Maybe its an older Haynes, mine has it on 12-30.
If you can screwdriver jump the starter and it works, go back a step and confirm 12v going to the ignition switch white/yellow, then to the clutch switch blk/red, then to solenoid as blk/yel.
I have an 87/5speed and i thought the START 12v power came to a blue wire on the pigtail coming from the key switch.
My Haynes says :
wht/yel to ignition switch; then branches to the generator (same color)
in START is a blk/red to clutch switch
from clutch switch a blk/yel to starter solenoid
3 wires relating to generator are:
same wht/yel from branch mentioned above
a blk/wht to distributor
wht/red to insturment panel
What are your wire colors before those non factory splices? Can you trace them with a voltmeter setting that beeps when you touch the contacts together? If so you can run a long pigtail to these unknown wires then use the other side of the meter in the fuse box.