First off, I have over 70 years hands on experience in electronics. Military, Industrial and Civilian. Like to think I know something about troubleshooting.
I have three, 70 bulb multicolor light strings all with the same problem!
Actually each 70 bulb string consists of 2, 35 bulb strings wired in series, and those 2 sub strings wired in Parallel giving the 70.
The colors repeat every sixth bulb.
On all three strings the first bulb from the plug is out! However if you remove it from the socket 34 more bulbs go out. So current is definitely flowing through the first bulb.
If you exchange bulbs 1 and 6, the problem remains with the #1 socket and the previous #1 bulb works fine in position 6.
I've also checked across the #1 socket with an ohmmeter set on it's highest range for any indication of leakage. NONE!
It would seem the problem is with that first socket but I find none.
Ideas? Please make me feel stupid!