7040 Tach and Alternator Problems
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=158299
Printed Date: 03 May 2024 at 11:58am
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Topic: 7040 Tach and Alternator Problems
Posted By: Blustery Knoll Farm
Subject: 7040 Tach and Alternator Problems
Date Posted: 18 Feb 2019 at 4:16pm
| Trying to get a couple electrical things resolved. When I bought it, the tach didn't work and it only had one battery. I noticed that at low engine speed, the charge light inter intermittently came on unless the lights were on. Today the battery was dead, so I put in two good batteries. Now no charge light. Interestingly, I turned off the key before shutting down the engine and the tach started working. So, where do I start troubleshooting? |
Replies:
Posted By: DougS
Date Posted: 18 Feb 2019 at 5:12pm
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Voltage first. Put a good digital voltmeter across the battery while the engine is running and tell us what you have. I smell an alternator problem - possibly one of the three diodes - but let's start by looking at the charging voltage. |
Posted By: Moneypit
Date Posted: 19 Feb 2019 at 9:08am
| When I bought my 7020 alternator was wired wrong didn’t charge tach didn’t work and I wasn’t smart enough to figure this out until I put new alternator on lol |
Posted By: Blustery Knoll Farm
Date Posted: 19 Feb 2019 at 10:26am
| I was going to swap on the alternator from my 7020, but it's wired up differently. The 7040 has just two wires. |
Posted By: DougS
Date Posted: 19 Feb 2019 at 4:51pm
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I can't help you unless I know what you have now and exactly how you have it wired. I would suggest that you get in touch with a local mechanic who knows his way around wiring - not one who only knows how to plug a device into a diagnostic port on a car. |
Posted By: Blustery Knoll Farm
Date Posted: 19 Feb 2019 at 5:25pm
| I will take a couple pictures and check out put voltage when I get a chance. I guess I should probably get a service manual so I have the diagram. |
Posted By: LB0442
Date Posted: 19 Feb 2019 at 6:23pm
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Here is a post with a wiring diagram. http://www.allischalmers.com/forum/allis-7060-wiring-diagram-schematic_topic139284.html" rel="nofollow - http://www.allischalmers.com/forum/allis-7060-wiring-diagram-schematic_topic139284.html
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Posted By: Blustery Knoll Farm
Date Posted: 18 Apr 2019 at 6:18pm
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Finally getting back to troubleshooting this. I have the manual and wiring diagrams now. My alternator is wired up with two wires. Voltage at the main orange wire at the alternator terminal with the engine running is equal to battery voltage with the engine off. |
Posted By: Lynn Marshall
Date Posted: 18 Apr 2019 at 8:47pm
| This tractor sounds like it has the early Niehoff system on it. Personally,I would just switch it over to a Delco with the tach correcting pulley and the corresponding wiring change. The tachometer head could still bad, but at least it should charge. |
Posted By: GM Guy
Date Posted: 18 Apr 2019 at 11:33pm
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We have a similar issue on a few of them, it seems a dead tach and no charge is the issue, and swapping to an identical known working unit results in no change. What energizes the alternator to charge on these? The issue is had on a 77 maroon with a factory niehoff, and a 74 maroon with the factory Delco. The distinct differences in alternators make me think its tractor wiring related. ------------- Gleaner: the properly engineered and built combine. If you need parts for your Gleaner, we are parting out A's through L2's, so we may be able to help. |
Posted By: Blustery Knoll Farm
Date Posted: 19 Apr 2019 at 1:15am
| My alternator sure looks like a normal one wire Delco alternator, except for the second terminal for the tach. |
Posted By: LB0442
Date Posted: 19 Apr 2019 at 8:23am
| If the current alternator is the delco SI unit and only has 2 wire connections at the plug in the tach will never work correctly (1 for voltage sensing and the second was for gen light), needs to have a 3rd terminal for the stator pulse(tach). That correct delco alternator has all 3 wires on 1 plug. If it originally had the neihoff they had a small battery wire, large charging wire and the tach lead, and I think a case ground, gen light worked off of tach lead. Need to verify what wires you have now, either through wire color or trace the circuit or both. |
Posted By: Steve in NJ
Date Posted: 19 Apr 2019 at 8:49am
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Sounds to me like it could be equipped with a one wire Alternator. If so, most one wires need 1200-1400 rpm in order to excite the regulator to start the charging sequence. With the Headlights on, the rpm might have been close enough for the VR to turn on because of the load put on the VR from the Headlights. Hence, the light on the dash going out. A simple three wire system would work fine on that machine providing you have an "SI" series Delco. Some Niehoff units can be wired the same way... mailto:Steve@B&B" rel="nofollow - Steve@B&B ------------- 39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife |
Posted By: Blustery Knoll Farm
Date Posted: 19 Apr 2019 at 4:31pm
 Here's what I have for wiring. My wiring diagram indicates brown goes to tach and orange to a circuit breaker, then the battery. |
Posted By: Lynn Marshall
Date Posted: 19 Apr 2019 at 6:17pm
| You have a one wire Delco there. If the alternator is charging,the wiring is good,and the tachometer head is good,it should work. The engine speed may not read right if the pulley is not the right size. The harness appears to be from an early Niehoff set up. |
Posted By: GM Guy
Date Posted: 27 May 2019 at 10:00pm
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What is your serial number? 3501 and up is the break between Niehoff and Delco. Some things I found out on our 7040 w/ factory delco (SN 28xx) here recently: Symptoms: No tach, no charge, batteries dying I had a bad alternator. Dont trust parts tractor alternators, they are not magically good all the time. :) Got a Beijing Belt drive off eBay specifically configured for a 7040 (search 7040 Allis Alternator) with the tach stud, back brace mount, etc. Being Chinese I am not expecting much, but we'll see. My bad draw? Cooked Circuit breakers on the firewall. presumably when the chassis harness got pinched by the battery tray due to incorrect routing by the previous owner. My buddy who can solder a whole lot better than I put the harness back together. He fixed it months ago when I was in the area putting a new positive cable on and converting the grounds to stud type so I can use truck batteries, but we didnt do anything about the breakers. They are on ebay for like 6 bucks, Agco wants 30 bucks or so, also check a big truck shop or a well stocked Napa, as the offset 2 hole mounting tab is quite odd. I had it all going and working flawlessly, then I hit the road to go a quick spin to churn up the oil for a rear end/ hyd. system change and lost the tach. got a tiny little whisp of smoke too. I now have no hyd. restriction and hyd temp (lower row, outer left and outer right bulbs on the individual bulb system) this issue cropped up last year as well. So, tonight I tore the dash apart (whoever designed this dash and front console needed beat like a punching bag...) , and I think I am going to drop the tach out, as according to the diagram there is a terminal on the bottom that feeds the purple wires going to the idiot lights. I am hoping its rubbing and grounding to the case and causing my loss of 2 idiot lights and tach. we'll see! As far as a 3500 and down SN tractor's factory wiring, there is a green wire that comes off the battery side of the circuit breakers, it and a brown wire from the starter solenoid are the only ones on there, other side of the breaker has 2 cab feeds. That green wire goes down the engine harness and to the alternator's pin 2. There is also a black wire and another green wire, they go to pin 1. Green pin 2 is constantly hot. The brown wire is for the tach, the proper alternator has a little stud sticking out this connector goes to. ------------- Gleaner: the properly engineered and built combine. If you need parts for your Gleaner, we are parting out A's through L2's, so we may be able to help. |
Posted By: johnnymopo
Date Posted: 27 May 2019 at 11:44pm
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You all will probably laugh but I thought I would share my experience when I was a kid 20 years ago: I got a 7060 with a bad alternator. The Agco one was out of my budget but I was able to get one from the local carquest store - I believe an alternator for an old GM pickup. Of course no tach wire, so I split the alternator and attached a wire to one leg input to the rectifier. Worked like magic for the next 10 years! |
Posted By: Blustery Knoll Farm
Date Posted: 04 May 2022 at 4:59pm
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Just bringing this thread back from the dead as I was in the dash getting some warning light bulbs changed, so I did some probing with a test light per the service manual instructions. Alternator has been charging fine for the last couple years. With the engine running and key on, my test light comes on when connected to the AC tap terminal (brown wire) and the + terminal at the bottom. Meanwhile the tach reads 500 RPM and doesn't change with engine speed. If I turn the key off, the tach reads correctly, except there's a spot around 1800 RPM where it sticks until I throttle past 2000. No voltage at the + terminal at the bottom, but 12v at the alternator tap terminal. Not a huge deal to run it this way as I can check engine speed by flipping the key off, but... Is the tach unit likely the problem? Also, the hour meter does not work. |