Electrical probs

   / Electrical probs #1  

AlbionWood

Bronze Member
Joined
Nov 4, 2010
Messages
98
Location
Albion, CA
Tractor
Ford NH 1920
Backing up a little from my earlier query about the solenoid on the Ford NH 1920. This tractor was running fine, always started right up, except the neutral safety switch was kind of fussy - had to jiggle the shifter to get it to close. Shut down normally one day, next morning climb on and turn key - nothing! Check battery - 12.8V. Same at solenoid terminal - 12.8V across the terminals. Wait, the fusible link appears to have broken off... connect with new ring terminal, still won't start. Jump solenoid (hot terminal to spade connector) - nothing. OK, solenoid dead.

But wait, there's more... Checking the ignition switch, get screwy voltage readings. Hot lead in is at 12.8V, no problem. Turn to "Run" = about 7 V. ??? "Start" = less than 1V. Glow plugs = less than 1V. Not zero, mind you, but about 0.3V.

So - ignition switch bad too? Would this maybe have caused the solenoid to go bad, not getting a full 12V to turn the starter motor? What are the chances that the safety relay is bad, too, and is there any way to test that? (It's a four-blade relay, mounted above the starter motor, not quite sure exactly what it does really...)

(BTW, I tested all these after shorting across the neutral safety switch, so that isn't the problem. Took battery out and charged overnight just to be sure.)

Ford NH 1920, UP 31629 (mfr 1992), 4-cyl diesel
 
   / Electrical probs #2  
Backing up a little from my earlier query about the solenoid on the Ford NH 1920. This tractor was running fine, always started right up, except the neutral safety switch was kind of fussy - had to jiggle the shifter to get it to close. Shut down normally one day, next morning climb on and turn key - nothing! Check battery - 12.8V. Same at solenoid terminal - 12.8V across the terminals. Wait, the fusible link appears to have broken off... connect with new ring terminal, still won't start. Jump solenoid (hot terminal to spade connector) - nothing. OK, solenoid dead.

But wait, there's more... Checking the ignition switch, get screwy voltage readings. Hot lead in is at 12.8V, no problem. Turn to "Run" = about 7 V. ??? "Start" = less than 1V. Glow plugs = less than 1V. Not zero, mind you, but about 0.3V.

So - ignition switch bad too? Would this maybe have caused the solenoid to go bad, not getting a full 12V to turn the starter motor? What are the chances that the safety relay is bad, too, and is there any way to test that? (It's a four-blade relay, mounted above the starter motor, not quite sure exactly what it does really...)

(BTW, I tested all these after shorting across the neutral safety switch, so that isn't the problem. Took battery out and charged overnight just to be sure.)

Ford NH 1920, UP 31629 (mfr 1992), 4-cyl diesel

Your fusible link is toast. Replace it. Important indicator is low voltage at the battery terminal of the ignition switch when a load is applied. Cost of the key switch is immaterial; you don't need one.
 
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   / Electrical probs #3  
Backing up a little from my earlier query about the solenoid on the Ford NH 1920. This tractor was running fine, always started right up, except the neutral safety switch was kind of fussy - had to jiggle the shifter to get it to close. Shut down normally one day, next morning climb on and turn key - nothing! Check battery - 12.8V. Same at solenoid terminal - 12.8V across the terminals. Wait, the fusible link appears to have broken off... connect with new ring terminal, still won't start. Jump solenoid (hot terminal to spade connector) - nothing. OK, solenoid dead.

But wait, there's more... Checking the ignition switch, get screwy voltage readings. Hot lead in is at 12.8V, no problem. Turn to "Run" = about 7 V. ??? "Start" = less than 1V. Glow plugs = less than 1V. Not zero, mind you, but about 0.3V.

So - ignition switch bad too? Would this maybe have caused the solenoid to go bad, not getting a full 12V to turn the starter motor? What are the chances that the safety relay is bad, too, and is there any way to test that? (It's a four-blade relay, mounted above the starter motor, not quite sure exactly what it does really...)

(BTW, I tested all these after shorting across the neutral safety switch, so that isn't the problem. Took battery out and charged overnight just to be sure.)

Ford NH 1920, UP 31629 (mfr 1992), 4-cyl diesel

Ok wood, I see from your profile that you are a Farmer with little or no experience shooting electrical problems. The reason I say this is for a starting point. No need to see complex equations on how things work, better to explain in simple terms.

Now if you have a battery [12.8 v] and have a long wire connected to each terminal and you measure the voltage at the end of the wires, you will see the same 12.8 v. Why? Because no current is flowing and there is zero loss in each wire.

Lets connect a bulb at the ends of the same wire. You will measure the same 12.8 v at the battery terminals and 10.0 v at the bulb connections. Why? Because there is a current flowing now, each wire has a loss of 1.4 v.
Another way to look at it is, battery [12.8 v] = wire [1.4 v] + bulb [10.0 v] + wire [1.4 v].

Now, if we change the bulb to one that draws a larger current keeping everything else the same. The voltage at the bulb will be less [9.6 v] and the voltage loss for each wire will be 1.6 v.
Obviously, the resistance of the wire has a direct effect on the voltage across the bulb.

How do we apply this? Ideally there should be no voltage loss through a switch contact set, 12.8 v in = 12.8 v out.
In the real world you will see 12.8 v in and 12.6 v out, 0.2 v being the contact loss.
Seeing 12.8 v into the switch and 7 v out = 5.8 v loss.
Seeing 12.8 v in and 1 v out = 11.8 v loss in the switch.

The conclusion is that the internal switch contacts are bad, replace the switch.

Relays are more complex. What is inside the relay?

1] A coil of wire wound on an iron core and a armature to move a set of contacts and a return spring.

2] 3 three contacts points.

A] An Operating Contact or a Common Contact that is attached to the movable armature.

B] A Normally Open contact.

C] A Normally Closed contact.

D] Leds for connections.


You can measure the resistance of the coil, say 10 Ohms. Therefore the currant would be 12.8/ 10 = 1.28 amps.

The NC, Normally Closed contacts should be near zero resistance.

The NO, Normally Open contacts being open will have infinite resistance.

The only way to read the resistance of the NO contacts is to apply power to the relay coil which causes the NO contacts to close.
 
   / Electrical probs #4  
My guess is you have a bad ground or a bad positive conection. You have voltage, but no curent flow. But then again if your battery has a short it can cause similer problems, but not as acute, you would have battery voltage, with the key on, and very low voltage, or no voltage in start.
Dave
 
   / Electrical probs
  • Thread Starter
#5  
Your fusible link is toast. Replace it. Important indicator is low voltage at the battery terminal of the ignition switch when a load is applied. Cost of the key switch is immaterial; you don't need one.

What about the solenoid? The fusible link should have no effect when I jump the terminals, right?

I'm going into town tomorrow to get new fusible link, key switch, and maybe order a solenoid if we can sort that out. Will replace each of those in turn and see which makes the tractor start!
 
   / Electrical probs #6  
Had a similar problem with an old Massey 35 with a Perkins diesel.

Ended up being a corroded battery cable right inside the clamp where it connected to the battery post.

Cheap fix - maybe worth a look.

Bob
 
   / Electrical probs #7  
The best way to troubleshoot a starter circuit is with a Voltage Drop test. Use a digital DC voltmeter. You can get pretty good ones these days for $20.

Put one lead on each side of each connection and turn or have someone turn the starter key. Wherever you see a large voltage drop that is where your bad connection or component lies. There should be a small fraction of a volt dropped across each component EXCEPT the starter itself. Across the starter is where you should see the voltage.

Example of a test point. Put one lead on the positive battery cable and the other lead on the battery terminal. If it is a good connection you will get no more than a millivolt or two. Then put one lead on the battery terminal and the other lead at the other end of that cable and repeat the test. You should see a very small fraction of a volt as the key is turned. Just keep going down the line measuring across each connection and component until you find a significant voltage drop. When you find the voltage drop, there's your problem or at least one of them.

Don't forget to do the voltage drop test from the negative terminal of the battery to the engine block to test your ground connection.

Hope this helps.
 
   / Electrical probs #8  
Read post #2. Start there. A bad fusable link will cause all your problems. You cannot repair a fusable link, Replace it.
Bill
 
   / Electrical probs
  • Thread Starter
#9  
Replaced fusible link - no change.

Tested ignition switch for continuity - 0.5 ohm resistance across each closed circuit - switch seems OK then.

Tested battery cable leads by looking for voltage drops along the way - nothing, have 12.63V everywhere.

Pretty sure now it's the solenoid. I guess it and the fusible link went bad at the same time?

Good news: Found online sources for solenoids at < $50 (compared to $265 from NH dealer). Bad news: Have to wait days and days for shipping. Gonna miss the window for getting my covercrop seed in the ground. (Again.)
 
   / Electrical probs #10  
I had a problem like this about a month ago. The stud on the selenoid that the positive cable connects to was slightly loose. I took the cable off and tightened the inner nut and the problem was solved. Where were you able to find a selenoid?
Bill
 
 
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