77 Chevy P20 Step Van NO CRANK???

I posted this in GMC forum, but hopefully someone can help me here. I have a 77 Chevrolet P20 step van with a 5.7L. Recently, the original problem that arose was that the truck would have to be jumped to start. Even after running for an hour. As soon as you shut it off, it would either crank very slow or not at all....just the bendex extending from the starter. I removed the starter, battery, and alternator, and had them all bench tested at AuZo. All three tested good. The battery is a new replacement, and the alternator is a new rebuild.

Now the bendex extends, I have all lights and power where it should be, except the gauges, haven't gotten those sorted yet. But there is absolutely NO rotation or crank to the motor. I thought it may be vapor locked or something similar(?) so I now have all the plugs removed and STILL no crank at all, but the starter bendex extends, and I can rotate the motor at the flywheel..

So I dig in and try to find whats going on. I've found several hack jobs in the wiring harnesses and wires going everywhere. Ive cleaned up the harnesses and have tried to pinpoint my problem. The distributor was loose enough to turn easily by hand, but I was able to set the timing (for now by ear, engine response at idle and high rpm until I can rent a timing light and do it properly), I replaced the starter solenoid that's mounted to the firewall, ad damn near scratched a hole in my head trying to figure it out. Could the ignition switch or ign switch wire to distributor cause this?

I'm going out now to check the neutral safety switch, wiring to distributor(again), and fuse block(again). The only other thing I can think of to check now is my grounds or a fusible link may be bad somewhere.

Any help will be appreciated. Thanks. Sy

If the bendix clicks in but the starter doesn't turn the engine over, look at the grounds and also look at the gauge of the wire going to the starter from the battery. It must be 4 gauge or larger, and if it's a fairly long run, make it 2 gauge. Make sure the cable from the negative post on the battery is also 2 or 4 gauge and is directly bolted to the engine.

It appears that the starter isn't receiving enough current.

Try this: Turn the headlights on. Turn the key to crank. If the headlights go out you have issues with the batt cables, connection, etc. If they stay on bright you have issues with the ign sw or the wiring from there to the starter.

Let us know what you find.