Hey all...

After 13 yrs of all original 6v pos grnd I am in the process of converting my '50 F-1 Flathead V8 to 12 volt neg grnd. I have my generator converted, put in Pertronix Igintor II electronic ignition and Flame Thrower II coil. I have installed a 12 volt solenoid but was wondering if it mattered which side of the solenoid I hook up the battery and starter cables. Originally the battery was on the drivers side post and starter on the passengers post. But on later model '60s-70s Ford it's the other way around. The reason I ask is the original wiring to the dash is on the driver's side post and won't reach to the other side.

 

The starter "solenoid" is really a relay and the two posts are connected when the relay energizes. It doesn't make any difference which posts the wires are on, as long as you keep them together like they were. One post gets all the power wires from the battery and to the other places that get the 12 volts without starting the truck. The other side goes to the starter.

 

See below. If your solenoid is original, the starter button grounds it to energize. So the battery cable needs to be on the original side.

 

A similar thread from a while back. It does matter.

https://www.ford-trucks.com/forums/1...2-f1-help.html

 

Ah, I stand corrected. I didn't realize the one post was attached to the coil internally. I should have looked at my wiring diagram before I shot my mouth off.

Sorry for the misinformation. Thanks for correcting that Ross.

But the OP is for a 12volt solenoid. Don't they have two small posts, pos and neg to energize the relay?

 

Thanks for all the help... I read the recommended post and studied the diagrams....BUT... my simple mind needs to understand something. Can't electricity flow either way thru the solenoid and simply close the circuit when energized and not matter which way the big posts are connected? Doesn't the magnetic field close the switch thusly it could be hooked up either way???

Thanx guys for the patience in explaining your answers and helping me "grasp" this. I'm more than ok with hooking it up the way described in your answers but I'm just one of those guys that really likes to understand everything when I do it. Please bear with me on this.

 

Sorry, either I misread your original post or you edited it, I didn't see that you now have a 12v solenoid (I assume a 4-post later model?) They operate differently. Power is put INTO the small "S" terminal to energize the solenoid. With those, it still matters which post you use for what, because the "I" post would be hot all the time if backwards (you couldn't shut the engine off). But your original '50 starter button won't work, you need the two-terminal '52 and later type (fed off the ignition switch). They are direct replacements.

 

Well, hopefully you realize that I was wrong in saying it doesn't matter which posts hold which wires. Ross has showed diagrams for both 6 volt and 12 volt relays. The post going to the starter has to be the correct post. Sorry for leading you astray...

 

I have a 12 volt solenoid with 4 post. I am NOT running a ballast resistor.

I was going to hook up the small wire to the "S" post and leave the "I" alone... will the original starter switch work wired like that or do I need to try to get a 3 post 12v solenoid(I prefer the original look) to use my original starter switch? I could always get a 2 post starter button if needed.

 

If you are not using a ballast resister I don't think ya need the I post.
It is to give full voltage to the coil while cranking. Then drops out when
running.

 

If you go to link below and look at the second engine picture you can see the solenoid still hooked up in the original factory configuration. The description states it's converted to 12v and you can see the 12v battery and modern radio. So... does this mean the solenoid CAN be hooked up either way...?

http://www.ebay.com/itm/Ford-Other-Pickups-F1-Truck-NO-RESERVE-1949-FORD-F1-PICK-UP-TRUCK-FLATHEAD-V8-3-SPEED-MANUAL-FLOOR-/181260333528?forcerrptr=true&hash=item2a33f531d8&item=181260333528&pt=US_Cars_Trucks

 

As Ross mentioned, and showed in his diagram, if you hook up a 4 post 12v solenoid backwards by swapping the battery and starter connections, your I post will be hot all the time. Even if you don't use it for the ignition, it's a hot wire hanging out in the open waiting for a short to happen. It's not recommended to do that. If you insist on having your wires reversed, turn the solenoid upside down.

In the photo in the ebay link, I see the solenoid as being a 3 post, not having an "I" attachment.

 

I have been following this post for awhile now and realize some wrong information is getting out. The referenced diagram for a 4 post is not the way all 4 posts work (I have never actually seen one that works this way). All that I have seen have the "I" terminal isolated from both large terminals. The solenoids have a large copper washer inside that when the solenoid is engaged makes contact with both large terminals and the "I" terminal.

If the solenoid was wired as shown in the diagram power would flow from the coil through the resistor (if installed) and to the starter. This would either blow the ignition fuse or melt the ignition wires due to the AMP draw of the starter.

I have had solenoids apart, and have just used an OHM meter on a new Ford solenoid from stock to verify this. If you want to check yourself hook a OHM meter from the "I" terminal to each of the large terminals, there will be no continuity.

So starter and battery can be hooked to either large terminal. Crank wire hooks to "S" terminal and if you have a ignition that uses a ballast resistor hook a wire from the "I" terminal to the coil. If you have electronic ignition and do not use a resistor don't use the "I" terminal but do protect it from contact as it wil be hot when cranking

 

Thanx everyone SO MUCH for all the input and advice. I really appreciate it!

I was thinking from my limited knowledge of solenoids that the magnetized field pulled the plunger to close the circuit. I was thinking it wouldn't matter how the solenoid large posts were hooked up to close the plunger. But wanted some verification before I hooked it up like it came from the factory with 6v+.

I just wanted to use all existing wiring without cutting/splicing or moving the solenoid from it's original mounting holes to keep as much of the originality of the truck that is possible. But neither is a necessity... merely a personal preference.

Maybe I will try it both ways and see if it works properly either way and hopefully I won't melt/burn down anything in the process.

 

I stand corrected (again)! It is like below?