640 Ignition button

[Tinkerer]

My 640's ignition button seems to have went belley up on me. I replaced the starter relay (solenoid) and now if will do nothing when I push the button. I can start it by jumping across the poles of the relay, and it runs all day that way, but the button doesn't work. This is a 6 volt system. Can this button be replaced? It seems to be part of the transmission cover, not a separate piece.

 

[jinman]

Did you replace the solenoid with one designed for a 6-volt positive ground system? I believe your original starter solenoid whas "looking" for a ground to energize the contacts. Many of the new solenoids are grounded through the body and need the opposite polarity through the contact. If you are using a 12-volt solenoid, it may not operate at all with 6-volts. I don't have everything with me right now, but tonight I can look up your system in my repair manual and send you a scan of the electrical system to use in troubleshooting. Do you have a VOM to use to check for continuity?

One other thing you can do to check the starter switch operation that doesn't require a VOM to check...
Put your tractor in neutral and then short the terminal on the side of the starter switch to ground. If the solenoid energizes and the starter operates, you could have a bad starter button switch. If nothing happens, your problem is something else...probably the solenoid wiring as I first noted.

 

[Soundguy]

If the 640 uses the same thumb switch on the tranny cover as my 8N and NAA, then yes it is replaceable.. you have to pull the tranny cover though.. watch for a small ball and spring when you pull the cover. The switch can be had from tractor supply.

However, the other poster was correct. the thumb switch only provides a connection to ground. The oem 6v 3 terminal starter solenoid is internally hot, assuming you hooked it up correctly, I.e. with the small terminal pointed at the tractor.. not pointed out where you can get to it easier. When you hit the thumb switch you are grounding the small terminal.

That makes it easy to test with a jumper wire from ground to the third terminal.

If you have a newer style relay say a 4postone.. if it is an isolated one.. you can still make it work... 1 post to power ( whatever polarity you are using.. probably - if it is still a 6v+grnd ) the other post to the thumb switch that completes the circuit when you push it. Keep in mind that the thumb switch is neutral safety interlocked, meaning it will only function when the tranny is in neutral.

hope this helps.

Soundguy

 

[jinman]

Well, Kirt, when you logon again I think you will have all the info you need to find your problem. At least, I hope so. Between me and Soundguy, we will ensure you have a case of information overload. /forums/images/graemlins/laugh.gif Anyhow, I've got three attachments to help you out and the first one is a schematic of your electrical system attached to this message.

 

[jinman]

Transmission cover assy. with starter switch.

 

[jinman]

The ideal book to have for owners of old Fords. It should still be available from your New Holland dealer. I bought this one in 1996, but I'd bet it's still in print. I believe it was less than $25.00 and it's over 1" thick.

 

[Tinkerer]

Thanks for the infoguys, I am printing off your posts and attachments right now. The solenoid is for a 6v system, I made sure of that when I bought it. There is a tractor salvage yard/parts place about 10 miles from here, that is where I got the solenoid. Entirely possible I wired it up wrong, in fact it is likely /forums/images/graemlins/shocked.gif

On a lighter note, the tractor still runs great when I get it started, I am using it to move a MOUNTAIN of dirt from our new basement and brush hogged about 3 acres this afternoon. I do need to get the manual you speak of, right noe I have only the ITT manual, and I believe them to be somewhat limited in their usefulness.

 

[slowrev]

Yeah the IT manuals are better than nothing, but that is about all.