Re: new harness installed and wont stay started in the run position
Are you running an HEI distributor?
If you are, your problem may be that you have the resistive wire going to the distributor which if I am not mistaken is only suppling 9 volts, not the 12 volts that HEI need. The old point style distributors used nine volts EXCEPT when starting when the wire running from the stater supplied twelve volts.
Anyway, just a possibility, IF you have a HEI distrib. and a new OEM type wiring harness.
Hope this helps,
W 2LG 3L 4P