OK got the wires in, time for the PCA9685 servo driver.
Printed out a small carrier that fits snugly in the gap and hold the board nicely.
Used the 16 way as follows.
1) 3.3V from Raspberry Pi 3 (control logic)
4) OE (Not used yet, but tie it to ground and the output will stop)
5) Logic Ground
6 & 7) V+ power for the bicep rotate servo
8) Signal for the bicep rotate servo
9 & 10) Ground for the bicep rotate servo
11, 12 & 13) V+ from battery isolator switch
14, 15 & 16) Ground from battery supply.
I did try to install a small SMPS buck converter with the idea of switching to a 12V SLA battery instead of the 6V SLA I'm using, but it wasn't big enough or had too much voltage drop, so i removed it.
We don't know if we don't try….