Measuring Coolant Temp

[Brianmoooore]

so I'll have to tap into the green one that feeds the cruise control... which has never worked. Hmmm.

You can use another pin. Most of the pins on the green socket are the same signal.

[Grrrmachine]

You can use another pin. Most of the pins on the green socket are the same signal.

What I mean by this:

...and I'm getting continuity between the OBC plug pin (yellow plug on the cluster) and the green plug that feeds the cruise control

is that if I put one electrode of my multimeter on the relevant wire on the OBC (brown/red), and the other on a pin on the green socket, then I get continuity. So it doesn't matter whether I use the green socket or the OBC wire, they should put out the same signal.

[Grrrmachine]

SOLVED! The problem appeared to by my Frequency-to-voltage design.

The F2V that came with my data-logger was based on a tiny LM2907N-8 chip - very minimalist design. That worked for the tacho, but not the speedo.

So I downloaded the datasheet for that chip and built another, using the same basic circuit board but with the bigger LM2917 chip. Again, worked on tacho, didn't for speedo.

Then I used found design, which is from a poster over on the e30tech webste:

http://foz11.tripod.com/DIY_MOD_s/Digit ... peedo.html

I assembled it with no modification, and the circuit accepted the 3.3V input (instead of the 8V recommended) with no problems. At 60kmh it pumped out 0.25V, rising steadily to about 0.375V at 80kmh. Since it uses the same LM2917 chip as before, the issue can only be with the capacitor/resistor layout.

Hopefully this will prove useful to others wanting to keep their existing gauges. Also, the link also explains how to convert your tacho pulse into an 8-bulb LED gauge... possible Service Indicator conversion?