Diesel witness flashes and costs to start

Hello everyone, please someone can help me have already happened to me several times that the diesel preheating witness starts starting to flash and it is hard to start by releasing a white smoke. Once it has been started continues to flash until it passes about fifteen minutes stop flashing. I have taken it to the workshop and they have fixed it several times, but it has lasted 10 months and has occurred again. They told me in the workshop that is something of the fuse box.

Does anyone know what can be? Will it be a relay?

Please I need help.

Greetings. Thank you.