Audio Systems: AM reception, spark plug wires, antenna cable

Question
I have a 94 GMC truck, with an Alpine aftermarket stereo. My FM reception is fine, but AM reception is poor. Although with the engine off, the AM reception is much better. Any help would be great, thank you.

Answer
Dave,
Several noise sources are present in most vehicles that will effect the AM radio reception. For starters, the engine computer and spark plug wires, the fuel pump and other DC motors etc. You may want to try installing a double shielded antenna cable/wire. Also you can try running a ground wire to the chassis of the radio itself to the fire wall. AM radio noise can be cut down some what by installing small ground (braided) wires from the fenders to the fire wall and from the hood to the fire wall. In extreme cases where the AM radio has to be used, you could try installing resistor spark plugs and resistor wires plus a complete shielded distibutor cap and wires. Lastly, completely isolating any noise that enters the radio through the power wires by using DC line filters.

TOM,
T&D ELECTRONICS
tdeser@zoominternet.net