IR has used a HV (High voltage) connector to supply power from the leading locomotive to the trailing locomotive. This is a 25KV High voltage connector. I've highlighted the connector in the attached image (Credits: Suarabh Raut - Youtube link - click here
In addition, the control signals are transferred through the I-V connectors. Even during regenerative braking, the same HV connector transfers the power from the trailing loco to the leading loco's pantograph and further to the OHE cable.
Normally even if two...
more... locos are MU-ed, both locos need to have their pantographs raised to get power from the OHE. But in case of the Twin WAP5's, since they are supposed to run at high speeds, two raised pantographs might result in uncontrolled OHE oscillations. So to avoid that, IR is using the HV connector to avoid the need to raise both pantographs.