Re: Argo Tachograph Questions ...
I haven't seen you get responses from those who have been there, so I'll take some educated guesses. Maybe someone who's worked on them will chime in.
Disclaimer: I'm still a wannabe owner. I've worked on wiring in dozens of skoolies and a few transits in the past, but as a radioman I was just looking for power and ignition sense, removing trim to install antennas and cables, and trying not to screw the vehicle systems up.
The buses with tachographs I've worked on mostly used a different model. They looked more like a parking meter. I never touched them. I think they had the mechanical speedometer cables re-routed to the box. These buses usually had duct tape over the factory speedometer, so the drivers would reference the tachograph display. Yours doesn't, I presume both the speedometer and the tachograph work going down the road?
I tried googling for an installation manual, but no luck. I have to just guess.
In your Photobucket pictures, there are what appear to be at least three electrical contact fingers on the right side of the back housing up by the parking brake knob. I assume that there are also matching contacts (not shown) on the right side of the tip-down display. If you tip the display down, does the bus still start? If it does, you may be OK cutting wires, unless there's a lot of circuitry in the back housing.
I can't make out the protrusion in the center of the back of the display. Is it an electrical connector, or is it a coupling that takes mechanical rotation from a mating speedometer cable socket in the back housing? If it's mechanical, it's very unlikely the unit talks to the engine chip. The only electric part may be the clock. How many wires are there? If it's only three, they may be battery (clock power), ground, and an "ignition on" status indication for the graph.
Your bus may be new enough to use electronic speed sensing information instead. My guess is that if any signal link with the computer exists, it's just speed, or speed and status, etc. (But I've been surprised by unexpected new technology a couple of times in the past.)
If the tachograph wiring has any influence on the computer, I suspect it's likely just the "ignition" power might be looped through the tachograph to prevent driver tampering. My educated guess is that I don't think the device would be likely to affect the chip program parameters, especially since not all bus operators would think the benefits of the tachograph system would justify the cost, and they purchase and run buses without them.
What is your goal? Saving the battery only, or removing the device from the dash? The one photo showing the dial face is blurry, but it looks like there is a clock in the middle of the dial, which is not present on the Argo devices I can find on the internet. Do you care if the clock is wrong?
If it turns out the engine will not run without the tachograph, and you don't care about the clock, just the battery charge, you may be able to disconnect the battery hot wire and connect it to an ignition switched feed, so the tachograph clock only runs when the engine does.
Someone said "Making good decisions comes from experience, experience comes from bad decisions." I say there are three kinds of people: those who learn from their mistakes, those who learn from the mistakes of others, and those who never learn.