Main Fuse Blown and Fuse Block Melted - Help!

[bartonkj]

New Holland TC29DA. The 40 amp main fuse blew and melted the fuse block. Slot B of the ignition connector (12V Input terminal) also melted. The wire and wire coating are OK, but the plastic surrounding that particular wire melted. I tested the ignition switch and it passed all of the tests in the repair manual. A few months ago, the dealer replaced the starter, the battery, the water pump and a few other things, but I have put less than 10 hours on it (over 2 - 4 days of use a week or two ago) since the repairs. I can't afford the time or the money to have the dealer repair this again.*

Behavior before fuse blew:
I started the tractor last night and when I held the key in the glow plug position, the glow plug did not go out after the normal interval. I held it for several seconds to see if it would go out. It did not. I then started the tractor and the glow plug light went out and the tractor ran fine. I took a load of heavy trash to the end of the drive, set the parking brake and set the gear selector in neutral (the PTO was not engaged). The tractor was running fine as I was unloading the trash. I had the high beams on and I had the hazards on. Then it just died, but it wasn't just the engine that died: all the lights died too (I know, consistent with the main fuse blowing).

Questions:
A) Any ideas on what might have caused the fuse to blow, or what I should check next?
B) I assume I will have to splice in a 40 amp fuse block into the wiring harness? Please correct me if I'm wrong (the wires go into the harness and I can't tell where they go from there - I mean I think the wiring diagram shows 1 end going to a junction with the battery, the starter solenoid, and the alternator, but I don't have experience with wiring diagrams and looking at a diagram is very different from looking at the physical wires. Also the wires into the fuse block are very large, but I don't see other large wires). Where can I get a replacement fuse block?
C) Where can I get a replacement connector for the ignition switch?


*1) It is blocking my driveway, 2) The front end loader is in the down position, so I don't even know how they would load it on the truck, and 3) We are in the process of moving which makes for all sorts of other complications

 

[WinterDeere]

No answers here on anything specific to NH or your tractor, but as far as blowing the fuse and melting, some basic theory:

Fuses operate on temperature, not current. They're rated for current, which yields a predictable temperature when all connections are clean and tight, but they're temperature-yield devices. Meaning that, if you have a loose or corroded connection close to the fuse, it might yield sufficient heat to blow the fuse even when current is below specified fusing current.

I say that because you mention the fuse block itself melting, which makes me suspect a bad contact somewhere in there, either between wiring and fuse block, or fuse block and fuse itself. Heat generated will eventually blow the fuse, but perhaps was not coming from fuse itself, and instead from a bad contact point.

The connector with the single melted contact could be the result of a contact that was not properly "latched in" to the connector housing during assembly. In that case, rather than properly capturing the mating pin, the contact could have backed out of the housing when mated. In that case, it's still likely touching the pin, but not in any way sufficient to carry the specified current. The result is higher resistance, and as a result of P = I^2*R, higher power dissipation and temperature rise at that contact.

If it were me, I'd buy a new connector housing from NH, figure out how to extract those contacts from the old melted housing, and install into a new connector housing. There should be plenty of videos on youtube for how to do this, if you don't already know, but the contacts are generally crimped onto the wire before sliding into the housing, and small fish hook type barbs on each contact hold them into the housing. They can usually be released and extracted with dental tool or thin knife blade (e.g. X-Acto).

Temperature rise in any terminal or wiring follows P = I^2*R, so if temperature is high, you really only need to check current to determine the cause. If current is above spec, there you have it. If current is at expected level, then start hunting for R.

 

[WranglerX]

Basically it does not look like a "fuse block" looks like a male/female Weather-Pac connection.....

 

[nyone]

Bussman makes good fuse holders. I would not use a cheap off brand.

Bad connections can cause this to happen.

 

[bartonkj]

So an amazingly fortuitous thing happened. As noted in my original post, my tractor broke down at the end of my driveway. I was working on it yesterday evening to replace the 40 amp main fuse holder with an inline 40 amp resettable breaker switch. A man (Tom) who just retired as a mechanic from a local tractor dealer, was driving by and stopped. He asked what happened and I explained. He said he couldn't do anything then, but could come back tomorrow. I happily accepted. I finished installing the inline breaker last night. Although one of the fours wires in the connection for the ignition switch got too warm and melted a little of he plastic, I deemed it still OK to reuse for now. I reassembled that, then turned the ignition to the glow plug heat position and the glow plug light went off at the proper time instead of staying on. I didn't try to start the tractor then.

Today, Tom came over and we went over the tractor together looking for any frayed wires or shorts. As best as we can tell, here is what happened. Oddly enough, even though the 40 amp main fuse was melted and the fuse connector was melted, the fuse never blew. Once Tom cleaned off the fuse blades enough to get a connection, he tested and there was continuity (this as not the first thing we did, btw, he had a thought after we talked quite a bit about what happened and what might have caused it). The starter had been going bad for a long time. It would only start intermittently, so I had to turn the ignition multiple times until it would finally catch. Tom suspected the bad starter cause a lot of heat to build up in the main fuse over time and it melted, but didn't draw enough amps to pop. There was still enough of an electrical connection to run the tractor until for whatever reason the night it broke down it finally had enough and the circuit was open due to corrosion on the burnt components rather than popping the fuse.

At the same time, there appears to be a problem somewhere with the hazard lights. When the engine is not running, the hazard lights work fine and the turn signals work fine. HOWEVER, when the engine is running and the hazard lights are on, they start flickering and don't work correctly. The problem is even worse when the headlights are on, too. We don't know what exactly is causing the problem, but I was satisfied with the situation for now. I just won't use the hazard lights (I can get by without) for the time being.

 

[nyone]

Does this unit have the starter relay mod done?

 

[bartonkj]

No. Can you tell me more about that?

 

[nyone]

Your basicly putting a relay in the trigger circuit of the starter. It takes away alot of the load on that circuit. I would search for the starter relay mod.

I believe these NH machines are known for burning up fuses and the plug on the key switch.

 

[thclimer]

Starter circuit modification (long read with good links):

TC33D wont start

Ignition switch replacement:

TC33D Glow Plug Problem Fixed

 

[bartonkj]

Thank you.