Electrical gremlin in a 314-H

[HankB 16]

I'm just starting on this and it looks weird.

My lights weren't working. Also the hour meter and voltmeter weren't working. Neither was the seat switch PTO interlock. I finally got around to checking the lights and found that the one bulb was still good. The other bulb had broken and all that remained was the dangling wires. (I don't recall how that happened, but I put a new bulb in) I checked fuses and found the 15A one blown. I replaced it and now had two working headlights, along with a working hour and volt meters. Even the seat switch interlock now worked. This was like magic!

A couple days later I noticed that the fuse was blown again. I suspected a problem in the lighting circuit since that wiring goes the furthest in the tractor. It also took out the Volt and hour meter along with the interlocks. I replaced the fuse again and left the lights off. It blew again so I can rule out problems from the light switch to the lights.

Today with temps nearing 30° I decided to spend some time troubleshooting it. I started my measuring resistance from the load side of the (blown) fuse to ground and got open (e.g. no continuity as indicated by my Fluke DMM.) I switched the light switch to on and got about 60 ohms to ground (IIRC - I didn't pay much attention as long as I saw the mater change from open to something when I flipped the switch.)

I left the light switch off and held the meter in place while I grabbed and wiggled every wire I could see. I was hoping to find a short by moving things around, but could find nothing.

Then at one point I connected the meter (again to the load side of the blown fuse) and saw about 160 ohms. I flipped the light switch on and saw it drop to 0 ohms.) As I sit here and ponder this, I'm realizing that a 55 watt bulb must draw a bit over 4A to consume 55W and that means at 12V, it would need a resistance of about 3 ohms to do this and I also realize that a cold bulb will have a lower resistance until it heats up. So put two 55W bulbs and the tail lights in parallel and they will read pretty close to 0. Doh! I thought I'd found something.

The other interesting thing is that the resistance continued to drop. At the latest reading, it was about 95 ohms. I guess that other resistance is from the hour meter and volt meter.

The other thing that I wondered about was the LED indicator module in the dash. These wires run to that as well. I unplugged it and find that the headlights work without it and the tractor can start and run. I'm going to leave it unplugged to see if that makes a difference. Has anyone found that these go bad in a way that results in blown fuses? (Actually, in the wiring diagram I'm looking at - page 7-54 of the Demystification Guide - it looks like the lights should not work with the LED module unplugged or the parking brake on, but they certainly do.)

Any other common trouble spots in the wiring that I should be examining for a possible intermittent short in that circuit?

I'll also add that we purchased this tractor new so I know the wiring is as it was from the dealer. maybe when the weather warms, I'll pull the dash and battery and trace wires to see what's really there.

Any suggestions are appreciated.

[rmaynard 14,951]

Just a guess, but if the circuitry finds it's way through the ignition switch, you may have a problem inside it. For example, if moisture is shorting between the accessory contact and the coil contact, that will draw pretty heavy amps.

Bob

[HankB 16]

Just a guess, but if the circuitry finds it's way through the ignition switch, you may have a problem inside it. For example, if moisture is shorting between the accessory contact and the coil contact, that will draw pretty heavy amps.

Bob

Hi Bob,

Thanks for the tip.

It's hard to say. According to the wiring diagram the ignition switch is protected by the 25A fuse and the 15A fuse is between the ignition switch and ground. In other words, there should be no way the ignition switch can short and blow the 15A fuse. But I also note that the seat/PTO interlock also should not be disabled by pulling the fuse and I know it is. So it might be something to look at.

thanks,

hank

[rmaynard 14,951]

Without a diagram in front of me, everything is a guess. Good luck. I hope you find the problem.

Bob

[Bow_Extreme 538]

Does this tractor have the fuse block next to the battery? It's a 3 place or 4 place fuse block?

[DoctorHfuhruhurr 136]

I kept blowing fuses sporadically and wasn't able to easily locate the issue so I just replaced the fuse with a 12v breaker type fuse that can be reset with the press of a button. I got it on ebay for $5 ish. It's not the best solution but it's a handy work around until you find it.

[HankB 16]

Does this tractor have the fuse block next to the battery? It's a 3 place or 4 place fuse block?

IIRC it's a 3 place fuse block with two fuses. I'll get a picture of that tomorrow.

I kept blowing fuses sporadically and wasn't able to easily locate the issue so I just replaced the fuse with a 12v breaker type fuse that can be reset with the press of a button. I got it on ebay for $5 ish. It's not the best solution but it's a handy work around until you find it.

Sounds like that might be handy.

thanks,

hank

[Bow_Extreme 538]

Replace the fuse block!! That is an open top fuse block. All the elements get inside the fuse holders and arc the fuses from one terminal to the next. This is most likely your problem. The best solution I found so far to deal with this is single sealed automotive fuses. Buy 3 of these and solder and shrink wrap them in. I removed the bracket the fuse holder is mounted to and mounted the fuse terminals next to each other on the inside wall of the upright. If I can find some pics I will show them to you.

Be careful when doing this. Two of those fuses are jumped together on one side so they essentially require the same source of 12V power. This will probably take a couple hours to repair but will permanently repair the electrical problem.

[HankB 16]

Oops - I forgot that I promised a picture today.

Replace the fuse block!! That is an open top fuse block. All the elements get inside the fuse holders and arc the fuses from one terminal to the next. This is most likely your problem.

Yes, it's wide open and right next to the battery. Seems like a recipe for trouble. I'm heading to the auto parts store for some other stuff so I'll pick up a couple fuse holders and decent selection of shrink wrap.

Thanks,

hank

[W9JAB 156]

:thumbs:

fuse block looks pretty ruff, My plan

is to jump out the fuse and watch for

the smoke :banghead:

[Bow_Extreme 538]

Hank,

Here are the pics of what I did:

#1 - Inside

#2 - Outside bolt locations

Good Luck

[rickv1957 70]

Too much electrical on the newer models,Rick

[Bow_Extreme 538]

Come on Rick. It's honestly not that bad to work with. Imagine a completely automated machine with dual robots, multiple stations, molding machines, and one computer, PLC software, and many cabinets full of electronics to help integrate the machine into one smooth operation. Now that can be a headache at times but it makes tractor wiring look like baby steps. But it's all fun no matter how frustrating it can be at times. :thumbs:

[HankB 16]

With the temps above freezing yesterday, I finally got around to replacing the fuse block with two in-line fuses. No joy. After starting and running the tractor, I found the 15A fuse blown. Next I installed the 20A breaker in its place and on the following start, the engine started to crank and then stopped. I found the 25A fuse blown which is a first. Even when I replaced the 15A fuse with a 30A fuse (because I had burned through my supply of 15A fuses), the 30A fuse blew. Maybe the breaker has a different time characteristic. I know that in some electrical distribution systems fuses are used where the fastest response is required because they can open faster than a breaker. (As an aside, you can see one blow here:

- I did some work for a company that designed and made stuff like that.)

So I'm a bit bewildered. But I'm also going to take a hard look at the starting circuit since I was cranking when I blew the last fuse.

I also had the LED indicator board disconnected during this so I can rule that out as the problem.

I might just wait for spring or summer to deal with this. The tractor runs fine w/out the 15A fuse. I just lose indicator LEDs, headlights and safety interlocks.

[pfrederi 17,197]

My C-175 just went through several fuses. The headlights would work fine in the shop but after plowing for a bit they would be dead. Replace fuse all was well ...in the shop..plow for a bit fuse blown. Checked wires with multimeter no short

Finally on a warmer day got down on the ground and followed head light wire...there was a bare spot that got hit by the front steering plate only on tight left turns.....

[WheelHorse_of_course 99]

Wire up a 12V light bulb to two male quick fit connectors and place this in place of the fuse that is blown.

This arrangement keeps you from melting thew wire harness since you have limited the maximum current to the rating for the bulb.

Now drive around and when the bulb come on stop and do the wire wiggling thing.

I have used this trick a number of times to troubleshoot all sorts of things including a telephone key system.

:thumbs: