I recently replaced the entire cooling system of our 1999 2.0 which included the expansion tank. The latest tank (17107514964) is also for some X5s and has the magnetic float inside it for the coolant level sensor (the original Z3 tank doesn’t have this float). I decided to try to fit a low coolant level warning light so I bought a sensor (17137553919) and the connector plug (6113235999). Looking inside the under-bonnet fuse box I saw a blank space for a relay holder (61131389113) and a salmon red relay (12631742690). I bought both of these plus 4 relay holder wire connectors (61138377732).
I opened the fuse box and tapped into a “live to start & run” wire (lots in there) via a 3A inline fuse. From this fuse I ran a wire directly to relay housing contact 30 and another wire to one side of the sensor connector plug. From the other side of the connector plug I ran a wire to relay housing contact 86. From relay housing contact 85 I ran a wire to an earth point.
The wire from relay housing contact 87a (to the lamp) went into the cockpit through the fuse box and the main wiring loom and then along behind the centre console and up to the steering column where it went into a Tyco-AMP 2 pin connector to connect the relay wire (pin 1) and an earth wire (pin2) to a flying lead containing the lamp. For good measure I added a small buzzer in parallel in case the lamp burned out.
I originally intended to use one of the connector pins in either the white or blue socket at the back of the instrument panel to connect to the wire from 87a and use a lamp in one of the unused spaces in the instrument panel circuit board. I was unable to find a suitable pin and my pin-out arrangement didn’t seem to match the official wiring diagram so, rather than risk damaging the panel’s electronics, I decided to make the warning lamp independent of the wiring in the circuit board. I drilled a 4mm hole in the back of a spare 1.2W lamp holder and pushed out the bulb leaving the metal locking tabs in place (but not connected to anything) to lock the holder into the circuit board and then I fed a pre-wired 12V 5mm red LED down through the hole so that the LED sat where the bulb would have been. I used heat shrink over the wires to hold the LED firmly in place, clipped the LED into the circuit board and connected the wires from the LED to the Tyco-AMP, one to the relay wire and the other to the earth wire.
I was going to add a wiring diagram but I couldn’t get the post to accept my jpeg; if anyone is interested, PM me and I’ll email one
When the coolant level drops, the light illuminates (I used the unused “catalytic converter overheat” space in the display) and the buzzer sounds.
Does it work? - Yes, will it tell me if I lose coolant? - I hope so, but at least it kept me from getting bored for a few days!
UK forum for general and technical discussion about the Z3 roadster
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