Simplicity

Okay the jumper needs removing as the seat switch connector already has a built in to prevent you from doing this. Besides this a grounding circuit and not meant to have +12v on it (I assume this what you mean by hot wire). Applying 12V is a good way to fry the magneto. If you remove the connector from will do the same thing as putting a jumper across the terminals.
 
Also it sounds like he has it where it is starting without depressing the brake/clutch pedal. If so he has it wired brake/clutch backwards. This switch is meant to break the ground circuit for the magneto when depressed even when there is no operator on the seat. The brake/clutch is a NC/NO switch with the NC side on the magneto kill and NO on starter circuit. The seat is a NC switch which grounds the magneto via the brake/clutch NC side of the switch when the pedal is up when the operator is off the seat.
 
Have the tech or yourself download the wiring schematic from Simplicity for you 1694016 and make sure to use the correct diagram as the there several in the manual.
 

kfoot
he put a piece of wire in the seat so it would still stay running when he got off the seat. but then he would put it in drive and release the brake it would die.

Then it is doing exactly what the OEM intend it to do if you attempt to bypass the seat switch.

He needed to charge the battery and get off the seat while starting to jump it. is the only reason he put a piece of wire under the seat. right now still can't let go of the brake with out it dying.

The seat connector can't be simply unpluged from the seat switch nor can you place a jumper across as both with act as if you are off the seat causing the mower to shut down as you let the brake off.
 
Remove the jumper, reconnect the seat switch, then install a fully charged battery. The dying problem will go away; unless, he has already screwed up the connector or has a bad seat switch.

Nor will it shut down if the deck is engaged. Both of these shut downs will nor occur should operator get knock off the mower so there is a will possibility of serious operator injury or mower might go out into traffic by itself causing someone else to unnecessarily hurt.
 
As I said there was no real problem as the short was intentional if you unplugged the seat switch. The problem was you wanted to defeat safety system so you could operate the mower unsafely and apparently someone was too lazy to set the brake in park position before getting off the mower; although, if the deck it would have still killed the engine; now it will not. Yet another unsafe operation if on unlevel ground as mower could roll away with the deck in operation.
 
IN my area we done had one child ran by mower with the deck operation while the owner was backing up. That kid is 6 ft under now.
 
And couple years ago me and another nearly kill a mower operator that was wearing headphones when she ran out into highway to make a U-turn she never even knew we were there even with blowing our horns. I waited till she came back and I stop her to tell her how lucky she was as we barely miss her as both drivers were traveling @45 mhp meeting each other. The skid marks made an impression on her. I have seen a couple times since and no headphones.