503 DCDI still won't cut off

[Tracy]

I attached two wires directly to the mag kill wires, a third wire
bolted straight to the engine itself for ground.

Then I started the plane and rev'd it up to 5,000 without warm up and
hooked the wires together and it cut off, then I let it warm up for
two minutes at 2,000, hooked the wires up at 2,000 after two minutes
and nothing, engine keeps running.

Leave wires hooked together and reduce throttle to the rough idle and
engine then shuts down (because the wires are hooked together, other
wise it would keep idling).

Put a meter on AC, one kill wire has 1.8 VAC and the other has 28 VAC
(using the third wire to engine ground as reference). RPM does not
increase or decrease the 28 VAC reading.

Then I noticed the kill wire with 1.8 VAC would sporadically become
28VAC for no apparent reason and then go back to 1.8 VAC when it
decided too, no relation to engine RPM for this VAC change.

Any ideas, I'm thinking bad Ebox now, or a bad mag/coil ?

I don't want to order a lot of stuff I don't need, so if you KNOW what
may be the problem let me know.