If I have ringworm of the body. If I cover it, is it a bad idea to have sex?

Yes. Ringworm is caused by a dermatophyte (a fungus which infects the skin). It is easily transmissible by direct contact, and, at least in my humble experience, it is not possible to have sex without exposing areas of the skin, you will be likely to be infecting your partner. Wait until it has cleared up.