Ford 1920 has power, but won’t crank

[AlpineSki]

Weird situation here. I’ve had this happen on a 1984 chevy truck, my sons 1998 Volvo, and now my 1996 Ford 1920 diesel tractor. Battery new. Alternator and stater checked and good. New ignition switch and harness, new dash, and new (good used) wiring harness. Turn the key and the fuel shut off valve clicks, as it always has. Gauges come alive (fuel needle begins to rise), have lights, etc. turn the key farther to crank, everything dies. No power. Gauges flat, no click, nothing. Only way to get it back is to disconnect ground at battery. Then I get power like before, but same thing happens. Ground strap is good and I cleaned all ground connections. Haven’t solved the problem with the chevy, but with the Volvo it would do the same thing, but then although the battery was showing 12.5 volts, it still wouldn’t start. As soon as you try, everything dies. No dim interior lights, etc. Decided to hook up a battery charger and as soon as I hit on, lights came back, then it started. Didn’t work for the tractor. I’ve asked countless auto people including a local auto electrician guy I used for everything. No clue. Please help. I’m desperate to get this tractor going. Any thoughts greatly appreciated. Thanks, J

 

[Roadworthy]

The Chevy and Volvo only muddy the water and have no bearing on the tractor problem. Try putting the voltmeter on the battery. If all is well you should see your 12.6 volts from the fully charged battery. While monitoring the voltage note what it is when you turn the key on and again when you move it to start. Then see what the battery reads after the start is attempted. This may give us a starting point.

 

[AlpineSki]

12.56 at the battery. Virtually the same thing at the starter (positive cable goes to the starter directly). Turn the key 12.56 remains. Try to start, everything dies, battery is all over the place. Drops significantly. Remove cables and test battery, 12.56 volts.

 

[Fuddyduddy1952]

Looking at diagram it has a neutral safety switch and relay. I'd check that making sure ignition switch is wired properly (crank position). Something isn't allowing starter solenoid getting power. You could jumper power to solenoid temporarily to be sure it cranks or check voltage there (switch in crank position) working backwards. Number 7 on diagram shows a fuseable link off of starter.

 

[ROUSTABOUT]

Could be a bad crimp on a main bat cable somewhere. It will carry a little voltage but give out when demands a lot of voltage. Seen folks spend a lot of money, and that was the problem the whole time. Seen it numerous times. It's the first thing I check.

 

[AlpineSki]

Would that cause there to be no power then to the system? It’s like a breaker is getting thrown and the only way to reset is to disconnect the ground, wait a little bit, then reconnect. I’ll check the main positive cable going from the battery to the starter.

 

[AlpineSki]

Looking at diagram it has a neutral safety switch and relay. I'd check that making sure ignition switch is wired properly (crank position). Something isn't allowing starter solenoid getting power. You could jumper power to solenoid temporarily to be sure it cranks or check voltage there (switch in crank position) working backwards. Number 7 on diagram shows a fuseable link off of starter.
View attachment 801186

The neutral safety switch is new (good used).

 

[AlpineSki]

I just tested the cable going from the positive battery terminal to the starter and I get zero resistance. So the cable is good.

 

[Harry in Ky]

I just tested the cable going from the positive battery terminal to the starter and I get zero resistance. So the cable is good.

No, not really. It means the cable offers no resistance to your ohm meter. That's all it means.

Since you have a volt meter and know how to read it, you might try this. Go to the starter and locate the signal wire from the start circuit. Usually a single wire with a spade terminal. Find that and remove it. find a suitable jumper wire to connect the spade on the starter to battery positive. Key, lights, gauges, all that turned off, transmission in neutral, and all that. Place your voltmeter negative lead to a ground on the frame (not on the battery post) with the positive lead on the starter battery cable stud. Now apply the jumper wire to the starter spade terminal for a second or two. What happens? Both with the starter, and also with the meter?

If the starter engages the engine cranks over and the meter holds at 8 to 10 volts while doing so, then the starter, battery, and both cables are probably good. On the other hand, if it repeats the results you've gotten so far with all your other tests, then one of the four is letting you down. It's probably not the starter.