[strictlypersonl]

*Note... I'm going to have to check the logic below before you do anything. I'm worried about inadvertent feedback...

This might work, and it will save having to run a wire through the firewall:

Connect one side of the light to a switched power source. (i.e. piggy-backed on one of the green-wire connections at the fuel gauge or tachometer.

Connect (piggyback) the other side of the light to the fan override switch terminal with the blue wire.

(This will only work if the thermo-switch will absorb the extra current from the bulb. If if can't, the automatic function of the fan will no longer work, and you'll have to run a wire to the fan relay power side and ground the other side of the bulb.)