1990 420da alternator wiring…

[KMAS100]

Hi folks,
Can anyone help please…..
I have a 1990 420da with 3208ta 375hp engines. The local caterpillar mechanic here (in Cyprus) has had both engines out along with the gearboxes and overhauled both sets of units. A great job and good work!
However… his helper that assisted in disconnecting the wiring didn’t take note of the alternator connectivity and also threw away ‘a tacked-on bulb’ setup. So we now have no idea what connectivity goes to what on the alternator and where the bulb connected to or even what it was for?
Here’s what we have…
1) Thick red wire coming from the battery isolator
2) Thick black wire coming from the starter
3) Yellow/Green coming from the fuel cut-off
4) Orange wire coming from a cut-off switch
5) Red wire coming from a block connector

The light bulb?.. is this to excite the alternator? How should it be connected and what wattage should it be? Anything else connected to this?
The alternator is a Prestoline. I’ll try and upload an identical picture I’ve found on the internet
Can anyone please advise which wires connect to which terminals and the use and connectivity of a bulb setup?…

 

[hughespat57]

 

[KMAS100]

Many thanks for the response Hughespat57.. I also managed to find that which is really helpful.. if only I understood it!
I presume that the B- would be both the black wire and the yellow/green one?
The Exc connection? I’m assuming must be the excite one but which wire goes to it etc.
Sorry.. I’m not an electrician.. I’m guessing the mechanic isn’t a great one either!

 

[hughespat57]

I am a retired Master HD truck and marine mechanic, but I could not locate a schematic for your boat. So a bit reluctant to say what goes where without testing.

So trace each and be sure what they connect to before attaching.

The heavy red if going to a diode type splitter/isolator should be B+
The heavy black you say goes "to the starter" be sure it is NOT on the battery terminal but on a mounting bolt to the block
Then yes that is the ground to the B- (which is just a bolt to the alternator frame, be sure not to use a long bolt)
Same for the yellow/green USUALLY a ground wire by color but be certain it ties to the grounding bus.
Then yes it also would be the B-

The Exciter tells the alternator regulator to start charging.
If the Orange wire to the fuel shutoff goes 12+ (test light or voltmeter) when the engine is turned "on"
Then that is the Exciter.

The AC tap is often unused, the engine may have a dedicated signal generator for the tachometer.

That leaves the Indicator light.
How this works is one side of the lamp is usually powered 12+ from the igniton/run switch or Exciter.
The terminal will be 12+ when running normally and the light will be off.
But if the alternator stops charging it goes low (ground) and the warning light comes on.

 

[KMAS100]

That’s fantastic….
Ok.. so to make sure I get this right and not blow the alternator charging capability…
1) Thick red wire coming from the battery isolator.. it definitely is an isolator (because it says so on the box), then that wire goes to B+ On the alternator
2) Thick black wire coming from the starter. It comes from the black common terminal on the starter… that goes to B- ground on the alternator
3) Yellow/Green coming from the fuel cut-off, it is the lower connection on the fuel shut-off solenoid.. that also connects to B- on the alternator
4) Orange wire coming from a cut-off switch. So this is a sort of press-to-reset button on the top of the engine. So you are indicating that if this is 0v when the engine start switch on the dash is OFF and 12v when it’s ON.. this is then connected to the exciter terminal. This is the wire that has a bulb connected in series?
5) Red wire coming from a block connector it’s basically a junction block connector on top of the engine next to the press-to-reset button, I’ll have to check if that has 12v permanently or not .. where does that go?
Many thanks by the way… this is a great help

 

[hughespat57]

pictures are worth a thousand words...

cut-off switch? reset? that sounds like a breaker?
need to KNOW for certain if that small red wire turns on and off with the helm switch - test
need to KNOW for certain if the Orange wire turns on and off - test

I am NOT telling you what they do, you need to verify this with a voltmeter or a test light or yeah you're likely to let the magic smoke out of the wires.

Your English is very good so I am assuming English is your native language.

 

[KMAS100]

Many thanks for the update… I’ll be at the Marina tomorrow and check this out (and report back!). Thanks for the English comment.. it’s actually my third language but I lived in Boston and Philadelphia and London for several years.. so I’m quite used to using it.
Thank you again for the assistance!

 

[KMAS100]

Hi Hughespat57,
Some feedback for you…
Ok, I’ve been to the boat today and put the multimeter on the
connections. They are both hot (+12v) all the time. It doesn’t matter if the helm dash engine switch is off or even if the main breaker panel is off, or both of them together.. they are permanently +12v.
One picture is the cut-off switch on top of the engine..
The other picture is the block connector.

 

[hughespat57]

ok, Well not easy
So can you see what the number is on the tip of the reset button, that is a circuit breaker.

Also how many battery banks do you have?
Is the isolator for either engine charging the house batteries?
And each engine has dedicated starter batteries?

Not having even a basic boat diagram is difficult.
Does any of your owner documents have the original basic wiring for the boat?

Take more photos of the isolator, these various wires, everything, anything...

 

[KMAS100]

No problem.. I’ll get some more pictures tomorrow

 

[KMAS100]

Hmmm.. starting to struggle with this now.
There appears to be two harnesses. One goes back into the depths of the boat.. I’m assuming the dash at the helm via a multi-way connector and the other harness really doesn’t have too may wires.. they seem to be initial power related rather than gauges or sensors.
The attachment is a drawing of the traced wires.. these wires are all in the ‘power’ related harness.
I hope you can make something from this.. it shows the x5 wires going to the alternator (which are currently not connected as discussed)
I have checked this drawing several times.

 

[hughespat57]

Was busy all weekend, and this took some thought.
The small red and a large orange should not both go to the same +12v source without different size fuse or circuit breaker.
The small wire would not handle full battery current.

Is the wire to the harness small or large?
It would make more sense if it is small, and both it and the small red should be on the second set of terminals on the connector block. (+12v from the helm ignition?)

See notes on drawing.

 

[KMAS100]

Hi Hughespat57,

many thanks for the latest update.. apologies for the late reply. I have been away sailing for the last week (yes, I venture on the dark side of boating too).
Well in my absence, the mechanic has called in a marine electrician to which they have identified that he has blown-up both alternators!
He has taken responsibility and is replacing them both with new self-exciting units. In fact they must be in by now.. I will go to the marina tomorrow and take some pictures and post them. I assume they are now fitted. I’ll post a further update…

 

[KMAS100]

Hi all, update……
So, the mechanic replaced the two blown alternators and my next task was to fill-up so we can take the boat for a test run (check for oil/ water leaks) and to see if the prop-shafts need alignment.
Started up the boat, all ok… left engines running for 10 mins and drove it round to the filling station… 1,000 litres of diesel later, tried to start it.. flat batteries! Crap!.. now stuck at the fuel station.
Started the generator and left it running for 10 mins which was enough to kick the batteries to life.. got the boat started and returned to the mooring. The mechanic turned up with the marine engineer and they decided that the new self exciting alternators needed a lamp to excite them. Once fitted we can now see a 13.5+ volts being delivered, so charging.
Sea trial is now tomorrow morning.. if all is well I will photograph and document the wiring et al’ and post it in case someone else ever has the same problem… more to come!