WING BODY OVERHEAT - B737 NG

[owl-attack]

Hello

I am not able to understand a few things written in the MRG book on 737 (by Pat Boone) and B737 Technical guide by Chris Brady

MRG says:

For a wing body overheat, the leak can be confirmed on the bleed air duct pressure indicator.
What does the book mean by this, What indications am i supposed to see on the bleed air duct pressure indicator if there is wing body overheat. All I know is that once the NNC is followed and respective side bleed and pack switches are selected to OFF position, the BLEED AIR DUCT PRESSURE pointer for that will drop to zero . So what does he mean by a leak can be confirmed on the bleed air duct pressure indicator?

Boeing 737 technical guide says (Chris Brady):

Wing body overheat light on the left side is more critical , because this includes ducting to the APU.

How does leak on left side make it any more serious than right side. Am I correct to say that it is more serious because of more ducting than right thus more chances of airframe damage?

Last question w.r.t the QRH:
The WING BODY OVERHEAT NNC, tells the crew to switch off the TRIM AIR switch if the wing body ovht light stays illuminated after switching all the bleed sources. How will switching off the TRIM AIR switch help?

Kindly help me with this confusion

Thanks