These machines are very sensitive to low battery voltage so be sure your main battery is good first. If running remote via wire the unit should be charging the remote. Light on far left is indicating charge for remote (from main battery/rectifier). If showing green light then battery is being charged. If showing red then remote is NOT getting power through the cord. Next light is relative to communication with main board on unit. If green then remote is talking to the unit. If red then they are not communicating. Issues could be main board, cord, or remote (among others). In my experience the trouble usually lies in the cord which is the cheapest to repair (Last time I bought one it was around $300). If you need controller repairs try Carolina Electronics (only place I've found to make repairs to electronics on these units). One of the bigger issues I have with starting mine is relative to the oil pressure sending unit. It (and the connector I will refer to below) can be found on the passenger side of the engine (look for the oil filter). When it's cold out we have to by-pass the sending unit (un-plug the connector and run a jumper wire from one side to the otheror the 2-pole connector) to get the starter to engage. Once started then remove the jumper and plug it back in. Yesterday the sending unit ground wire broke off of the ring connector where it bolts to the engine. We replaced it today but we were able to simply hold the wire against ground to get it to start before we repaired it. Once started the sending unit won't stop the machine from running but it does keep the starter relay from engaging. That is another thing to check. There are (2) relays under the hood and you may want to check those as well. By the way parts on the old 820s (metal body units) can be hard to find. You may want to buy a spare/parts unit if you come across one. Voltage regulator, or rectifier (I'm not sure which it is) can be problematic. I don't recall if on the driver or passenger side of the engine compartment but it is bolted to the cover on the side. Be sure to turn off (BOTH) the switch on the remote, AND the key when you shut the machine off. Otherwise you run the risk of draining the battery.
Over-all these are great compactors. I've had mine since '04 (bought with about 400 hours on it) and it now has about 2,800 hours on it. It takes a beating but has been pretty reliable. Be sure to change the oil in the exciters right away. Mine grenaded right after I bought it but I have not had any exciter/bearing issues since it was rebuilt. While you have the drums off be sure to put some extra hose guards on the hoses that operate the drive motors and exciters. Eventually they will rub through and it's a PIA to fix them. I also recommend that you keep an eye on the latches of the engine compartment side doors. They can vibrate themselves off. If you employ a lock on the controller compartment/dashboard lid be sure to keep the hasp closed (or in the locked position) when operating the machine. If you don't the vibration will start to "erode" the hasp of the lock until it simply breaks (yes, it vibrates that much).
These things remind me of R2D2. "R2D2" all the way!