Ford 1920 alternator output

[jinman]

Bob, I don't think I'd go that high. If it were 8 amps, I might go to 10, but a 5 amp jump is a lot. Blowing a 10 amp fuse is a significant short, indicating something definitely wrong instead of a slightly increased current draw.

DieselMonk, with the tractor running I was getting 12.2v at the battery and at the alternator. With all lights on it dropped to 11.95 at both. That's what made me think the alternator might be bad. If the alternator was bad, wouldn't that only be evident with the tractor running?

Bob

Were these readings with the fuse blown? If so, your alternator had no voltage reference to the regulator and that's why you were not getting 14 volts. Since the fuse stops blowing when you disconnect the inst pnl, I would spend most of the time troubleshooting that.

 

[Spicer]

DieselMonk, with the tractor running I was getting 12.2v at the battery and at the alternator. With all lights on it dropped to 11.95 at both. That's what made me think the alternator might be bad. If the alternator was bad, wouldn't that only be evident with the tractor running?

Bob

You are only getting 12.2V at the alternator because when you blow the fuse on Jim's blue highlighted wire there is no power for the voltage regulator or field windings.

Mike

 

[MA1920]

To all those that helped, with special recognition to Jim, I found out why the fuse was blowing. I mixed up two wires on the instrument harness.:banghead: After studying the wiring diagrams, I was able to figure out which wires I put on the wrong terminals. With the tractor running I now get 14.13v at the battery.

But, the glow plug warning lamp stays on longer than the 4 seconds that the manual states it should stay on. Is it safe to say the timer may be bad? The service manual says that "if the timer relay malfunctions it will adversly affect the indicator lamp, however the glow plugs will continue to function properly."

The new harness has two less wires than the original. After following the wire diagram, they are the "Reserve Tank Sender Unit" for the coolant overflow, and the "Parking Brake Switch". I would like the parking brake indicator to work, because more than once I started to drive with the brake on. But wiring that to the instrument panel might be more hassle than it's worth. I wonder why New Holland thought those circuits weren't important?

Once again, I'm somewhat embarrassed, but I did learn something about trouble shooting and reading wiring diagrams, so Jim, don't feel like you wasted your time. I really appreciate your help.

Bob

 

[MA1920]

Update part 2: I cannibalized the old harness and removed the two wires I needed for the Reserve Tank and Parking Brake circuits. All that's left to get it to pre-mice condition is to verify the glow plug timer.

Bob

 

[jinman]

Bob, you should not feel like you wasted my time at all. You did exactly what I wanted you to do by getting away from the glow plugs and troubleshooting wiring problems. All I can do is offer you a big :thumbsup: for taking the time to do some tedious checking.

I think your glow plug timer's running a bit longer is fine. Is the glow plug lamp anything other than a normal light? I think the note means that the timer just runs the light. If the timer fails, glow plugs will still work. That's a point I was making all along. I would not worry about that extended time for a second. If your light stays on after you go out of preheat or the lamp quits going on, you probably need to replace the timer. New Holland wants over $65 for the timer, but you can buy them on eBay for around $12 or $13 including shipping. It's a S81NL. On my tractor, the timer actually controls the glow plugs, but yours just runs the light. I sure wouldn't replace it because it was off by a couple of seconds.