Taking the plunge

Lets try some very basic tests.. Pull the yellow wire off of the startwe relay. Put a test light between it and ground. With the fuse in question removed,
turn the key to start and verify test light and yellow wire all conneted.
Allow the switch to rest in run position and verify test light is now off.
Now lets connect that fuse to its holders and see if the test light comes on. If is does not then I'll scratch my head while you rewire the whole car.
If the test light does come on your goal will be to make it go off.
You will find that yellow wire has broken insulation somewhere and touching another wire that is on your fused circuit. That yellow wire runs from keyed switch, to bulkhead connector and out to the relay / test light .
On some models there was a seat belt safety interlock that would interupt the start signal. I dont recall if it was on the yellow wire side of the relay or the brown wire side. Your car may not even have this crap. Just thought it worth mentioning. Good luck . I'll be back