67 Ignition issues

[jerrya59]

Bought a 1967 K10, at times when starting the starter just clicks about 5 to 10 times before it engages. Doesn't do it all the time, sometimes it starts right up. I have replaced the starter and the ignition switch still have the issue. Had a technician tell me that at times there is only 6 amps going to the starter which he says is not enough to engage the starter. He looked at the connection at the firewall and it worked every time for about a month than back to the intermitting issue. Could the ignition switch be the issue if it is not a 67 only switch? The switch from the previous owners had a accessory position and I replaced it with the same. Is the only difference with the 67 switch the accessory position? Any help with this would be appreciated.
Thanks