Fast ongoing clicking after removing Neg battery cables

[Simplicity]

I've been wrangling a no crank situation. If I jump the start relay, the bus fires right up and runs great.

In doing some trouble shooting, I disconnected the two large NEG starter battery wires #1 & #3 (see picture).

If I remove #3, all is fine.

When I remove #1, I get a really fast clicking from what appears to be the ECM.

I understand the ECM has some capacitors in it for I believe the injectors, yet when I remove the NEG starting battery wires, everything should go dead.

To stop the clicking, I simply put #1 back on it's battery post.

Questions:
Why would something be clicking?
Could it have any relation to the no crank situation.

I need to figure this out so I can disconnect the ECM connections and test some ECM terminals, and I won't test without disconnecting the starting batteries.

Thanks.

[Danjo]

When you remove 1 is 2 still connected to it and is 3 still connected? If you remove both 1 and 3 at the same time does it click?

[Simplicity]

#2 remains connected the entire time.

No clicking when #3 is disconnected.
and #1 is connected.

Clicking starts when #1 & #3 both disconnected.

I have not done any further testing than that.

[Danjo]

Secret 3rd battery?

IDK. I’m out!

[cadillackid]

I have to take ALL the cables off or unplug the white connector.. there is a supplementary ground in that small white wire..

otherwise i get the clicking

[dbsoundman]

I agree with Cadillac, you have to remove ALL the negative wires going out of the battery box, even the little ones. I disconnected the big cables once thinking I had the battery disconnected, then I pulled an emergency hatch lever…lights still came on! Whoops.

[Simplicity]

Ug, that white wire was tucked and taped in a way I couldn't see it. That makes total sense. I'm sure that's it. Thanks!