Don't take what i say as gospel--but without looking--does the switch black & black/white connect when off & disconnect when on.
If so, & black from the switch goes into a loom black, & black/white from the loom goes into 'that' black/white on the switch it should stop & go.
I think?.
That's providing black/white finds its way to the loom wire powering the coil. Which is likely only black at the coil.
Happy to be corrected [scalded].

"The black wire coming from the key switch is in a 4 wire plug connected to the main harness, doesn't it ground through the harness at the black wire I have connected from the harness at the coil mount?"

I don't know, what I'm saying is the black into the key should connect to a ground.  You'll need to check/test that. 

"If I'm understanding you correctly I should plug the black/white into the triple black female that goes to coil ground?...."

No.

You might be overthinking this.  The goal here is very simple.  Look at the diagram I posted. 

Do you have a black/white coming out of the harness near the key switch?  That should be the wire that tees into the wire between the points and the ignition coil.  When that wire is connected to ground, NO MORE SPARK. 

The black/white coming from the key switch connects to the black/white coming out of the harness at the key switch.  With the key off, the switch black/white connects to the switch black.  If the switch black is plugged into a good ground, then with key off, spark will be killed. 

So try this...  temporarily connect the black/white coming out of the wiring harness near the key switch to a good ground. That bypasses the switch completely.  Now you should have no spark.  If grounding the harness black/white kills the spark, then something is wrong with key switch or the black out of the key switch is not connected to a good ground.

 

I've forgotten if its running--but if running just touch the black/white to earth briefly to see if it stops, just tap it stop go.
Just shorts the source coil etc from the mag in a convoluted way. Won't get a shock. Might get a low voltage spark? if scratching it not solid touching earth.

Has someone been into the loom & repaired things but got their wires crossed [so to speak] & in reality.

Good morning Everyone, thank you for your responses, my brain is doing somersaults, I'm gonna read and re read what you guys are saying , I wish I had a Tesla brain , but I'm just a carpenter . My wire loom is a brand new one from Enduro Doctor , the kill switch is a new repop 2 wire , the key switch is a mix, the top half is the original from the 74 dt250a, the bottom half is from a 76 DT400 and does function when it comes to operating the tailights , the horn and the turn signals, I did try to test both switches , key and kill for continuity by connecting the leads to the wires and turning the switches on and off and the meter was 0.00 when switches were off and when I turned the switches on the meter said just the number 1.
The bike does start and run I drove it around my yard for almost a mile now.
I am thankful you all are trying to help me ,
I'll check back after I do what you all are suggesting I try and let you know how I'm coming along.
Thank you all
John

The secondary coil is bolted to the frame , I cleaned the threads of powdercoat to assure a good ground , I did not clean powdercoat from the engine mounts , I did notice on the secondary coil, the small black wire coming from it ( black) seems loose where it enters the coil , it is the original 50 year old coil. I was going to replace it but didn't.
is the small black wire entering the secondary coil a ground wire ? And if it's not connecting good , since is feels loose, would that stop the kill or key switches from working? Also because I did not clean off powdercoat from engine mounts would that cause the switches not to work ?
I did look at the diagram MarkT posted its confusing to to try and figure out a way to make a T to somehow interrupt the flow of current , one might think this is all handled through the new harness /loom by simply plugging in the individual different colored wires to their mated same colored wires from the different components . On the new wire loom as it runs along the frame of the bike under the gas tank there are 2 black wires near the secondary coil one has a ring connector and the other a female end I plugged that one into the secondary coil and connected the other ring connector to the mount for the secondary coil . The other wires coming out of the loom ahead of those two black wires at the secondary coil are for the flasher unit, the rectifier and the key switch plug .

Posting pictures would help you can use google photos,Imgur,dropbox etc 

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No. Do not mess with that little wire going into the coil! That's the little wire from the points and you will lose spark if you break it. It is NOT a ground. The wire that tees into that little wire going into the coil gets connected to ground to kill the spark.

The "tee" basically shorts the wire from points to the coil to ground when you want to shut off the engine.

I don't know what else to say... I might be making this worse so I'll let someone else try to explain.

I tried to post some by copy and paste, didn't think it would work. I'm terrible at computer too.