CIH 1660 - more on oil gauge

The oil pressure gauge needle is full over to the right. I disconnect the wire at the sender. I turn on the key...this makes the gauge needle flutter a little. I touch the wire to ground and either get no effect or a slight flutter of the needle. I removed the cover from the gauge unit and slipped the unit out of the dash and removed the plug. Not sure which wire in the plug is the one for the oil unit so I could not check continuity on the wire. The gauge slips out and you can see on the back there are three pins that are the electrical contacts for the gauge. None of them are marked. This is as far as I got. I am assuming that the gauge has a power supply and ground and that the third connection is from the sender and somehow moves the needle. I am going to ask my service guy to fax me a schematic of the engine harness and instrument cluster. Failing that I guess I can hook my meter to the wire at the sender and then test ALL the contacts in the harness and see if any of them get a reading. Still won't know how to test the gauge to see if it works. At this point I might just replace everything with new and see what happens.

When it comes to combines and wiring there are them things called RATS < MICE and Chipmunks . So for one we know the gauge is toast and as for the wires , well ya start tracking them down and look for rodent chew or anyplace that they maybe pinched . Next would be a new sender . As for find a good mechanical gauge good luck with that unless ya can raid and old big truck junk yard and get a real gauge , then comes running a metal or plastic line and the plastic would not be my choice . steel brake line or copper with a flex steel line off the engine and up into the dash off the solid metal .

You are correct on what the three connections on the gauge do. You are also correct in that you need to know which is which to test it. Same as before, from a fully open to a fully closed circuit between the "sender" terminal on the gauge, and ground, will give a full swing of the needle on a good gauge. In a working system the resistance varies in the sender as oil pressure changes, and that resistance is used by the gauge to give you a reading.

Thanks TV! But how do we know the gauge is toast before we determine if the wire is good or not? I was hoping to bench test the gauge but the CIH schematics do not ID the posts.

Sometimes you can read a wire # at the sender and then read it at the dash cluster plug.You may have to peel back some of the loom.You would have to probably pull the cluster and turn it over for access.A schematic is better tho.If you can id the wire in the plug,you might be able to trace it thru the cluster,whether it is a printed circuit,or wires.At the plug,look for terminals that are,OR,can be pushed back from the terminal side.That could be an open connection.Also if it is printed circuit,you might find loose solder connections.And like the TV said,mice might be chewing on your wiring,and that might be anywhere.
As you also said,at the gauge make sure you have 12v,and good ground.Here you need a multimeter.Check with key on and the gauge disconnected.The third wire/terminal should be from the sender,which as someone else posted,varies its resistance to ground thru the sender,which makes the needle move.That terminal should be open until you ground it at the sender,then have continuity to ground.You would need to prove out continuity thru the cluster from where the dash plug is.In other words say you do not get good readings at the gauge,check at the plug.It is very possible that the gauge is bad by your description,but senders and wiring fail way more often than gauges.I just hate to buy parts when the wiring is at fault:I don't like to guess or assume.I have figured out dash problems like this before without schematics so it is doable.Good luck,keep posting results,Mark.

Thanks for the good info! I'll reply to you and Bob at the same time. So today I returned to the farm with a full spool of wire and a good flashlight. I inspected the wire coming out of the loom that connects to the sender. A full inch of insulation was missing about half way between loom and sender. I cut the wire here and then attached it to my full spool with a wire nut. I unrolled the spool as I made my way up into the cab. Inside the cab I located the correct color wire (per the schematic) going into the plug for the gauge unit. Using a multi meter I checked continuity between the plug and the wire spool...the meter pegged over. Having satisfied myself that the wire was intact between sender and plug, I then checked all the OTHER wires in the plug to make sure there was no shorting between wires in the loom and there was not. So I turned off the key and plugged the gauges back in. Then I turned the key back on. At this point the oil gauge returned to zero...something it had not done in the past. When I took the end off the wire spool and touched it to ground it pegged over in the other direction...so the gauge would appear to be working. I then reinstalled everything and hooked up the sender and fired up the engine. The oil gauge has a very small "red zone" at the far left and dial markings that approximate 25%, 50% and 70-75% (2 marks)(100% would be all the way right). At an idle the gauge read around 25%. At full throttle it was half way between 50% and 70%...so around 60%. There is nothing on the gauge to tell you what the marks mean, but it is fully out of the red zone. When the engine was shut down, the gauge worked its way back to a spot that is just below the 25% mark and stayed there until the key was turned off and back on again...at which point it returned to zero. I am a little concerned either sender or gauge may be starting to go bad because the gauge needle did not move smoothly...it was a bit jumpy. Wondering what you think on that.

I then tested the oil warning lamp and it worked fine. I need to reinstall the sender for this in the block and have ordered a new "T" and adapter.

Gauge has been locked over one way- since it works at all it may free up. I would just keep an eye on it. It's a good idea to make sure it zeros out every time before you start it. On anything I have with an oil pressure gauge I'm looking at it at start up.

When you get the oil light sender plumbed in,then check it to come on before it starts.Get the engine up to operating temp and observe your oil psi at full throttle.Idle down,and when you shut down see that the light comes on as the engine dies.Tonight you may have had cold oil keeping the psi reading up a bit.You must have had an open in the bare wire end at the sender.Check it for continuity for fun.Any way-good job getting it to work! Mark

I was thinking that too. I think that bare wire shorted and pegged the thing over enough times that it stuck there. I manually freed it up with my finger while I had everything apart. That is when it started working. With the short repaired, I think the gauge will start working more smoothly as long as it is getting a clear signal from the sending unit. Sure do appreciate all your help! I'll be working on the oil light and hydraulic lockout late in the week.

Thanks! I'll be working on the right side of the engine come Saturday. As it turns out, the PO was picking sunflowers one year and the hydraulic lockout switch went bad so he could not raise and lower the head or unload. He called our favorite service guy and was told how to bypass everything (it was Saturday). He swears they put it all back together BUT what I ended up with was a plug in the block, a sender/switch/and "T" all hanging in space from wires. The adapter that goes into the block went AWOL and the male part of the "T" was broken off. Effectively, he circumvented every possible warning for low oil. I haven't mentioned it to him, and see no point in doing so, but this makes him partially responsible for the many thousand dollar repair bill I just paid. Ultimately though, I was the operator and I guess I was responsible.

So the new "T" and adapter will be in Wednesday afternoon. Thursday I work my regular job. Friday I have no help. So Saturday we are back in the game. Thanks much for the help, we will see you then!

Well the only way i know of it to R&R the gauge unit . I am not and expert on I H combines as for a long time around here nobody had one mostly Deeres if the had one or a Gleaner . As for me i had Massey's and loved them sold a few other Masseys to a few guys and they loved them. Now one of my close friends has a 1620 and we are learning .and another has a 6620 and boy is he LEARNING. He tolld me the last time i was down that if he starts getting his oil money again he and i are going shopping as he learned his lesson about not taking someone with him to look things over first. He said jokingly that each time i come down his check book gets lighter and i keep finding things.