Looking for some Electrical/ECM help please!

I just bought a 1983 Firebird Convertible. The alternator was bad, so I just replaced that. My Check Engine light came on after driving the car for 20 miles. Got back home, checked the ECM IGN fuse under the dash-it was blown. Replaced the fuse and forgot about it. The next morning it started, and ran fine....Until 20 miles down the road when the check engine light came on again. Sure enough, the fuse was blown again. I've heard of fuel pumps going bad, causing it to pull more amps; I don't think this is the case. The car has the carbureted 305. I guess I'm confused why the fuse wouldn't blow (if there is a short) when I first start the car and drive it down the road but it only blows after I've driven about 20 miles....?

While driving down the road, I pulled the blown fuse out (10) and replaced with a hire one (25), but still blew right away.

Anyone have any ideas before I start looking for a needle in a hay stack, looking for a short in the wiring?

 

This is going to be one of those things you have to dig around for. Good things to check that are commonly wired wrong, do you have an electric fan added or an amp and aftermarket stereo? There is a brown wire going to the alternator and a blue wire going to the choke heater that are on that circuit. There are two places in the fuse panel on the bottom left that a wire can be added to add a protected circuit through the ign fuse. If either is used trace them down and see what is added on.
Here are links to the wiring in your car.
http://austinthirdgen.org/mkportal/m..._continued.gif
http://austinthirdgen.org/mkportal/m...ody_wiring.gif
http://austinthirdgen.org/mkportal/m...ine_wiring.gif

 

Thanks for the wiring schematics Joe Tag! This car seems to be unmolested for the most part; no aftermarket amp or subs, no electric fan added, just a cd player (cd player has its own fuse). Everything under the hood looks good also (not any wiring hack jobs that I have found). There is a wire coming from the fuse panel (the area you talked about where a wire can be added), so I will trace where that one leads to.

Looks like I'm going to have to do a lot of wire short hunting....

 

Found the short! A relay of some sort had fallen onto the exhaust manifold and melted to it, causing the short. It wasn't shorting right away cause once the manifold got hot enough, it would melt more of the plastic and cause the short.

So after taking a good look at the wiring under the hood, it looks like it has been hacked a little. It also looks like the wire (relay or something? see pic) was never really hooked up. I cut the relay off and black taped the wires. There are also other connectors and hoses that are not hooked up or have been capped off. I'm pretty sure its components that are for the EGR system. The car still runs great (relative for a stock 305) so I'm not too worried about it, but just was going to see what others can see from the pictures and have any advice on it.

Thanks!

 

some more pics

 

one more