7040 Alternator Wiring
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=187992
Printed Date: 22 Jun 2025 at 7:43pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: 7040 Alternator Wiring
Posted By: Red Bank
Subject: 7040 Alternator Wiring
Date Posted: 01 May 2022 at 3:22pm
| On the two prong plug one side is constant 12 volt and the other is ignition fed 12 volt? Where does the ignition 12 volt feed come from? The ignition switch or the battery warning light circuit board,. The past two years I have started the tractor and taken a cotter pin and jumped the two prong plug to energize the alternator to charge. Wanting to fix it the right way. |
Replies:
Posted By: steve(ill)
Date Posted: 01 May 2022 at 4:57pm
|
RED... i know NOTHING about the 7040 wiring, but it sounds similar operation to the DELCO alternators... There are two spade terminals and ONE is always hot and the OTHER has almost 12 volts while running.. You say that you "TOUCH" the terminal and it starts to charge ... You dont have to LEAVE the 12 volts on ? .... In the normal system, the wire has a light bulb or resistor that drops the voltage SLIGHTLY and starts the charge, but the voltage STAYS on the terminal as you operator.. It normally comes from the Ignition switch, but has a dropping resistor , bulb , or diode in the line... Apparently you dont need too much of a drop in voltage if you can touch it to get it to start. the generic story is the wiring normally looks something like this.... unless someone has a SPECIFIC diagram.  ------------- Like them all, but love the "B"s. |
Posted By: Red Bank
Date Posted: 01 May 2022 at 5:00pm
| Yes I take a cotter pin and touch the terminals together in the plug and it will charge until I cut the tractor off, that also energizes the alternator and lets the tach work also, usually that is what reminds me to get out and jump it across is so the tach will work. |
Posted By: steve(ill)
Date Posted: 01 May 2022 at 6:03pm
|
I dont think it would hurt to leave the 12 volts on the terminal as you run... BUT, it needs to shut off with the SWITCH when the tractor is not running.
so this is one of those alternators that powers the TACH with an electrical signal while running ? ------------- How does a tachometer work off an alternator? Electronic tachometers work by counting pulses generated by the ignition system, alternator, tach signal generator, or magnetic pickup sender. The tach is hooked up to +12VDC, Ground, and one of the signal sources listed above. ------------- Like them all, but love the "B"s. |
Posted By: Red Bank
Date Posted: 01 May 2022 at 6:50pm
| Yes alternator has post on rear of the case for tachometer wire but the tach will not work until you cross the two terminals in the plug but you only have to briefly touch them together for it to start the alternator working both tach and charging. |
Posted By: steve(ill)
Date Posted: 01 May 2022 at 6:53pm
|
you could use a toggle switch if you just want to momentary touch it... but i dont think that is the way it was originally connected.. I think the IGN switch turns it ON when motor is running. ------------- Like them all, but love the "B"s. |
Posted By: Red Bank
Date Posted: 01 May 2022 at 6:55pm
| I thought about doing that if I can’t figure out the wiring. But that wire goes back into the dash and I was wondering where it goes before I take the dash apart. |
Posted By: MACK
Date Posted: 01 May 2022 at 9:21pm
| I would disconnect the wire plugins at right rear of engine, clean and blow dirt out, then use some electrical cleaner and reconnect. Be a good place to start. MACK |