If you have a sw bridging 15 and 87 @ the relay , then speed sensors , pressure limit cut-out, temp cut-out, etc. circuits are all out of the circuit b/c that jumper is direct 12v from fuse F/7 to clutch and by-passes all sensor inputs to relay.
So, if the clutch is dropping , you have a poor contact at fuse 7 or a bad upstream feed to that fuse, or a bad clutch/gap.
The test would be to put a test lamp at 15 and ground and see if that goes out when clutch goes out. IF YES, that would indicate fuse/feed upstream problem..
If NO, that would indicate downstream problem....clutch/coil/wiring..

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A Dalton