Scott,
Wow! These pictures give us much more to discuss... Did you do the repower yourself, or did a prior owner do it?
The serial number of your 316 shows it to be a 1984 model year unit, which would originally have had the B-series engine with the separate solenoid on the firewall. Your frame appears to be cut out for the presently shown Performer 20XLS (as was fitted in Wheel Horse tractors and some others ...) The P-series engines that were fitted in later 316 and 318 tractors were a slightly different version with a starter that had the solenoid hanging down as the illustrations in my posts above -- and cutting a clearance rectangle the floor of the frame to clear those solenoids is much less structurally intrusive than cutting into the side rail.
I cannot tell exactly how your tractor is wired presently, but the starter in the picture above is definitely of the "solenoid-shift" variety...so that solenoid must be energized to engage the pinion gear with the flywheel ring gear, as well as to provide the high current path to power the starter motor itself.
I guess it is possible that a 'creative' approach was taken by the prior owner that connected the solenoids in SERIES -- but if that were the case the switched high current lead from the firewall mounted solenoid that would have gone directly to the B-series starter must now go to the P-series' solenoid terminal "B" and to work at all the "A" terminal of that starter-mounted solenoid would have to be connected permanently to that B post as well. All VERY ODD -- and if I were trying to fix this unnecessary series solenoid configuration, I would convert everything to use only the solenoid on the starter, and remove the separate solenoid from the wiring altogether. There are lots of careful steps needed to do that however...maybe in another post.
There are other subtle issues in swapping a P-series engine into a B-series tractor, like a different length drive-shaft (but maybe the conversion that was done on your 316 included the re-use of the B-series flywheel...)
What more can you tell us about the history of your tractor and its conversion to the Performer 20 engine???
...by the way, I presume that the separate solenoid shown in your first picture above was taken off the firewall for picture taking purposes, right? Here is a component locator for a 318 that also applies generically to your 316:
Chuck
316 Starting Circuit.pdf
