I recently had to replace the sensor on my Water Pressure Idiot Light. I've had a few people ask me how its wired up and since having a few cut hoses resulting in wavy heads, its become apparent just how good of an idea it is.
My idiot lights are mounted on the A pillar roll cage tube right in front of my face so even in the heat middle of the red mist, they're bound to catch my attention. They are a normal surface mount signal indicator wired up to a plain light relay under the dash. Simple enough wiring, but the important part is the relay is triggered off a ground.
Both sensors open and close a ground when the oil/water is up to appropriate pressure. When the pressure drops, the ground circuit closes and the light comes on. This means with just the ignition on and the engine not, the idiot light is on.
The most important part is the sensor and where it mounts. We all have different ways of getting oil pressure and water temp, but sometimes run out of places to put things. The Water Pressure Sensor I use is actually an oil pressure idiot light sensor off a VW or Audi. The part number 021919081B gets you a VW Dune Buggy or Vanagon style sensor and if you search the local parts stores for 1990 Audi 100 Oil Pressure Light Switch, your likely to find one local.
My Water pressure sensor is mounted in the third hole back top front of the block and under the J boot. There are three taps into the water cooling cavity on the block from front to back and I use them as:
1. DME Temp Sensor
2. Water Temp
3. Water Pressure
Ill add pics if I get time and there's interest.
