Servo PWM to H-Bridge (High Current)

Hi all, as some of you might remember I was having a problem with my survey boat zig zagging terribly while carrying out a mission.  At first I thought it was a Mission Planner parameter setting, but it turned out to be the little L298N H-Bridge failing due to excessive heat.  This was caused by me upgrading the outboard motor to a Suzuki 2.5hp four stroke which turns out to have a LOT more drag on the pivot (steering) column.  This drag put extra stress on the little 2A H-Bridge causing it to fail intermittently. 

The solution was to upgrade the H-Bridge to a 10A H-Bridge, but being in South Africa, none are available locally so I built my own from this diagram - 


Unfortunately when I connect it to my PWM output from an old rc servo motor, it appears to go into a DEAD SHORT.  Clearly I am doing something wrong here.

Can somebody please help me here.

Here is my setup - 


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