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Electrical system

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#1 FarmKing74 OFFLINE  

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Posted November 16, 2016 - 04:27 PM

I am currently working on my restoration of my late father's mtd 990. I have followed the wiring diagram in the owners manual however I am not getting any current through the amp meter or the lights to show life. I am about to haul it to a small engine shop and pay to have it fixed but I would rather do it myself as I have the rest of the project, any help out there?

#2 crittersf1 OFFLINE  


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Posted November 16, 2016 - 05:15 PM


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#3 boyscout862 OFFLINE  

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Posted November 16, 2016 - 05:15 PM

Welcome to GTT. You have a heritage tractor and a good atitude. First, relax, you came to the right place. Second, download the manuals that you need from our Manuals Section. Let us know how experienced you are with electrical diagnosing and post a few clear pics of your wiring. Then we can talk you through what you want to know. It is not hard when you take it a step at a time. This as a great hobby but it can become an adiction. Good Luck, Rick

Edited by boyscout862, November 16, 2016 - 05:19 PM.

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#4 firefight100 OFFLINE  

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Posted November 16, 2016 - 05:24 PM

  schematic electrical.jpg

I have included the schematic.  

The lights come off a separate ac electrical side of the alternator, and do not go thru the ammeter.  

Also the dc charge circuit is only 3 amps, so you wont see much ammeter movement.

Hope this helps.  

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Posted November 16, 2016 - 05:58 PM

:iagree: , and :welcometogttalk:

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#6 grattone OFFLINE  

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Posted November 16, 2016 - 08:04 PM

First thing I would do is to find out if you are charging. As posted earlier you will not see much change with out a load on the system.

Would it be possible for you to put a voltmeter across the battery + to + and - to -  read the voltage? Then start the engine (rev it up to mid throttle) you should see a increase in voltage across the battery. You will need a load on the system to see a change on the amp meter, that would be the lights.


Hope this helps


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#7 VTXrider ONLINE  

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Posted November 17, 2016 - 07:16 AM

Welcome to the forum.


Pictures and the model number will help determine which electrical diagram to use. The diagram above is for a 995, not a 990. Assuming the tractor is a 1974 by the title. 1979 and earlier have a starter/generator so the schematic is listed below. 


If the key switch has been changed, it may be the wrong one for this tractor. This is a common error. Was a new switch installed?


Are you familiar with the use of a volt meter or 12v test light? Tell and show us what you have done to check the lights and charging.

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Edited by VTXrider, November 17, 2016 - 07:36 AM.

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#8 glgrumpy OFFLINE  


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Posted November 26, 2016 - 01:23 PM

Many of these tractors have a breaker mounted to the bar going from dash to grill top, near driver end, kinda upside down. Two wires into it. I've found them to be bad or troublesome. Try bypassing that to test.

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#9 ducky OFFLINE  


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Posted November 26, 2016 - 02:12 PM

As boyscout stated you are at the right place.


I suspect a bad Amp meter (OPEN).  Use a test light and check both terminals for power.  Hook test light to B- and probe both side of the Amp meter. If you have power on one side and not the other the meter is (OPEN) and needs replacement.


I am going according to the schematic you posted.  There does seem to be a question as to if this is the correct one.  Please verify it is the correct one and let us know for sure.

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#10 Sawdust OFFLINE  

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Posted December 30, 2016 - 01:11 PM

When I done my MTD 990 I wasn't getting any power to the amp gauge at all. It was my breaker that's mounted under the flat support bar from the grill to the dash. I agree if your getting power to the amp meter & not out replace your amp gauge.

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#11 FarmKing74 OFFLINE  

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Posted October 05, 2017 - 07:34 PM

Guys thanks for all the advice.  I am using the diagram from VTXrider as it seems to match not only the way it was originally wired but the age. So now my problem is that whenever I try to start it it blows the 30 amp fuse connection tied to one side of the amp meter.  I am going to try changing the amp meter which at this point aside from the generator (which has been bench tested and rebuilt) is the only original part left in the electrical system. I have included pics 

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#12 boyscout862 OFFLINE  

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Posted October 06, 2017 - 07:06 AM

If you are blowing the fuse when you try to start it, then I suspect a short in the starting circuit. You need to disconnect the battery and do some testing with an ohm meter to find the short. Good Luck, Rick