rbonner,
I'd start looking for a bared section of wire in the outer plastic coated insulation anywhere along the length of the wire, but mainly in the electrical loom under the tank where it meets up with the relay, then work your way down to either of the two sensor/switches.
Remember, these sensor/switches are negative/ground activated, you might have a bared wire shorting on the frame, the bared wire could have, over time rubbed the paint off the frame in that particular region, therefore exposing the metal underneath, just enough to get a reasonable enough contact to short out and complete the circuit.
From memory, the wire colours are solid yellow for the 97c sensor/switch and white with a green stripe for the 110c sensor/switch (one wire per sensor/switch only).
An easy way to check without pulling apart the loom, is to disconnect the wire from the 97c sensor/switch and where it connects to the relay, the wire should theoretically now be electrically inert. Using a test light/probe connect the aligator clip to positive on the battery and touch either end of the wire on the connectors (after making sure the opposite end you are testing is adequately insulated first), if the test light/probe lights up, you've got a short, then you'll have to look to find the short, but if it doesn't light up, you haven't.
Repeat the same procedure with the 110c sensor/switch wire, if either one doesn't light up, your wiring is ok, it's then time to benchtest the relay or benchtest the resistance of the individual sensors themselves, by the workshop manual's, acceptable parameter COLD ohm ratings with a multimeter (set on 200 ohms or the "Omega" symbol) if you get 0.00 on the multimeter, the sensor/switch being tested has gone closed circuit and it is unserviceable (dead) if the multimeter says 1, it is has gone open circuit and that means it's unserviceable (dead) too.
If on the other hand, you get some numbers appear on the multimeter, match them against the ohm ratings in the manual, this number is the sensors resistance and if the numbers are within the acceptable range stated in the manual, the sensor/switch is working within the accepted functional parameters.
Mick.
