Police have said 205 cars were hit by car stereo thefts in Cardiff over the weekend - four times the usual number.
Theft warnings have been sent Neighbourhood Watch groups
Reports showed 95% of them were Ford models. The car firm believe this is in light of an "urban myth" that they can be used to decode digital TV boxes.
Police confirmed the rumour but officers have spoken to Ford and the digibox manufacturers who said there was no link.
Ford told BBC News that components cannot be used in this way.
A spokesman said it was "pure myth" sparked by an off-the-cuff comment from someone within the motor industry.
Meanwhile, police in Cardiff have issued a warning after a "substantial" rise in car crime over the last week, with vehicles in the Fairwater, Llanishen and Llanedeyrn areas being particularly badly hit.
Ford spokesman Paul Wilson said: "We have spoken to our radio manufacturers and this week we have been in discussions with digital box manufacturers. and I can categorically state that there is no component in the radios that is compatible with the digital boxes.
"This sort of urban myth is not doing us any particular favours or the car owners.
"There is no truth in the rumour whatsoever."
South Wales Police this week issued a warning to car owners living in the city.
Graham Lawrence's taxi was a target over the weekend
In a message to Neighbourhood Watch and community groups, they said: "Over the last week there has been a substantial increase in car crime. Many of these offences have taken place during the hours of darkness.
"Residents are urged to park under a street light wherever possible and to remove all objects including radio and stereo systems fascias.
"At the present time car CD systems are a particular problem, removal of the facia renders them useless to the thief.
"It has been noted that at the current time Ford vehicles are particularly being targeted."
Mr Wilson from Ford added: "We would urge customers to make sure the security panel of their stereo is removed from the radio when the car isn't in use and to make sure they take the security panel out of the car, not leave it in the glove box."