Make sure it is of sufficient guage to handle your radio's power consumption and that the shielding has a good, strong connection to ground on the vehicle chassis or frame. Of course, the best performance can be obtained from a more expensive radio with better noise suppression circuits. These measures, however, will improve the engine noise levels for nearly any mobile radio. Engine management systems can also cause interference because of their high switching rates in digital logic. However, engine management systems are also very susceptable to interference from radio transmitters but rarely fail to operate properly as a result.
Avionic systems are very sensetive.
I've got a good one for you. A friend of mine had a CB in his car and whenever he keyed it the anti-lock brakes started to pulse.