Pin one on P702 is to the left and on the lower row of pins as you look at the Magni from the front.
One of the things we are doing on rev 5.2 MCB is having a larger white dot that is not under the connector. You can see pin 1 on P702 will be the only pin with a square pad on pin 1 hole.
Please also see our detailed pinout document that shows what I just explained above: https://learn.ubiquityrobotics.com/Magni_MCB_pinout.pdf
Even if you look at all the pins and so on please please get a meter that will buzz when you touch the probes together and make sure the pins you think are ground get connected by testing with the buzz.
Unless you are extremely familiear with dual row ribbon cable connectors it is very very easy to make a mistake because P701 has no ‘key’ because it is an odd 20mm high dual row connector it is designed to have the raspberry Pi plug in and does not have a key to ensure proper ribbon cable use on that end.
Also the rev 5.2 boards will have extra electronic circuit breaker to protect the high current battery connection going in the P702 connector at 24V as another improvement.
I am telling you these improvements so you realize we are always trying to learn from field problems and make improvements so future product shipments are better.