"Engine" fuse keeps blowing

My customer has a '97 Escort that has had an apparently leaky heater core. Now, the car won't run more than a few seconds w/o blowing the "Engine" fuse. Any liklies ? Or is this going to be the proverbial needle in a needle stack electrical problem ?
Thanks in advance for your time, 2spot, over & out.

you defantly have a short to ground somewhere. what i would do is get a headlight put 2 leads off of it and set it up on the dash where u can see it and plug it in to each side of the fuse holder turn the key on the light should light up and then go and start shaking small sections of wiring harness to see if you have a short to ground that will get you in the genaral direction