Gtenn

Welcome aboard !  That's an interesting scenario. Corolla mechanical & electrical component parts, into a Morris Minor.

Most of us here in Australia, of mature age, remember Morris Minors well; & probably had one at some time, in their early life.  I only will answer your query, if You send us some pictures of your build !   Only joking, but would love to see some pics. Photos tell a thousand words, so they say.

I am guessing, the wiring diagram, you are referring to; is the one in the following post.

https://www.rollaclub.com/board/topic/84897-ke70-headlights-not-working-from-relay/#comment-735796 

As I pointed out in the description, in that post, you cannot rely on the official Toyota wire colours on their manual diagrams, so that can throw you off, if You are probing for a voltage on only a particular colour wire, but that wire on the wiring diagram, is actually using a different current.  I trust you have a simple voltage tester probe, so you can work your way through the circuit, & eventually solve the issue.

My gut feeling is, that you have a faulty light switch in the steering column, that You have transposed.  The headlights were reknown for burning this contact out, as having no head light relay, the contact in the steering wheel stork, carried the full headlight current, & either melted or burnt out.

I'm presuming, all the tail light circuits are working, & it is just the head lights, that are "no go" ?

Clip your test light probe lead to a good earth, start at the battery positive (+ve) terminal, & work your way through the circuit, until, you don't get the test light illuminating.  You've then found the issue.

Trust that assists.

Cheers Banjo