What can cause the engine fuse to blow when I turn the key on? Soon as I turn it on and the check engine light pops on the fuse pops. The check engine light has always been on and stays on. Last night coming home from work I stop at the store and cut it off but when I went to start it it wouldn't start just turn over. Looked at the fuse and seen it was pop replace it and that one pop so I got under the truck looking to see if I seen any wires having bad places in them and nothing but found the 4wd wire unplugged on the hog head on the front. I plugged it back up and it fired up. Ran fine durning the day today but when it got dark its when it started. I went back under the truck and everything is still plugged up and all but I do t understand y it just keeps doing this. Any idea?