Fuses and electrical problem

This is what i'm looking at. The red wire plugged into the battery circuit is running to the black can? Id don't know what the black can is. Looking at the Haynes typical for this year and can't find it. It looks like it was put there aftermarket. Each side has two wires. One side is one black and one red. Other side is one orange and one black. Switch wires look good on transmission. The orange and black side of black cylinder turns into another black and red which ends i'm n a three hole male plug. I'm lost as to what it is. Maybe something with towing? I forgot to mention. There are three towing options installed in the truck, travel trailer, fifth wheel and regular pull behind trailer.

I have already disconnected the trailer brake control. It had no power and was in the way to where we are so far.

Is there a way to test the ECM? When I put the obd1 it just kept flashing 9 over and over. I waited a good ten minutes to see if it would change but it didn't.

I just recently stepped into this truck blind few weeks ago it does run. I didn't realize that a lot of the electrical had been Frankenstein. I'm slowly working my way through the vehicle trying to remedy one problem at a time.
I was just hoping that the ECM could tell me something other than code nine maybe lead me in a direction to get things fixed and running as they should or installed as I should say as they should be. What was weird is whenever I grounded the test where the OBD1 plugs in. It never flashed code 12 letting me know that the system was functioning properly. I was under the impression at all OBD1 codes are double-digit so it caught me off-guard whenever it through just nine over and over again. I got to 30 amp circuit breakers and plug them in to the fuse panel only to find out there's no power running through the circuit breaker slots, like I said it's a Frankenstein mess and I don't know or even understand what how or why it's like this. I feel as if I'm trying to piece together a puzzle upside down with no way to see the picture the Haynes book has saved my life so far along with your help letting me know where certain things are that are not listed in this book I really appreciate you taking your time with me I just need to get this vehicle up to par so I can drive across America in it back to the East Coast. I'm going to pull the negative lead off the battery so that I can pull the fuse box through and see what the back of it actually looks like. It just doesn't make sense to me as to why there isn't power run to this and how that the vehicle could still properly function.