914 no power to yellow wire in starter solenoid

[cabmandone]

Trying to help my B.I.L get his car going. We made a jumper to the yellow wire terminal for the starter and engine cranks. There is no power at the yellow wire for the starter solenoid. Is there a relay in this circuit or is it a straight wire from the key switch back to the starter solenoid? We have verified grounds but when the key is turned to the start position, we lose all power. With the hot wire jumper to the solenoid the engine will crank. We need to find out where exactly the yellow wire to the solenoid gets power. Any help would be appreciated!

[cabmandone]

FWIW, ended up that a connection in the tunnel (yellow-red and yellow) came loose killing power to the starter solenoid.