We have a 2011 Case Steiger 400 that is pulling a 2011 JD 1770NT 24 row 30" planter with CCS, XP units, pro hoppers and SeedStarXP. The controlling monitor is a 2630. Behind the planter we're pulling a 2011 JD 1910 air cart. The controlling monitor for it is a JD 2600. Both units are provided position information via a NMEA string from a Leica auto-steer system. Both systems are receiving a simulated radar speed from a SkyTracker "hockey puck" GPS unit (one unit tied in to both harnesses). I have been struggling with low supply voltage to the electronic power modules on the planter ever since we switched to a red tractor and it makes life miserable in the field. I want to get to the bottom of it. Since I believe the problem could be from any number of harnesses, I'm going to make several small questions in separate threads. This paragraph (in blue) will be the same in all of the threads so if you read more than one part, feel free to skip the blue part next time.

First of all, I want to focus on the JD tractor harnesses themselves.

1. Why do they need a radar (simulated or otherwise) input to be able to work? The display knows position from the NMEA string so why can't it get speed from the NMEA string as well? I understand that if my GPS fails I'm not going to be able to plant if there is not another speed source, but I've got enough that depends on GPS that I won't be able to plant anyway so I would at least like the option of being able to get speed from the NMEA string rather than the radar input on the harness. Is there any way to do that?

2. Since I have two JD tractor harnesses in the cab (one for the 2630 controlling the planter and one for the 2600 controlling the air cart) I have an incredibly huge wad of wires lying on the floor next to me. I shudder every time I look at it. It appears many parts of it are not use. One that clearly comes to mind right now is the port for plugging a Starfire receiver in. Since I don't have one, I don't use that. Can you get simplified cables to reduce the huge wad of wires? Can you get a pinout of the cable and remove the parts that you don't want? Can I shorten said cable so that the installation is neater? I would love to do that as a winter project because it's a really embarrassing big mess which also makes diagnostic work more difficult.

3. How much power for the planter comes through that harness rather than through the 7 pin connector or other harnesses? I keep getting an error that goes something like "check voltage between pins (something, can't remember) and 3 on the 9 pin connector". Is that the tractor harness or is that some auxiliary power harness or what?

Just any specific knowledge at all on John Deere tractor harnesses would be very much appreciated here. Thanks.