You say "OL" in one direction and about .457 volts in the other. Are you putting DC volts through it or do you mean .457ohms. Not sure what DC would do as takes AC in from the mag.

Thanks MarkT.  It's settled then; I do NOT know how to read a wiring diagram...LOL.  This whole undertaking has become so damned frustrating.  When I bought a bike knowing that "the lights don't work"...I never imagined it would be this difficult to sort it all out.  I'm going to start the bike with the original rectifier (which appears to test good) connected tomorrow and see what happens.  I've now looked at power wires and grounds for all four turn signals and the horn, replaced all the wiring for the brake/tail light assembly, installed a new stator & coils and looked over the wiring in the headlight bucket where everything looks good.  I'm hoping things work well tomorrow.  If not, I have another replacement rectifier coming in a few days.  Other than that, the only other thing I can imagine doing is redoing or replacing the entire wiring harness.  As much as I'd hate to do so, I think I'd be more inclined to sell the bike before I did that...having owned it for less than a month.  As much as I'd like for something obvious that I somehow missed to jump out in front of me in one of those "Duh!" moments, I'm beginning to think this just isn't going to end well.  But until I decide to give up on it, I'll remain hopeful.  Thanks again for all your help guys.

RT325, I was using the instructions from DEET here: www.yamaha-enduros.com/index.php/forums/...a-rectifier-or-diode
which mention a "voltage drop" when testing the rectifier.  Now you have me wondering if I in fact tested it incorrectly, as I did NOT have it installed in the bike when I tested it.  The seller of the rectifier I bought wrote the following to me:
Inside a half-wave rectifier there is only 1 part, a diode. It should let voltage pass through one way and not the other. Set the meter to diode mode and put the red lead on the ~ and the black lead on +. It should beep and read around half a volt (reading depends on the meter). Switch the leads and it should read nothing.
So...now I'm confused even more.  Does "diode mode" on the meter reflect voltage drop, resistance, or something else? 

I'd better go read the link. I only just test on ohms & get connection one way & nothing the other. That's about as far advanced as i an lol--not very. I'll go check one now if i can find one. Mind you never had much reason to test. Have had a couple a terminal broke off or corroded off so just a straight replacement job. actually the one i was going to find, come to think, i'm using on my TRX300 Honda Quad & no regulator but think i'm only using one wire from alternator with one earthed, bit like a yamaha mag lighting charging coil. Just a simple system as doesn't take much to keep the battery up for daylight use. Unregulated i know but doesn't charge higher than safe at revs just on one wire. Been like it for about a year since it melted the back out of the regulator/rectifier due to internal fault. Rectifiers aren't voltage specific as far as i know as my quad is 12 volt & the Yamaha it came off was 6 of course.

To be sure, you need to read the meter manual. 

Some digital meters have a "diode test" mode that applies a small current/voltage to the diode.  The readings you got sound about right for a meter with a diode test mode.  No current flow in one direction and reverse the probes (polarity) and the current flows and you can read the small voltage.  It's a one-way valve basically. 

You can also test a diode with an ohmmeter which is what I do because I don't have a fancy meter with a diode test mode...  well, actually I think I have a little Harbor Freight freebee meter that has it but I've never tried it.  It sounds like RT325 is describing the old fashioned way with an ohmmeter.  

Couple or 3 pics take no notice of my lead clips + doesn't mean +. So nothing oneway & about 4.5 ohms the other. My meter won't zero past 1 ohm. & pic of rectifier on my quad. We're in lockdown for 3 days, Covid kicking off but not down our way "in NZ" but up Auckland mainly with 7 days & maybe extended. Plenty to do in the shed lol.

Yep...the two meters I used today (mine and a friend's) both had a specific "diode test" position.  I was wondering about the possibility of the meter's battery itself putting a small amount of current through the rectifier; I guess I now know that's how those meters work.  I may try the ohm meter method tomorrow just to see what I get.  Thank you all again.

Actually, must confess, i've never tested one for value until today. Just gone yep nothing oneway & passes something other way so just thought of it as ok. Worked for me.

Well guys, it looks like I'm VERY close to diagnosing and repairing all of the electrical issues on my bike.  The bike starts and runs fine.  It charges at about 8 volts at idle. The new rectifier works fine and remains cool to the touch.  Headlight works (low and high beam) and the horn,  tail light & brake light work as well.  I have only ONE issue remaining and believe it or not...it just popped up today.  My turn signals are the problem.  When I move the switch to activate the LEFT signals, they stay on solid (do not flash) and the indicator light in the tach lights up solid as well (no flashing).  When I move the switch to activate the RIGHT signals, they also stay on solid (no flashing) and the indicator light in the tach DOES NOT COME ON AT ALL.  All grounds to all four turn signals are spotless/corrosion-free.  Any ideas as to what might cause this or where to look first?  Thanks again for your help!

First thought, do the bulb wattage match the relay. Here were i am we might have 8 watt relay which will have 8 watt X 2 + 3. Meaning two 8watt bulbs plus a 3 watt dash bulb. But if you had a 17 watt relay 'common here too' & have 8 watt bulbs it'll just glow & not flash. That probably an extreme example but if you get too far below recommended they won't flash. you can go a little higher wattage for a faster flash but not too much higher.
Ok i think i've wasted computer ink writing that lol as shoulda taken notice of your right side tach bulb not glowing--so i'm lost. Back to basics & check wiring connections from the tach bulb--is the green & brown from 'that' go to correct color green & brown--dark colors.