I have a 1990 isuzu 2.6L engine pickup that I recently purchased. The check engine light stays on constantly and I researched on how to find out what codes are being stored. When I found where I use a jumper wire to check them, there was already a jumper wire there. I removed the wire but my truck would not turn over without it being installed permanently. Is there a specific reason that someone may have done this for? I appreciate any help in advance.