I have a 68 400 conv. that I recently had the motor gone through. I have it in the car and have been trying to get it started. It only wants to run while I am turning the ignition on. As soon as I let go of the key, it shuts off. What could be the problem? Any ideas or even comments will be appreciated.

Thanks

It would seem like a problem at the ignition switch or fuse to me. If a wire has come off the switch or something, this could happen so I would check that out along with the fuse. Or, the switch could be bad. From the wiring diagram in the 68 service manual it appears that the pink wire to the switch should make the circuit when the car is running. With the key in the "run" position, there should be voltage on this pink wire. Some others here likely have experience with this.

Dave

I had a problem like that many years ago after putting an engine in a GTO. The alternator wasn't connected properly. Check your wiring.

dvrmarch is correct.
The original wiring has 2 wires going to the +coil. One (yellow) comes up from the starter solenoid to provide 12v during 'start'.
The other (pink/black) comes from the fusebox thru the harness to provide reduced voltage during 'run'.
(my wires dont match those colors anymore.)

it looks like you have power to the coil during 'start', but no power to the coil during 'run'... likely due to faulty wiring, or possibly a bad ign. switch.

check the coil+ with a test light or voltmeter with the ign switch in 'run'. it should have power. if not, make sure the harness wire is connected and getting power.

here is the circuit from the ign switch to the coil:
http://www.1968firebird.org/68wir/68wir2.html
pink/black between coil+ and firewall plug K

http://www.1968firebird.org/68wir/68wir3.html
pink between firewall plug K and ign switch.

Let me add that the vehicle does have its org. wires with the correct colors. Also the vehicle was converted to HEI prior to me obtaining it and the pink wire runs to the Dist. with the yellow wire comgin from the dist. to the starter. with the purple wire running from the ign. to the starter. Does that seem right?

are the yellow and pink both running to the BATT terminal on the cap?

Thanks all for the advise and ideas. The problem was two fold. Loose connections and a crank pully with the timming mark in the wrong plcae causing of course the #1 being off. Thanks again it now purrs like a kitten. (I mean TIGER)

Just wondering--What prompted you to inspect the crank pulley? Do different years pulleys have the marks in different places? Glad to hear you are rolling again.

Bruce