The starter will engage once for less than one second, but then does nothing on subsequent cranking attempts. The test light goes out on all starter wires in the cranking position once the starter engages once. I am stumped. Can someone please help.

I have a fully charged battery, 12 volts from battery to switch, 12 volts into the purple wire going to the starter with key in the start position and 12 volts from the battery to the starter. All of this is prior to hooking up the starter. I have had the starter independently tested at advanced auto parts and it passed with no issues. I can see volts going to the + on the coil from the starter in the start and run positions, granted the test light is dimmed.

Check the negative sides of the circuits. Ensure you've got a good, clean, metal to metal contact on the negative battery cable to the engine block and the battery posts. Also check that the starter is tightly bolted on, again with clean contact surfaces (metal to metal - NO PAINT).

You've stated you have 12 volts. Is that real voltage reading, or a generic statement because your test light comes on? You should have a reading in the high 12's/low 13's sitting static.
(A test light will just show you've got voltage - not that your circuit will carry any current.... you could have just 1 strand of a wire connected and the test light will work.)

Working with a test light only. I will check with a true voltage meter. All of my grounds are good and starter has been tried bolted up and with a jumper cable from the casing to a solid ground with the same result.

I've had that experience several times; on multiple vehicles.

I bet you find the problem is a bad connection; probably at the battery but anywhere the wires join is a possibility. As I recall, most of the time this happened, it was with a top-post battery.

There is enough connection to power a voltmeter that draws "nothing" for amperage. Hit it with the instantaneous ~700 amps of the starter engaging; and it messes the bed.

First Guess: if you remove the battery cables from the battery, the posts will be black. A battery terminal brush will shine 'em up real nice; be sure to shine up the clamps, too.

DISASSEMBLE, CLEAN, TIGHTEN, and PROTECT each connection in the starting circuit, beginning at the battery posts and working toward the engine.

OK, I beleive I have found a problem, but maybe not the problem. From the positive wire on the battery there is a brown wire that connects to a junction block. Connected to the junction block there is a larger guage red wire and a orange wire that termiates into a black 20 guage wire. The orange wire was badly burned, almost in half. I have referred to the factory wiring diagram for a 69, which does not reflect the orange wire terminating into the black 20 guage wire. Does anyone know what this wire goes to? Should I just correct the burned portion of the wire and go on, or is ths a syptom of another problem somewhere else?

I have referred to the factory wiring diagram for a 69, which does not reflect the orange wire terminating into the black 20 guage wire. Does anyone know what this wire goes to? Should I just correct the burned portion of the wire and go on, or is ths a syptom of another problem somewhere else?

The orange wire is a fusible link for the amp gauge. Personally I would put a 5 amp fuse in place of the orange wire. The fusible link is there to protect the gauge. The amp gauge draws very little power. See here (http://www.madelectrical.com/catalog/fusible-link.shtml) for more info on fusible links

Now, need to find out why the reason the orange wire burned up. I would check your connections at the horn relay, junction block and battery. In a factory gauge car, if the connections are bad or open, power will try to route through the amp gauge, which its not intended to do. Clean the connections at the horn relay buss bar, make sure wires are tight. One of these 3 connections would be my first guess.

http://www.chevelles.com/showroom/data/500/medium/Horn_relay_with_text.JPG


Factory amp gauge wiring. The black and black w/white stripe have orange wire fusible links where they connect at junction block and main splice (pic doesn't show this). This pic also shows the other fusible links, be sure they are good and in place.
http://www.chevelles.com/showroom/data/500/Chevy_old_with_amp_gauge.jpg

Thank you for your helpfull reply undee70ss, I will check all of the wires and connections.