Actually I need to refine the testing. With the battery disconnected...

1. Remove the R wire from the relay and see if you have continuity between the R and WR wires. If you do, it might be that the combo switch is not opening the contacts.
2. If #1 shows continuity, disconnect the wire going into the combo switch and re-test continuity between the R & WR wires. If you no longer have continuity, that implicates the combo switch. If you still have continuity, you have a wiring issue.
3. If #1 shows no continuity, check for continuity between the B & S terminals with the R wire still disconnected. If you have continuity there, the relay has a problem. 

Well, I identified the problem causing the relay to click.

I had one of the dash harness connectors to the fuse box on upside down, and since I didn’t check it against what I plugged it into, all those wires were going to the wrong things. I figured this out after finding no continuity from Steve’s diagnosis process above and trying to figure out where the red ground wire might connect to power.

I pulled the connector and fixed that. The relay no longer clicks when the battery is connected, so ON TO THE NEXT!

Edited January 28Jan 28 by Matthew Abate

@SteveJ He is an amazing guy when it comes to wiring issues.

I'm glad you got that sorted out. Being able to eliminate possible problems help you move on to find the real cause.

Alright. One problem solved, two problems uncovered. 🙄

The headlight relay is all wired up.

Once I finished this I started testing. I got nothing when set to OFF (good), nothing when set to LOW (bad), and the relay clicked when set to HIGH (good).

I pulled out the meter and checked continuity on the relay with the wires on. s1 to B, s2 to B, s1 to s2 all connect as they should. S to L1, S to L2, and L1 to L2 all connect as they should.

My continuity from s1 and s2 to the two dash harness wires at the combo switch is good for both R/b and R/w.

But now I’m getting no continuity between any of the three wires coming out of the combo switch in ANY position (Off, Low, or High). That doesn’t make sense because High was tripping the relay before.

Then I went to check voltage running through the relay and now I’m getting nothing at the relay. So I checked voltage from the battery (12.67) and voltage coming out of the engine harness in the cabin from the alternator and starter wires. 0.06 volts.

The only thing I can think of is that the fusible link blew. I need to do kid bedtime stuff now so I’ll check that in the morning.

Edited January 29Jan 29 by Matthew Abate

Are you using the factory combo switch? You might check there first

Yes. As far as I can tell it is a ‘73 combo switch. It was fine after I rebuilt it. Now I’m not getting any continuity. Maybe something wasn’t secure inside and fell out of place. Maybe I’m tired and had the multimeter set wrong.

Edited January 29Jan 29 by Matthew Abate

Checked the fusible link this morning. It’s fine. One thing I realized is that I’m thinking of the combo switch wrong. It’s Off, PARK, Headlights. Not Off, Low, High. I’ll start over with my testing. There may be nothing wrong with the wiring.

 

That doesn’t explain the low voltage and lack of continuity at the switch, though.

Edited January 29Jan 29 by Matthew Abate

By the way, here's the truth table for the 73 combo switch:

So the red wire should have voltage to ground when the headlight switch is on.

Have you verified you are using a good ground point when measuring voltage?

I thought my grounds were solid but maybe not. I can’t work on it tonight but tomorrow I’ll go around and check. Im confident about everything in the engine bay. Inside the cabin might be less solid.

Well, apparently there was nothing wrong. User error? I just tested everything and the only relay not clicking is the intermittent relay.

I can hear the rear fuel pump running (that may need some sound proofing), the headlight relay is switching for both low and high beams. The horn relay is clicking, and the accessory relay is clicking.

I have another intermittent relay, so if I’m not getting any voltage at the wiper motor plug I’m going to swap them to see if that makes a difference.

I still need to check the two flashers, the choke/heater relay, and the buzzer, but I don’t have enough of the components assembled to do that yet. Otherwise it’s on to the next step of checking voltage at all of the light connectors. After that I’ll see if it starts from the key.

Edited January 31Jan 31 by Matthew Abate

I did a quick sketch of the wiring for the AILD-1 PWM. I'm waiting for a fuse holder in the mail and then I'll make a sub-harness for it.

 

Edited February 9Feb 9 by Matthew Abate