Unused wire from engine compartment needed

[Walt Fricke]

I'm adding a sensor to my (base car) 1977 Euro 2.7 (now an SC), and am looking for a wire no longer used to get the signal from the engine bay up to the dash area and into a data logger. The heater blower has been disconnected, and so has the rear windshield heater. I can get the 12V to power a 5V regulator to feed the sensor from the feed to the frequency valve test plug (because it now has an '82 SC motor with the FV wiring loom). Ground is easy. But I don't want to string another wire if I can avoid it.

The likely candidates seem to be involved with other functions sometimes. Any immediate thoughts? My head got a bit dizzy poring over the wiring diagram.

[rwest]

I think there might be a wire that feeds an optional rear fog light.

[Walt Fricke]

I hit on the wire which turns the rear window defogger on and off from a dash switch. It leads to a five pin round relay base. That relay has fused +12V and ground. I opened and gutted a relay so I could use it as a mount for a 5 volt voltage regulator (the sensor needs 5V), and just plug it into this socket. On my 1st rebuild of this car I was able to reconnect the rear window heater wires, but on my second rebuild I just couldn't do it so skipped that feature, so this was easier and better than trying to use the engine heater blower circuitry.

The in-car picture was to show the gauge and how I plumbed in the sender. I now have that assembly zip tied to the spark coil, and I may or may not make a better mount at some time.

The fuzzy pictures show reworking a relay, and the 60 plus feet of tiny wire which goes into a relay coil.

The graph was my quick and dirty, involving looking at the analog gauge, then moving to the driver's seat to read the voltmeter I had hooked up to the signal wire coming out of the dash where the defogger switch was. Looks pretty good, and linear. The top right dot is system pressure, after I turned the valve to read that.

Next I have to figure out how to program my fractious LM2 to display the voltage levels in Bar, and record them to see if they stay stable throughout track sessions.

[timmy2]

You could have used the solid green spare wire running from the bundle of wires at the back of the dash gauges to pin 2 of the 14 pin male connector at the rear panel.
(For future reference as you seem to have freed one up)

[Walt Fricke]

I see that on my schematic - also a brown/white wire from the chassis side of that 14 pin connector to "under the shift lever" or some such. Maybe that was for the Sporto? I must say that while I have had the shift tower off fairly often, I've never hunted around in the tunnel to see what unused wire connector ends might hide under there. That actually could be useful, as getting a wire from the back of the dash into the passenger compartment requires cleverness or drilling and grommeting a hole in the firewall.

For fluids there are bulkhead connectors, but I don't recall seeing the electrical connection equivalent, at least in one or two pin models other than standard audio or power plugs or for battery cable amperages - not fastons or ring connectors.

[timmy2]

The brown/white is normally taped to the through body harness under the shifter area for standard shift cars.
Should you ever go hunting for it.

[Walt Fricke]

Well, this project just got a bit trickier - the signal from the sensor, while it shows up nicely on a VOM, it looks like this on an oscilloscope:



And this signal confuses the LM-2, which must have a faster refresh rate or something than my VOM (which is digital), so is probably the reason the LM-2 display jumps around. On top of this, it seems that I can't program the auxiliary inputs - there are five, but one is dedicated to RPM. LM-2 has a way to program the two spare outputs, and to make choices if you hook up to the OBDII plug - should you have one. But not the spare inputs.

On it goes.