The Heart of Gold was somewhat less than 100%. The service had been useful, as the neutramatic machine would now deliver a damn near perfect cup of Earl Grey, but the mechanics hadn't exactly been thorough. All the standard points of the service manual had been covered, but then the service manual didn't cover the possibility of the owner deliberately pulling a few wires. So, behind an innocent looking inspection panel, the wires (which Zaphod incorrectly assumed had belonged to the 'fasten your seat belts' light) remained pulled. They were actually part of the microprocessor controlled reverse interlock relay memory bank of the infinite improbability drive. This device dumped all the necessary co-ordinates of the Universe into the ship's computer for processing. This enabled the ship to assess current location against potential and possible location, in relation to requested location. The ship's computer would then arrive in the requested location and dump all these details back with the co-ordinates of the ship's latest position. This meant that next time infinite improbability was used, the computer couldn't update the current location in relation to it's position in the Universe, as, unfortunately, this information would normally travel back through one of the pulled wires.
In layman's terms, the next time infinite improbability drive was used, the ship would arrive totally lost and unable to use infinite improbability drive until the wire was replaced and the co-ordinates reprogrammed.