My 88 deville has cruse that won't engage. Also the "service soon" light is on.

I had the car serviced, by cadillac, and was advised that whenever the service light was on the cruse control was shut dowm. there was an error code #21 TPI sensor.

I did not have it fixed because I don't understand why a service light can't be reset.

The car runs like new, has 141000 miles and gets 21 mpg. I don't need cruse, should I worry about it.

Where is a good source for minor cosmetit parts, like the emblem in the middle of the spoke wheels and a DeVille emblem for thr glove box

Any advice? David