Thanks Elektrodrive and Billy B for your answers.

I have now an idea where to look. Probably the inductor coil. It's a big heavy part on the PCB.
The forklift truck rides on e area with stelcon plates on the ground. I can expect that the connection wire is broken.

Can one of you supply me with electronic (pricipal) drawings of this controller board?
What price must I expect when I buy this controller board?

regards
Piet Blom