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My exciter or field wire isn't working going to the alternator but I can excite it by bring 12V to the alternator using a test wire. I understand that the ignition key is to send this 12v signal but it aint workin so that's why I do it with a test wire at the alternator plug (3 wire). My question is can i branch off the oil sender and connect it to the alternator exciter plug as a fix? Or is there another better fix? I've tried to chase the wire and it's nearly impossible around the engine and once it goes to the helm it's lost in a pot of spegetti. I do see a cummins electronic panel but no idea what I'm looking for? Could it be a wire going directly to the ignition key?
Any sugestions guys?

I abandoned the exciter wires on my 6BTA alternators (they are standard Delcos) and use the old "one wire" system with just one wire off the big lug to the battery. So in theory it is not "self exciting" and you have to race the engine up to about 2200 rpm for it to excite, then once its excited, it will continue to charge even at idle all day, and usually retain enough resudual magnetism to self excite overnight.

One of those things that sorta "ain't worth the trouble".

UV

More than likely the diode is open that feeds the field circuit in the harness.

Yes you can feed it thru an oil pressure switch. Make sure its fused, field circuits run about 3 amps@12vdc. Also make sure you use boots on the switch connections as they will be hot.

The single wire Delco units use residual magnetism to excite which is why some times you have to rev the engine above 1k to get them to kick in.

okay...thanks for the suggestion Bruce. Concerning the diode, would that be independant of the Cummins circuit board or is it integrated on their board? Just trying to figure out where to look for the problem before I go to the alternative oil pressure switch with your fuse and boot suggestions. Thanks again...

Feel the exciter wire. There is a small multi colored (striped) diode that is soldered in. The connection is probably broken. I peeled back my insulation and removed it. Note (on paper so you won't forget) the colors and their direction towards the alternator. Take the diode to Radio Shack and they'll probably match it. Carefully re solder the new diode in place and slip a piece of shrink tubing loosely on the wire. Crimp on a lug and connect to the alternator. If all works as it should, heat your shrink tubing. It's fixed.

I'll look for the diode but do you have any idea where i should start looking? Alternator end or where does the other end begin I'm guessing at the ignition? Any suggestions?

The diode is right before the lug you would use to connect the wire to the alternator. Looking at the wire, you would swear it's not there as it's covered with insulation exactly like the rest of the wire. If you have a long enough exciter wire strip back 2-3" starting at the lug. The diode on mine was so small there wasn't even a bulge in the wire. I cut it open because the wire felt like it might have had a corrosion break in it. Didn't even know there was a diode in there until I opened up the insulation. It is tiny. looked like a piece of striped candy with a short piece of solid wire coming out of both ends, and one of those wires was broken with no room to resolder without roasting the diode.
I went to Radio Shack and was surprised they even knew what it was. A good alternator rebuilding shop probably would. Good luck.

Walter, thank you for the detailed explanation. I'll start looking next week for the dreaded diode. I'm heading up your way this weekend for early season fluking off of Montauk. I will post again once I get the problem solved.

Someone here might even know the specs or name of the specific diode.

Looked for the diode and no luck locating it. So I'll try using the oil pressure switch to excite alternator. My question is do I connect each hub of oil pressure switch and bring each wire to the alternator spade connection to create the circuit to excite the alternator?

The oil pressure switch will have two terminals.

To keep it simple one connection goes to the field the other is the feed from the + battery connection on the starter. Makes sure it is fused close to the source always. Use boots to cover the connections at the switch.

Don't take the short cut and loop a wire from the out put of the alternator to the switch to the field. You can have issues with the alternator regulator kicking in and out.

Bruce- am I wrong that the diode is normally just after the lug fitting that connects to the alternator? Mine (both) were pretty much camoflaged and looked like part of the wire. I suspect anyone not knowing what they looked like and where they were would never find them on their own. Is that their normal position?

I gave up replaceing diodes. I had 2 in line, type N501.I, if you want to try replacing them. I ended up running power from my start (key) switch. Was able to pick it up power in the engine box terminal strip. I have had no problems with back feeding into my start circuit. My oil switch is fail closed, so I could not come off of that. Like Walter said, the diodes were on the wire connecting to the exciter lug -- about 1 foot back. Look (or feel) for shrink wrap -- the same color (yellow), as the wire -- hard to see.

Note that the exciter wire has to be on a switched circuit, exciting the alternator only when your engine, or key switch is on. Otherwise it will constantly draw down your battery.

Requesting clarification based upon Bruce's suggestion: If the oil pressure switch is operational prior to using it for exciting alternator then do I add a wire from 1 treminal of the oil pressure to the field (exciter) and then from the other terminal of oil pressure bring wire from starter + positive battery comnnection. I think I got it but please confirm. Since oil pressure switch is operational I'm interested about bring the + pos. started from starter. Is this correct?

You are correct.

Make sure the wire from the starter + is fused just a short ways from the starter connection. !4 gauge wire and a 5 amp fuse should work as field circuits draw about 3 amps.

Also pressure switches come in two flavors, "0" pressure - connection open what you want.
"0" pressure or low pressure connection made for an alarm circuit.

Use an ohm meter to confirm what switch you have if your not sure.

Bruce, thanks for the explanation. I will work on it this weekend and let you know how it works out.

So I'm trying to get this sorted out. I want to buy a new switch and it's 1/8" pipe fit size. I will need a 2 terminal pressure switch. My question is do I get it as normally on or normally off?

An oil pressure switch to energize your alternator field should be normally off (normally open). When your engine and oil pressure builds, the switch will close (turn on) -- sending voltage to your alternator.

An oil pressure switch for an engine alarm, typically, is normally on (normally closed). When your engine has oil pressure, the switch is open. When pressure drops, the switch closes and sounds your alarm.

--Marshall