If you go with an aftermarket option for rear remotes there are a plethora of options and mine has OEM remotes so this is related to OEM. Will leave any discussion of A/M to others who have them or more expertise with them. The below is a L4701. I believe the L3901 is similar but probably a good idea to confirm with dealer.
Now that disclaimer is done…
Regardless of rear remotes, beside and slightly below your right hip as you sit in the seat there’s a rather large lever that controls the 3 point. Just above and behind that there are slots. Without OEM remotes there’s nothing in the slots.
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With OEM rear remotes, there are one, two, or three hydraulic valves mounted on under the right side of the seat. In this case, one is larger than the others because it has a float detent whereas the other two are center returns. The first one (closest to center of the machine) has to be a center return due to insufficient space for a float or continuous flow detent. The second and third can be detents if you wish.
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The controls for those valves fit in the three slots above the three point height control. All three control levers are different heights so you can reach down and easily tell which one your on by feel without looking.
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The actual remote connects are stacked on a bracket on the right side of the ROPS. In my case, they almost always control the hydraulic top link and side link with one left over. I normally have the float detent valve hooked to the top link but can float the side link by swapping the hoses at the quick connects. I prefer ability to float the top for mowing and prefer to float the tilt for pulling gravel out of ditches.
I don’t currently have a specific use for the third remote. I had it installed at the same time as the other two because a significant element of cost is labor due to having to remove and reinstall the right rear wheel and fender for access. At some point if I get ambitious I may add a hydraulic cylinder to my manually adjustable back blade and if that ever happens I’ll be needing the third remote as I’m not giving up the hydraulic top and tilt for grading work.
Edit: Since someone else mentioned cost if the OEM remotes, mine were dealer installed for $3200 but that also included the hydraulic top link, hydraulic side link and additional hoses and fitting associated with the cylinders. They ain’t cheap. Installation was very easy for me because I dropped it at the dealer one morning and picked it up the next afternoon. Biggest issue for me doing it by myself, in my mind anyway, was removing the 600+lb loaded rear wheel/tire assy. I had access to an appropriate tire handler but it was 2 hours away so I’d have 8 hours in the two round trips just to pick it up and return it. I’m not retired so dealer was a better option for me.