Preheat lamp stays on after box installation

Hello, I installed a 'power box' in my G3 iZ, but the preheating light doesn't turn off when it's installed. When I remove it, the light turns off.
With the box attached, it starts poorly, and you can't really notice any improvement in performance.
Where could the problem be?

Thank you for any response.

Hello,

Either the device is defective, or it's simply poorly made or incorrectly configured.
If you're looking for a way to increase performance without causing excessive stress on the engine, and with the added benefit of increased safety, this might be something for you.
http://shop.dieselschrauber.de/product_info.php/products_id/77

Best regards, Rainer.