Cat 12F electrical question

[Onfoot]

Appreciating already the collective wisdom and experience that resides in this forum! Especially given my newbie status.

As noted in a previous post, I am a newbie with a 1968 (maybe 1967 according to S/N, 59H498) 12F grader, affectionately known as Hanna. Starting was not a problem until I (foolishly, I now know) followed the instructions on the plate in the cab--leaving Heat on for a full two minutes before trying to crank. When I then went to crank, nothing happened. This led to all kinds of sleuthing--determining that the batteries were fully charged, that no fuses had blown and that the manual breaker switch had not tripped.

If I turned the master power switch off for a bit, then turned it back on, turning the start switch to Heat would produce some rattling in the solenoid relay. I replaced the solenoid relay thinking it might be the problem. But no go. (See attached photos to see all that I am referencing.)

I have wondered about the breaker switch, but if I bridge the two leads, it makes no difference.

However, if I connect the hot lead on the start switch directly to the positive battery terminal, everything works fine--the glow plugs glow (at least enough of them to start the engine--I think one or two might need replacing) and the starter works fine. And, once the old girl is running, I can disconnect the lead between the battery and the start switch and everything seems to be working fine. (Until I need to start her again--whereupon I pull out the alligator clips.)

Does anyone have any ideas about what I should test and how such testing might be done? Electrical is not my strong suite!
Thanks, guys! I am really wanting to get Hanna restored to her former glory.

 

[Coaldust]

Hmmm,

I’m reading that you can get Hanna to crank by bypassing the start switch? And by using the switch in the crank position, you only hear the starter solenoid clicking?

I would approach that as a faulty switch. If I was clocked in on that job, my next step would be to perform a quick voltage drop test across the b+ to S terminals on that switch.

Good chance that switch is older than me, and I’m pretty old. Maybe get a new switch?

Keep us in the loop with your adventures with Hanna! She is a helluva rig, old Hanna. Nothing can slow Hanna down.

She has six in the hole, and that girl can pull! Tell you what,....

Hanna has Caterpillar Power!
Rolling coal by the hour!

 

[Delmer]

There's a couple ways to go about this. Do you have a multi meter? and do you know how to measure DC voltage and ohms? if not, get one and watch some videos that explain it. If you don't mind spending a little money to save some hassle, get a powerprobe and learn how to use that. A powerprobe won't do anything you can't do with a multimeter and test leads, but it's easier to set up and some people swear by them.

The other thing you could try, especially if you still get the chattering noise, go through the wiring harness in the areas that should feed power to the solenoid, and see if you can wiggle wires or tap components and get the chattering to stop, or increase, or even get it to crank.

A wiring diagram could help, but that wiring is so simple you should be able to figure it out by following wires, and that process will help you understand what the system should do, and what could be broken to make it do what it is doing.

 

[Onfoot]

Hmmm,

I’m reading that you can get Hanna to crank by bypassing the start switch? And by using the switch in the crank position, you only hear the starter solenoid clicking?

Thanks, Coal Dust. I didn't explain it clearly enough. The switch works fine. And the solenoid in question is not the starter solenoid. You can see it in the photo attached. It is also called a start aid relay, to help with cold starts. (PN DR-1481 24c)

If I connect the battery directly to the hot wire on the starting switch, the switch works perfectly to heat the glow plugs and then to turn the starter motor.

 

[Delmer]

Sounds like your start switch is not getting power, which is why he suggested testing the voltage drop from the battery to the start switch. You know it worked, and then it didn't, we can guess that the high amp draw of the glow plugs/start aid caused a bad connection where the power supply for the glow plugs branches off from the power supply for the ignition switch. That's what you want to test with a voltmeter/powerprobe, and then follow the wires back from the ignition switch to the battery and the start aid relay big wire to the battery, those will connect at some point, and that is the first place I'd look. A volt meter will TELL you where the voltage is and isn't, otherwise you're guessing and could easily make things worse.

Edit: I would test for voltage at the B+ terminal on the switch and work back toward the battery.

 

[Onfoot]

Thanks, Delmer. I do have a multi-meter. No problem measuring voltage. (I live off-grid and have done all my own electrical work.) Ohms are a new skill, but I'm watching YouTube for testing the glowplugs in due course.

And I do have a wiring diagram--though the start relay does not appear. I wonder if it may only have been put in machines destined for cold climates. But the wiring is not hugely complicated---just all wrapped up. I'll post how I make out over the next few days.

 

[Coaldust]

Delmer is on the right track. Do what he suggested. You’ll eventually locate a bad connection.

Gotta get Hanna back in the game!!. If those wheels ain’t spinning, we ain’t winning.

 

[Bluox]

The item you replaced is a magnetic switch or a relay, the only solenoid you have is on your starter.
Your start switch triggers your glow plug relay.
You have a bad connection in the power wire going to your start switch.
If you want to buy a tool that will really help you buy a 50 volt test lite that has a digital voltage screen in it ,I keep mine under the seat in my service truck and solve 90% or more of electric problems .
good luck
Bob

 

[Delmer]

Good, you'll figure it out. Don't be fooled if you have voltage at the switch or anywhere else with nothing turned on, turn on the glow plugs and turn the key to start, a bad connection will give you a voltage reading with no load, and then no voltage with a load applied.

 

[grandpa]

Online, for your future, that solenoid on top of the starter will give you grief. We lucky buggers that live in extremely cold weather will have this problem. When you start your grader in severe cold it takes so much amperage to turn the engine it will fry the contact plate in the solenoid. Symptoms will be sluggish starter power or the starter may actually stay engaged after you release the start lever (plate welded itself to the contact studs). Good thing about your vintage is you can go in turn the plate over and run on a new side.

 

[Onfoot]

The item you replaced is a magnetic switch or a relay, the only solenoid you have is on your starter.
Your start switch triggers your glow plug relay.
You have a bad connection in the power wire going to your start switch.
If you want to buy a tool that will really help you buy a 50 volt test lite that has a digital voltage screen in it ,I keep mine under the seat in my service truck and solve 90% or more of electric problems .
good luck
Bob

Thanks, Bob. It is called a 'cold start relay' in some of the Cat literature. So thank you for the correction. And it clearly was not the issue. I have a PowerProbe on its way which I hope will speed up the wire continuity testing. I spent a couple of hours looking for issues today, trying to follow wiring harnesses and test things with my multimeter as best I could. I found nothing that was out of order, so far as I could tell. I did make a schematic of the wiring as it is behind the instrument panel, which I have attached. By rights, the issue, as you note, must be in the red wire somewhere south of the manual breaker, given that there is no power coming to the breaker. And there is power showing at the starter solenoid, where the red wire is supposed to connect. But I certainly value your thoughts! (I note, for example, that the voltage on the solenoid was showing 23V and the battery was showing 25V. Should there be that much of a drop?)

 

[Bluox]

I would start by cleaning the connection at the starter switch terminal where the battery cable is connected .
work your way back to the battery cleaning connections .
Your power switch should be a battery negative cable disconnect to ground.
At this point what do you have power to?
The power probe may not be the best tool in this case ,I've seen a lot of damage done with them and a lot of bad guesses of problems .
Like I recommended a test lite with a voltage reader in it is about 1/5 the price and works well finding opens and bad connections.
Good luck and hang in there
Bob

 

[Onfoot]

I would start by cleaning the connection at the starter switch terminal where the battery cable is connected .
work your way back to the battery cleaning connections .

This afternoon I cleaned the connections on the solenoid where the + battery lead and the red lead from the start switch connect. I have full battery voltage to the terminal. By rights, there should therefore be power at the breaker terminal (#3 in the diagram I provided). There is not. So there has to be a discontinuity between the solenoid and the breaker switch. Tomorrow I will run a lead between them and see what happens. Stay tuned!

 

[Coaldust]

Appreciate the update. The pressure is on to get Hanna running. Keep up the good work.

 

[Bluox]

This afternoon I cleaned the connections on the solenoid where the + battery lead and the red lead from the start switch connect. I have full battery voltage to the terminal. By rights, there should therefore be power at the breaker terminal (#3 in the diagram I provided). There is not. So there has to be a discontinuity between the solenoid and the breaker switch. Tomorrow I will run a lead between them and see what happens. Stay tuned!

Look to see if that red wire on the starter goes to the ammeter then to the circuit breaker?
Bob

 

[Onfoot]

Look to see if that red wire on the starter goes to the ammeter then to the circuit breaker?
Bob[/QUOTE

As per the schematic I posted, the red wire runs from the solenoid to the breaker to the ampmeter to the switch. There is power at the solenoid, but no power at the breaker switch. Kind of narrows down the possibilities, I think...

 

[Delmer]

No, there should not be that much drop unless the starter is cranking. If you have 23 volts (and that's probably with nothing on, right? ) then you turn on the glow plugs or starter solenoid or whatever, and that resistance lets very little current flow causing the voltage to drop to an unusable level. Double check voltages under load. Intermittent poor connections make simple problems complicated. You have a simple problem, IF you look at it right.

 

[Onfoot]

Hi guys. Thank you again for all the tips and wisdom. The good news is that Hanna is back in business! After much sleuthing and terminal cleaning, etc., I discovered the issue--the hot wire running from the solenoid to the start switch was broken and shorting out in the metal tube that transported the wiring harness from the front of the engine compartment to the rear, with holes for various leads to come out. (Sparks and smoke coming out of the harness tube was a dead give-away!)

To make life more interesting, the metal tube made contact with the temperature indicator capillary tube, melting it. And of course I did not know what damage had been done to the wiring harness within the metal tube. It was packed solid with 53 years worth of crud, so there was nothing to do but cut all the wires, remove the tube, and rebuild the wiring harness. So that is what I did. Fortunately, the leads coming off of the pin connector were in good shape. So I was able to splice equivalent gauge wiring to the pin connector and effectively rebuild the harness. (All my splices are soldered and then sealed with heat shrink wrap.)

So all is now working with the electrical system. Hanna started fine, though I am not convinced that all the glow plugs are glowing. But that's for another day.

Thanks again to all!!!

Oh yeah...I was able to replace the temperature sensor as well--though I ended up paying Caterpillar one arm and part of a leg for it...

 

[DB2]

Just to say I recently got one of the voltage displaying test lights that Bluox described and now I can not believe how I made out without one.

Definitely worth the investment.

 

[Onfoot]

In the way of an update, gave Hanna a good workout tending to my 2km gravel driveway--pushing back snow banks so I could widen the cleared path. Took a couple of runs each way, with some fancy work cleaning up at each end. She did well. Started up on the first try this morning (about -5C) and ran without a hiccup--though I did break the shear pin about half way through. I'm learning that some mouldboard movements should not be done under load. (I was turning the circle with a heavy oad of snow.) It only took a moment to replace the shear pin, but then I could not get her to start. Turned over fine and all, but no ignition.

So I called the previous owner--a great old fellow, now 82 years old who has only ever driven graders for a living, having started when he was 15 years old. I explained my issue and he, naturally, immediately asked if I had turned the fuel cutoff switch back on. Of course I had not. To turn off the engine, you have to pull out the accelerator pedal. And, if you don't push it back in, the machine will not start. Talk about feeling rather stupid... I have lots (and lots!) to learn!