Help identifying sensors on 3-way combo block

[Kyle Routh]

I am about to start the fuel cooler removal on my 6BTA, but my 3-way combo block has an extra sensor that I don’t understand the function of and I’m not sure if the other sensor is even hooked up correctly.

I have attached four pics:

#1 is a close-up of the combo block with the various sensors labeled as best as I can.  Sensor “B” looks like the oil pressure sending unit except it only has one wire going to it and only one connection point on the sensor.  Also, you will notice the harness going to that sensor actually has two wires – but one has been snipped off (labeled on photo).  Is this right?  I don’t understand why one wire is snipped and only one wire is running to the sensor.

Also on that pic, sensor “A” has two connections going to it.   One is labeled “Trans Press Sender” and runs into the main wiring harness but I don’t understand why a transmission pressure sender would be plumbed into the oil pressure gallery on the combo block?

The other wire attached to sensor “A” is not labeled but goes up to another sensor that looks like it is screwed in right at the No. 4 cylinder (as counting from front to back).  Photos #3 and #4 are of that sensor – one close up and one far away.  I am not sure what that sensor is for, and why does it’s wire run from the No. 4 cylinder back down to the 3-way combo block onto another sensor?

Maybe this all make sense to someone – but I don’t understand what I am seeing.  Any help would be greatly appreciated as I want to get this cooler deletion going and clean up this craziness!  🙂

Thanks in advance!!

Kyle

Topic

[Kyle Routh]

Thanks Tony.  Yes, that neutral safety switch photo is actually the one I uploaded from my transmission.  🙂 Since my transmission has no pressure switch or sender, would it make sense that they might reuse the transmission pressure sender wiring and connect it to the oil pressure switch just to get the alarm signal up to the helm? (see photo attached)  As Rob mentioned previously, Carver went with a case grounded system so I am finding the ground wires have been snipped off.

[Tony Athens]

Neutral safety Switch wires

Two pics attached  

For maybe 20 yrs, Cummins used a white ( from the gauge) & black (gnd) wire in the factory harnessing for the gear sender

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Kyle Routh

[Kyle Routh]

Follow-up, thoughts and a question or two.  🙂

I went to the boat and searched all over the transmission for additional connections for the “Trans Press Sender” but there were none.  I saw the photos on your site of the typical connection points on the transmission or gear cooler, but I have no connections at either of those locations – or anywhere else.

I then found the following link from your site that has a photo of the exact wires for the “Trans Press Sender” in question.  It doesn’t show where they go, but it seems they are a part of the harness:

Cummins Mechanical Engine On-Engine Gear Pressure Sender Wire Location

So what I started thinking, since I don’t seem to have a transmission pressure sender or switch, maybe they used those wires to connect to the oil pressure switch, which is also daisy chained to the coolant temperature switch/sender.  I do not see a dedicated wire running to the oil pressure switch so maybe this is how they used those wires?  

Finally, I remember seeing on your site a side view of a 6BTA showing all the oil ports but I can’t seem to find it.  But I wanted to verify that the ports in the attached photo are correct to use.  This was taken from the “fuel return cooler deletion” video so I know the one he’s pointing at is a good location for the sender, but I wanted to verify the other red-circled location would also be a good spot to put the oil pressure switch.  I may opt for the leaving the small oil line that ran to the old combo-block installed and connect the pressure sender to it as shown in your article on switches and senders, but I need to see which installation location gives me the best access to the seawater pump/impeller.

Thanks again for all the help!

Kyle

[Rob Schepis]

Good stuff — you are off and running now!

[Kyle Routh]

Great info – thanks for linking your article in your reply!

The whole idea of daisy-chaining (i.e. paralleling) the switches makes perfect sense and that would explain a lot regarding my setup.  As your article mentions, this does not help with identifying the specific fault since any one of them will set off the common alarm – but at least they are being monitored.

Plus understanding now about Carver being case grounded vs. floating ground helps too!

Lots to consider – I like the idea of having individual lights with a common alarm like the SMX Deluxe Alarm Panel – although it is out of stock currently.  But that will give me time to dig in and chase down what I actually have and ensure that they are working correctly.  As you can see from the pics, the previous owner let the corrosion go unchecked, unfortunately.

And thanks for the tip on chasing down other connections on the transmission!  The only pic I have is of the transmission-in-neutral connection (attached).  (You gotta excuse all the flaking paint – again the previous owner didn’t really stay on top of these things.  I have since scraped all that mess off!)  We will be back at the boat next week so I should be able to see what other connections might be there.  Time to get out the multimeter and go to work!

Thanks again for all your input and advice!!

Kyle

[Rob Schepis]

Read this, it will answer your Switch vs. Sending Unit question and hopefully much more: https://www.sbmar.com/articles/redundant-alarms-least-expensive-engine-insurance/

Cummins OEM was a floating ground, thus the two terminal oil psi sending unit (your label B).  Carver is one of the builder’s that re-invented the wheel as to instrumentation and their wiring setup is case grounded, so only the signal wire on sender B as ground is through the threaded connection and via the engine block.

The oil switch is your label A.  This is either open or closed to ground (read my linked article).  What I believe Carver did was interconnect (daisy chain – I covered this in my linked article) multiple switches together into a single alarm (warning light or buzzer).  That would explain the two wires on your oil switch labeled A with a connection to the coolant switch in the head that I identified earlier.  I bet ya a six-pack that the wiring  label Trans Press Sender is actually for a trans pressure switch.

Check the tranny for a pressure switch and trace the wiring back to the combo block or do a continuity test from what you find at the tranny to either the oil switch or the coolant switch,  Got any good pics of the tranny? 

And be sure if you replace any “sending units” they are matched to your gauges.

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Kyle Routh

[Kyle Routh]

Thanks Rob!  Just learning about the coolant port was a step forward!

No custom alarm panels – just a pretty stock 2002 Carver 396 with twin Cummins 5.9 6BTA 370HP Diamond.  I’m the 4th owner.  Either the first or second owner put some effort into the engines by doing the remote oil filter on the starboard engine and a remote fuel filter on the port engine – so all my on-engine filters are in the middle and easy to access!

I also found a Seaboard aftercooler/heat exchanger kit left onboard.  I have not got to those yet but they are on my list.  🙂

I am going to replace that oil pressure switch but I notice the ones y’all sell have two connectors and are called “senders” and not a “switch”.  Maybe it’s just a terminology thing – this is all new to me.   What’s the difference between an “oil pressure sender” and an “oil pressure switch”, if any?

Any concerns with that oil pressure switch only having one connector and the other one snipped off?  Is that how they used to wire them 20 years ago?  I am guessing I can just add a connector to the snipped off wire and bring both wires to the new pressure switch?

Thanks again!!

Kyle

[Rob Schepis]

The work of a boat builder, prior owner, etc, certainly not Cummins as I’m sure you are already aware of.  A is a pressure switch, B is a sender and photo 4 is in a coolant port on the head (temp switch or sender)  No clue as to the trans press labeling.  You have some digging to do as to disconnecting, tracing and figuring out what does what…   Do you have custom alarm panels or is this one of the builder’s like Bayliner who did their own thing?

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Kyle Routh

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