A heads up on this one. I had a malfunction  a few nights ago on a -300 a/c #2 t/r overhead light on at push back. After many ops check good I got it this one. 1st I was going to ring out the the switches for target far and near . After unlocking the t/r and cycling it I found that the Left and Right t/r halfs on the #2 engine opening good but when stowing I found the half’s to be not closing even. So this was tripping the light now It’s not the iso valve but the hyd system return fuse is bad it’s the one above aft heat exchanger. And make sure you have a 1 inch crow foot for the front fitting. And dont run the packs before you do this as your hand are in a tight spot hope this helps.     Thanks to Nick.

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