After the number of years that I've owned my 7 I have added various switches, lamps, etc. The problem is that it had all become a bit of a mess and I wanted to simplify the layout and un-clutter it all.
I did some research and from a value for money point of view Aim seemed to have the best range of all in one displays. I few years ago I saw a seven with a Motec dash and really liked a simplicity of having everything displayed in one place. Unfortunately I couldn't stretch to a Motec but Aim had a model which was very similar in the MXL. Some more research and there are three versions which mainly differ in the amount of onboard memory they have. I decided that I didn't want or need any datalogging so I was able to go for the base model which gave me all the channels that I would need: Revs, Road Speed, Oil Pressure, Water Temperature and Oil Temperature plus it had built in sequential shift lights, 6 programmable alarm lights. In addition to the normal items (above) to display I could wire in any 0-5v inputs I wanted and create custom sensors. This latter feature allowed me to input my wideband sensor and display the AFR in the 9-19 range. The software allows you to pick which input channels you want to display and a simple page system allows you to toggle through to the others.
The only snag was the fuel sender which is simply a variable resistor connected to a float. One problem is that the normal dial has built in damping, so it doesn't bounce around all the time. The other problem is that it isn't in the form of a voltage and so need converting. To fix the latter Andrew at Dataspares pointed me to info page on their website which detailed the use of a pull-up resistor to convert it to a 0-5v signal. To fix the latter was a bit harder and on the bench testing with a multimeter I could see that the signal was jumping all over the place. During a visit from my brother for my birthday I managed to raise the problem and he kindly sketched out a circuit that would electrically damp the signal over a period of time. I made up the circuit the following day and after adjusting a resistor value to increase the time lag I was happy with it. I tidied everything up and added it to the pile of sensors to fit to the car.
For the new dash and switches I contacted Richard from Carbon-Bits and got a list together for the switches I wanted (Fog, Hazard, Wiper, Washer, Cooling Fan, Wideband, Indicators, Flash, Main Beam and Lights). Everything arrived quickly, Richard delivering his well known high quality service.
The project took a bit of a bit of a lull while I finished off a living room wall building DIY project and then Christmas followed by a new year laziness got in the way. When I did finally get going things went pretty quickly. I ripped the old dash apart and removed the old dials and wiring in a day or so. I left all the old switches hanging in the loom so I could figure out the wiring for the new one easier.
The next task was to mark out and drill the new carbon dash. First of all I had to cut out the slot for the steering wheel bush so I could position the dash on the car and also give myself a reference point to measure from. I placed a lot of masking tape on the areas that I wanted to place my new switches and lamps. I then spent an evening in front of the TV with a square and marked out all the positions, allowing for the chassis tubes that would be behind the top and bottom edges. I got a tip from Mark to use a step drill and so I managed to borrow one and in one evening I made all the holes. I used a cutting disc in a dremel to make a slot for the dash connector to poke through. Job done - I had been very nervous of cracking the dash, but it was very easy as long as you take your time.
Once all the holes had been cut I was ready to stick it in place. I got some black silicone sealant for this job and put a very generous bead along the top edge and loads in the radius along the bottom. I then positioned it and wrapped masking tape all over it to keep it in place.
While this was setting I made a start of cutting out some of the unwanted wires. I found I could get rid of a lot of the red/white cables that feed the bulbs for all the gauges, plus the black grounds that go with them. Also for the chop were a lot of green power wires that feed all the gauges and some of the lamps. After a few hours the silicone had almost gone off (although I left the tape on for a another day to be sure) and I started to position the new switches and figure out the wiring. Most of the switches were straightforward but there were a couple of exceptions. The Hazard and Wiper were the two which weren't - the Hazard was simple to wire but because I was changing the lamp to an LED I had to add a couple a couple of diodes into the wiring for the indicator switch along with rerouting the one of the feeds from one of the relays. The Wiper was a bit more tricky and it required a call back to Richard to get the correct configuration as it is effectively 3 independent switches in one to ensure that power is maintained to allow the wipers to park.
Once all the switches were in place the next job was to fix the MXL in place and to figure out the wiring. I made up a spreadsheet for the connections that I thought I needed and sent this off to Andrew at Dataspares who kindly had a look and confirmed I had most of it right, but suggested using a 12v from the dash to feed the oil pressure and fuel sender. Making up the loom was simple enough although the pins are very tiny!
After a quick test to confirm all the switches worked I was able to refit wiper motor followed by the scuttle and then finally the screen. The next job was to configure the dash to suit all the sensors and this is done by assigning the channels and then deciding where you want them displayed and if you want any alarms to be assigned to a high or low value (such as oil pressure, AFR, etc).Setup Screen
The final job was to drain the fuel tank and calibrate it using the voltage reading on the dash - (some instructions). For this I simply unbolted the fuel line from the pressure regulator and directed it into a Jerry can placed on a box to get it at the right height. To get the fuel pump running I had to ground pin 20 of the ECU plug as the ECU had been sent away at this point (see K3 upgrade). I then created my custom sensor that would read 0 to 5000mV exactly as it received it from the sender unit circuit. When I was finally ready to start adding fuel to the tank I thought I had better just check that the readout was working correctly. So, I unbolted the sender from the tank and tried moving the float. Oh dear - I didn't get any change on the dash, that wasn't right, it remained hovering at 500mV. I did some poking about under the dash to check it was all plugged in OK and everything was as it should be. At this point my mood descended into my 'this isn't fair' depression and I resigned myself to having to pull most of the dash area again to find the problem. I removed the heater blanking plate to gain a little access to the back of the wiring and find my nicely protected circuit. I pulled this apart. I then started testing various voltages to make sure the Op-Amp was getting 12V and that the ground was OK. They were and it was. Next I tried removing the plug from the dash and seeing if maybe was getting a rouge signal. It stopped reading, which meant it was coming from somewhere. I then gave up putting off the inevitable and climbed upside down into the driver seat, knees over the rollbar and chin wedged under the steering wheel - oh joy. I stripped back the wired which I had neatly encased in some heat shrink and again checked for 12V. I also stripped back the signal wire and found a point that I could measure this from. At this point I measured ~1500mV. This was different to the reading on the dash so I really started to wonder what was going on. I got out of the car and moved the fuel sender and re-measured and sure enough it was changing (so the timer circuit was working as well). I reread my wiring diagram and it all made sense so I then looked at the user manual for the dash to check I was looking at the connections right. I spotted that the pin I was using related to channel 5 and something in my brain clicked. To make use of a 12v output from the dash I had swapped the oil pressure and fuel levels onto different channels from my original configuration. I hopped over to the laptop which was plugged into the dash and checked and sure enough, channel 4 was set for fuel while in reality I had wired it into channel 6 - so I was seeing the output from one of the other channels (AFR I think). It took all of 20 seconds to re-select the channels and put them on the right inputs and upload it to the dash. Hey presto, everything was now working perfectly. All I had to do now was tidy up the mess I had made of my nice neat loom during the last 3hrs. I left this for the next day. So, back to the calibration. This was easy enough, if a little boring and smelly with all the fumes. I could only get a 1/2lt jug to my filler so I ended up measuring after every top-up so I could plot a finer graph and select which points I wanted to use - at this point I didn't know what the graph would look like. So, 3 hours later and after two trips to the local BP station I had a brimmed fuel tank and a graph of voltage verses amount entered. I put in about 5lts before it registered anything and it stopped registering 2.5lts from the top of the tank, which I presume is the float hard up against the underside of the tank. I then went inside and played with the results to produce a new custom sensor which mapped the voltages against a percentage of a full tank. This will read 100% for the first couple of liters and when it shows 0 I will have about 5lts before the pump can't pull anymore out. I will add an alarm to the fuel channel for about 10% I think and see how it goes.
That was it - easy really, but quite good fun. I am very pleased with the result and intend to fit no more switches directly to the dash to keep it simple in design/layout. I have already added a new switch for the map switching on the K3 ECU, but I have done this out of sight using the old heater control cable position.

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