help finding a short
 

First some backround. I purchased a 1975 911s Targa last fall and drove it about 500 miles before pulling the engine and performing all the recommended upgrades in Waynes book. The blinkers and high/low beam switch didnt work so I had a new lever put in by an auto electric shop which cured the problem. Other than that nothing was changed before pulling the engine. A few weeks ago I finished the project and put the engine back in the car. I'm really a novice when it comes to electrical problems. With everything hooked up I went to connect the negative to the battery and got a big spark. If I disconnect the wires to the alternator I can connect to the starter and it turns over fine. When I try to connect the red wire to the alternator with the groundstap allready attached I get a big spark. I'm sure I'm connecting to the right posts as I took pictures before I removed the wires during the teardown. I've had both the battery and the alternator tested and they both check out fine. I've tried disconnection the wiring harness from the voltage regulator and everything else located in that corner of the engine compartment and then trying to connect the red wire to the alternator. Still a big spark. I cleaned the groundstrap conections(engine to alternator, trans to frame) as well at the battery terminals well. If I need to look closer at the entire wiring harness is it possible without dropping the engine?
Any help would be greatly appreciated,
Thanks,

Jason

Is key on?

The key isn't on when I try to connect the red wire to the alternator.

Re-check the starter wiring?

I connected the red and large black wire to the larger terminal together. Or do you mean the actual internal wiring of the starter? When the starter was initially removed it was completely covered in gunk and I used a lot of degreaser on it to get it clean. When the wires on the alternator are disconnected I can turn the key and the starter turns over fine. Do I need to have the starter tested?

Thanks,

Jason

I meant the external wiring...sounds like it's something else.

Have you triple checked the alternator wiring?

D+ - blue
DF - black
D- - 2 browns
B+ - 2 reds

with a large spark as you mentioned their is an obvious load on the circuit try removing a fuse at a time ,this may help in locating the amp draw, by isolating each circuit.

I'll check the alternator wiring again and try removing one fuse at a time to isolate the problem tomorrow night. Should I just remove fuses that have a red wire going to them?
thanks,

Jason

I was going to suggest removing the fuses, but then I thought you might not want to recreate that arcing thing too many times. Nothing good happens to electrical components when 12VDC(+) is repeatedly shorted to ground, which is what creates the light show.

Use caution...or better yet, use a multimeter. Pull all the fuses and see if you get a 12VDC reading across the fuse holder. All the fuses are running 12VDC(+), so if you get a 12V reading, one side is shorted to ground. Sometimes on a good circuit you might get a reduced voltage reading, but not 12V.

On the photo I took before disasembly I can clearly see the connections for the blue, black, brown and red wires so I know I've got these right. I can't see the connection for my groundstrap in my photo. After all the wires are connected per my photo I have one terminal left with one of those insulated washers. This is the one I put the groundstrap on. Is this the right terminal for it?
I pulled the fuses and cheched for voltage across the fuseholders. I got a full 12v in the heated windshield fuse. Nothing in all the others. I left the fuse out , tried to connect the red wire to its post on the alternator with groudstrap attached as above and still got a large spark.

What should I do next?