Help with boot solenoid - Ive been through 2 solenoids already...

I cant get this boot lock to work, Im getting good current to the solenoid and my earth is secure, I just cant get one powerful enough to work…

Starting to get pi55ed off at this stage spending too much time and money on these solenoids that are not up to the job. Ive replaced the spring in the boot lock for a lighter one, Ive removed the bushing on the lock to reduce the pressure and Ive tried fitting these solenoids many different ways with many different cable setups but they simply dont have the power to pull the lock, the last one I got claimed 8.7KGs of force but I seriously doubt its doing this.

Im getting a spring balance at the weekend to determine the force required but I would categorically say 8kgs would be more than enough considering my 6yr old can pop it from the inside with her small fingers…

What are those lever type solenoids I see people with? they appear to have a metal bar rather that this mickey mouse cable pull nonsense?  

Has anyone used an electric actuator on this?

Something like this?

http://www.ebay.com/itm/Multi-function-Linear-Actuator-Motor-DC-12V-50mm-Stroke-Heavy-Duty-1500N-330lbs-/271832670250?pt=LH_DefaultDomain_0&hash=item3f4a7d602a