Authorities said the Calixtine Code, a 12th-century pilgrims' guide, had been stolen from from the Cathedral of Santiago de Compostela in Galicia, thinkSpain reported.
The guide and other artifacts from the temple, including coins, were found in the electrician's garage, authorities said.
ThinkSpain said his wife and son have also been taken into custody on suspicion of aiding and abetting in the theft.
The electrician had been laid off when ecclesiastical authorities were forced to provide job contracts and pay tax and social security for all their employees.
The electrician claimed church authorities owe him at least the amount the document is worth -- more than $49,500 -- in unpaid fees for his work at the cathedral.
The manuscript disappeared a year ago.
Ramon Yzquierdo, the cathedral museum's director, has said he believed the theft was an inside job.
Poor security at the vault from which the manuscript was stolen has been cited in the theft.
The dean of the cathedral, Jose Maria Diaz, lost his job over the theft.
Diaz, who had been the cathedral's archive manager at the time of the theft, declined comment, citing "higher orders" and saying commenting "wouldn't do his health any good."