I understand I could be seeing this all wrong, so appreciate any assistance.

I have a marine battery box with a motorcycle battery in it. It allows me to connect up multiple devices via DC plug or terminal. The battery box was meant to feed lights and other accessories completely separate from the main battery. I have deliberate reasons for not connecting the batteries up in parallel.

I had installed two sets of LED lights in my UTV and thought I was good. Then one set went out overnight. Thinking it was just an old unit not built for outdoor use, I trashed the build (which took about 4 hours). Then the second set of lights, rugged outdoor rock lights, got very DIM. I didn't expect the LED draw to drain the battery like that; so, I then hooked up my battery charger to the exposed terminals and charged the battery. Charged in a short period of time, the brightness of the LEDs did not come back. I began to suspect I had hooked things up wrong and fried either the wiring or the LED control module.

I ordered a second identical set of lights. I pulled one LED run and plugged it into the control module which was plugged into a DC port of the battery box. Results were identically bright for old and new LEDs. Hmmm, was I wrong about the control module being fried? Before I tested that theory, both lights were dim the next morning. I then hooked up my charger (known good) to the exposed terminals, and as soon as pushed the charge button, both LEDs got BRIGHT.

I am going to test the old control module as soon as its cool enough. I am confused about my mixed results.

This is when I decided to become a student again in electrical engineering. Please see attached. If I decided to hook up directly to the 12V source, does the attached diagram make sense given the involved elements?

In the diagrams, the "ground" are separate connections. Can they all be grounded to the same gound? in this case likely the roll bar. Could they be grounded to the black terminal of the battery box?

 

Can they all be grounded to the same gound?

Yes.

I suspect that you might not have a good ground connection

 

Yes.

I suspect that you might not have a good ground connection

Now that you state that, I have nothing going from the ground (black) of the motorcycle battery to the roll bar.

 

In the diagrams, the "ground" are separate connections. Can they all be grounded to the same gound?

That would be the typical case. You separate them only when you require galvanic isolation between circuits.

Could they be grounded to the black terminal of the battery box?

In most cases, yes.

Now that you state that, I have nothing going from the ground (black) of the motorcycle battery to the roll bar.

In vehicles, the chassis is usually ground so any things, such as your roll bar, would be electrically connected to chassis ground when they were fastened.