Starting and wiring issue

[72longbed]

To start off with my truck is a 72 with a 390/auto. It has the full Mallory unilite setup with promaster coil, ballast resistor, and noise suppresor. No matter how long I crank it, it will not start until I release the key. Also on occation (like 1 out of every 15 starts) it will not fire and when I relese the key and I get a hiss through the carb and the motor will spin backwards for a second. I have the mallory wired like this.. 12v switched wire from the cab (old radio wire) to the ballast resistor, then another wire coming from the other side of the ballast to the + on the coil. I didn't use the resitor wire from the factory (its cut and capped right where it comes through the firewall) I have changed the starter solenoid and the ignition switch which did no good . I know it has to do with the wiring in the starting circuit because it runs perfect once started. Sorry for the long and double post and any help will be greatly appreciated.

[fordman]

oh ok i see you used the radio wire whichis only hot after the key is let off. try a different source for the power to the resistor. that should let it start and stay running .

[72longbed]

Cool thanks. I guess I never thought to test it when it was cranking to see if it stayed hot . any suggestions on a good source to tap into?

[Thunderfoot]

The only wires that are hot when cranking are; the ignition wire, the wire to the starter solenoid and the exciter wire to the alternator, everything else is cut off during cranking... There is a wire from the starter solenoid to the coil (Brown) that is used during cranking to give the coil full 12V for cold starts and is activated the same time as the starter. You may be able to keep it running with this hooked back up as the short time between start and run on the ignition switch it might not see.
The best way would be to cut the old ignition wire at the ignition switch and splice in your new wire there.

[willowbilly3]

You may need to run a wire from the other small terminal on the solenoid to the coil + That will also bypass the resistor and give you full battery voltage to the coil during crankiong.

[72longbed]

Ok guys thanks for the replies. I ran my wire off the ignition switch of the red-green stripe wire and all is good now, fires up instantly. Thanks again