You have an "89" so it has the engine diagnostic computer in it, though somewhat basic, it can give you a general direction to start. Without a Bentley manual you will have to find another source to read the codes.

On occasion the check engine light can be activated by electrical abnormals, ruts in the roads, moisture in the fuse panel, or a verifiable serious mechanical problem. At your discretion, you can disconnect the neg bat cable for a few seconds to reset the check engine light. If you have a verifiable problem, it will re-activate the warning light when restarting the engine. However, should you have a serious mechanical problem it may also compound your situation. Usually best to check out the code first.