Originally Posted by bmwconnect
Fairly straight forward install....
Most important is a nice ground point to reduce noise or interference
And make sure to use the SAME ground point as the ECU. Otherwise you will see an offset in the ground voltage based on load and overage voltage. Many people simple ground the LC-1 directly to pin 10 on the ECU in the E30. (The ECU chassis is fine.)
If the heater has its own ground, it can be grounded to something more substantive but there is really no need, it can all be grounded to the ECU.
My ECU is grounded at the shock tower with a factory wire running 22" directly to the ECU. I ground the LC-1 there and tested the ground offset.. it was 0.02V which is still enough to cause a slight mis-reading, but good enough for me. You cannot compensate for offset via calibration because the degree to which it's offset varies with overage voltage and more importantly as the load through the ground circuit changes. Literally turning on the headlights could change the reading.