the gauges as I’m changing some things) the large black wire looks like it went to the ground of the ammeter. that’s why I’m assuming it’s the ground. Also ion the alternator is on the same terminal as what I’m pretty sure is the ground for the regulator. So that would make sense too.
That alternator is not isolated, so most of the time they ground through the mounting bolts to the engine block. Can you trace that black wire? I sort-of-suspect someone may be doing the reverse of what you expect, using that wire to ground something else to the alternator, not the reverse.
The correct way to ground the alternator would be to run that wire to the ship's ground bus or if you don't have one, to run it to the same spot on the engine were the ground wire runs from the engine to battery negative.Joe Della Barba
Coquina
C&C 35 MK I
Maryland USA
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Ben, I've never had an alternator ground wire on any of my boats dating back 50 years or any of the boats I built (100's of them, probably half with Atomic 4s straight from Universal) dating back longer and cars even longer than that No problems that required a redundant alternator ground wire to solve.Neil
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others
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Originally posted by ndutton View PostBen, I've never had an alternator ground wire on any of my boats dating back 50 years or any of the boats I built (100's of them, probably half with Atomic 4s straight from Universal) dating back longer and cars even longer than that No problems that required a redundant alternator ground wire to solve.Joe Della Barba
Coquina
C&C 35 MK I
Maryland USA
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Originally posted by joe_db View PostI have one, but only because my alternator is isolated ground. Other than that, a ground wire is very rarely used.Neil
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others
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I came up with the ground idea as if you see my ammeter photo before I took it apart I’m pretty sure that black wire with yellow heat shrink is one of the wires going to the g terminal on the ammeter or possibly the fuel meter. And in my search for wire diagrams of the model of my Motorola mr12n451d Alternator I came across references to other alternators that looked similar, not the same, but were compatible with westerbekea and they and other older alternators all show a ground in the diagram. So…seemed logical. I may be able to find an old diagram somewhere for this alternator in my old original boat documentation that has been passed down to me from all the other owners of my boat. I will double check in morning.
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Originally posted by BenCT View PostI came up with the ground idea as if you see my ammeter photo before I took it apart I’m pretty sure that black wire with yellow heat shrink is one of the wires going to the g terminal on the ammeter or possibly the fuel meter. And in my search for wire diagrams of the model of my Motorola mr12n451d Alternator I came across references to other alternators that looked similar, not the same, but were compatible with westerbekea and they and other older alternators all show a ground in the diagram. So…seemed logical. I may be able to find an old diagram somewhere for this alternator in my old original boat documentation that has been passed down to me from all the other owners of my boat. I will double check in morning.
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Originally posted by ndutton View PostThat's a specialized condition. As I was watching this thread I got the feeling Ben was being encouraged to chase a very rare zephyr. There's no downside to adding a redundant ground wire, just that no builder or engine manufacturer I've ever run across ever provided one. Notice also that it does not exist on the MMI wiring diagram, their engine rewiring kit, their API alternator or their exchange engines. They do however mention an OPTIONAL redundant ground on their high output alternator instructions.
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Originally posted by ndutton View PostThat's a specialized condition. As I was watching this thread I got the feeling Ben was being encouraged to chase a very rare zephyr. There's no downside to adding a redundant ground wire, just that no builder or engine manufacturer I've ever run across ever provided one. Notice also that it does not exist on the MMI wiring diagram, their engine rewiring kit, their API alternator or their exchange engines. They do however mention an OPTIONAL redundant ground on their high output alternator instructions.
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It sounds like the instruments are grounded TO the alternator, which is not really the best place for that.
Both the 35 and 50 amp alternators that came stock on A4s ground through the case to the engine. They would not have a ground wire added to them nor need one.Joe Della Barba
Coquina
C&C 35 MK I
Maryland USA
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