I want to make a mod that allows me to click on dead bodies and chests or whatever whilst on my horse so I don't have to get off it all the time.

I already have an auto harvest mod for ingredients, but I need to access dead bodies from my horse too.

The problem is not the distance, but the fact that the same control is used to open the dead body inventory and to dismount.
I have no idea how to work around this one,

Any way, the setting that controls the activate distance is http://cs.elderscrolls.com/constwiki/index.php/IActivatePickLength

The control to dismount does not make you dismount if an activatable object is in the players crosshair and the Activate display pops up. I collect ingredients from the taller plants from horseback with no problem.

So, changing the distance should help do what you want.

Thanks guys, made it work so I can select plants and bodies etc that are on the ground from my horse.

Would be better to be able to toggle it on and off when I'm on or not off my horse, as having a longer reach when walking feels a little weird, but there you go.

You could make a little quest script to set that value to the higher one while you're mounted, and back to normal when you're not, maybe?

Good to know you can activate thing from horseback.
I think i had trouble doing it when sitting on a chair.

Yeah I've thought of doing this, it requires OBSE which I don't currently use but probably will soon, I might even install it today.

Also, its says ont the wiki that Gameplay Settings always revert back on save reloads, which means I'd have to figure out how to do that with OBSE, which I've no experience of yet.

You're looking for http://cs.elderscrolls.com/constwiki/index.php/GetGameLoaded - set the settings in there and you're off and running.