Solved.
After taking out the starter engine and disassembling it, I have seen that the fork of the coupling lever between the relay and the pinion, had opened unleashed from the ring of the axis of the pinion on which it acts.; When he was free, he had moved to the induced blocking it and short circuiting the engine.
Once the fork is adjusted and clean and greased the rest of the starter engine I have mounted and works well. I don't know if it will last another fifteen years, but thanks to your advice I am sure I have Ibiza for a while.
By the way, it has served as a guide to mount and disassemble the starter engine, the SEAT 127 workshop manual that is hung on this page. That the SEAT mounted the same engines in a lot of car models has come well, and that there are people who share those manuals for free even better.
Thanks again for your help.