Regulator mystery box.

[vegacrank]

I have a 1980 Gulfstar Motor Cruiser with twin Perkins 6.354 engines. The alternator connects to a mystery box shown in the attached photos. One red goes into a wire harness. A black wire goes to the engine. Does anyone know what this box does and how to check it. PLUS: if it is bad: what replaces it? Appreciate any help. Pat
psansieri@hotmail.com

 

[vegacrank]

Thanks Larry will check

 

[Larry M]

It might be a relay. Trace the wires back and see if it goes through your neutral switch on the transmission. He’s a wiring diagram.

 

[vegacrank]

Thanks for the diagram. Will check it out./pat

 

[CharlieJ]

My vote is for a noise suppressor. Necessary back in the LORAN days.

 

[vegacrank]

Thx Charlie. Any idea how to check it?/pat

 

[KnotYet]

Thx Charlie. Any idea how to check it?/pat

If it is possible to open the box, a noise suppressor will have capacitors and/or coils
and chokes.
It probably wouldn't have a high-current relay or heavy duty diode bridge, though.

 

[psneeld]

From a friend.....


It's a MAR120AM RFI filter.

 

[vegacrank]

Thx Guru: do you know how to check if it is working? One comment: when I turn on a 12 volt camera system at the dock, the image is fine. As soon as I start the engines, it goes blank or flashes dark/image. Maybe this is related./pat

 

[vegacrank]

Also: what would I buy to replace it?/pat

 

[High Wire]

Agree with above noise reduction. As a minimum carefully clean up the connections. Doesn’t look like any one touched them in thirty years. Do you have an SSB radio on board? Any other AM type radio? If not then not very useful anymore.
LORAN has been gone since the Clinton administration.

 

[vegacrank]

Googled it and found some on EBAY. Still would like to know how to check them./pat

 

[vegacrank]

Try 40 years Guru! I put PB blaster on connections and will clean up. Any ideas on how to check the MAR?/pat

 

[psneeld]

I would get rid of it if it is just a noise filter/eliminater... I had something similar for the old LORANs onboard...ditched it 8 years/20000 miles ago along with the LORANs.

 

[Swfla]

If knot yet description of parts is accurate, you cn only check the components for continuity, (ohms) and the capacitors for holding a charge. But not for accuracy of their stated values. An rfi filter gives protection from noisy alternators. If you have a SSB radio and there's no static/noise when you engine is running, you have either an alternator that is noise protected itself and or the device is working. Try removing it from the circuit/bypass, maybe that will show noise. There's no simple test/tests for that you can do with a meter. I say. remove it and check all your electronics while engine is running. Chances are, there will be no difference. The device is a non issue from dinosaur era.

 

[vegacrank]

Ok thx all: I'd like to remove them. What to do with connections? ALT + to BAT?

 

[Swfla]

There are several wires in the photos, you've only vaguely specified where two of them go. You need to be very specific on each wire and specifically where they go. "The engine" is vague as is " wiring harness". Just my personal opinion and suggestions, if it ain't broke, don't fix it, 2) it appears that you are leaning toward OCD on this box. Let it go or spend lots of time identifying where all wires are connected. If you burn out the voltage regulator on an alternator, you'll have created a real problem.

 

[vegacrank]

yep: I'll see if I can better describe the wires and ask about bypassing. If they are not needed, I'd rather bypass and remove./thx/pat

 

[High Wire]

To disconnect, look at the diagram in post 8. The dotted line between the filter and the battery gets disconnected at the filter and then connected at the alternator output terminal. Everything else is disconnected. Just lift and tape the other leads where they are until you verify the alternator still charges the batteries ok. Once verified then remove the filter and extra wires.

 

[Swfla]

If you compare the photos posted in #1, you'll see that there's no way to know if it matches or follows the diagram. How do you "just verify the alternator still charges the batteries ok"? It seems more complex than that.

 

[psneeld]

The device doesn't need more wires other than a couple grounds so once the non-diagram wires are identified where they go and what they do....then taking out the device is as easy as connecting the alt positive to the battery or a feed to the battery.

 

[vegacrank]

Well, I took some more photos after work yesterday. It I can label the wires, I'll post as a check. If I recall right that when the alternator is charging ok, you get ~14.4 volts at the battery terminals with no load./pat

 

[Swfla]

Is anyone 110% positive this is a noise suppressor. It has more wires than the diagram of a suppressor. I don't know what it is. This boat is also for sale. Seems to be a risk not worth taking at this time in my opinion. I wish the best of luck in your next move.

 

[vegacrank]

MysteryBox

The attached photos are annotated so I hope it clarifies the wires. Looks to me like that fat wire that disappears into the second harness gets connected to the alternator positive and the others like the ground and wires "1" get disconnected.

(The wiring diagrams for this boat are useless ( I've had them for many years) They are hand drawn and after they got copied 200 times before I got them from the Gulfstar club, they are hard t follow.)

See what y'all think and thanks for all the inputs./pat