HELP - Starter Runs Continuously on Restoration Start Up.

OK, Finished Resto on my 57 Ford 850. 12 V conversion was part of resto. Went to crank engine for first time as part of process to set timing. Here's where it gets too weird. Connected battery, pressed starter button and engine turns over, release starter button and starter continues to turn until I remove battery cables. So, I removed the starter wire from the button, re-connected the battery cables, touched the starter wire to the starer button and pressed down the button, and starter starts. I then disconnected the starter switch wire and starter continues to run until I disconnect the battery cables again. So, it is not a faulty starter switch. I used YT archives diagrams for 12 V conversion. Replaced coil, battery, all bulbs, all wiring, and put in a 1 wire 12 V alt. I removed the voltage regulator. The starter solenoid was not replaced. Looking at the solenoid installed on the tractor the left terminal goes to the starter. The bottom terminal goes to the starter button, and the right terminal goes to the Battery + terminal with another wire going to the amp-meter. This same amp-meter terminal post also goes to the hot side of the terminal block. The one wire Alt goes to the other post of the amp-meter. All the while during this test, the ignition key was off and removed from the ignition switch. I double checked to make sure no wires or crimps were touching the frame. So, where did I mess up??? Is my solenoid or starter rely faulty even though it worked fine on the 6 V system prior to resto? Should the wire from the right side of the relay go somewhere other than the hot side of the terminal block? Not my first resto, not my first rewiring project, but cant figure this one! Any suggestions?? Cant do anything else till I get this solved. Thanks all, Larry.

You need a 12 volt relay (the part you call the solenoid).

Here's a picture of 3 different relays: 6, 12, & 24 volt styles, note they all look the same on the outside. The only difference is the internal resistance of the coil to suit the operating voltage. Also note that these are NOT the relays for your tractor - it is for illustration only.

To go along with what Bern said, the solenoid that will work is ST-542.

Thanks guys. The reason I did not replace the solenoid / relay is that nowhere in the archives does it suggest this is necessary. Also, the Steiner Catalogue clearly states that their Ford replacement units work for both 6 & 12 volt systems. Also, other restoration parts companies indicate their units work for Ford models that were 6 volt and other later models that came with 12 volt systems right from the factory. So, I just assumed my relay did not need to be replaced. SO, I will replace with unit as you suggest and keep my fingers crossed. Thanks again, I really appreciate your help, Larry.

Had same issue. Replaced solenoid with correct solenoid, and problem went away. I believe my solenoid went suddenly kaboom inside after working well for many years. Totally freaked me out but calmed down after i purchased the correct grounded relay. (Just kidding about totally freaking out, just adding that for dramatic effect).