Hi,
I really hope someone can help with this as I am tearing my hair out
trying to find someone to ask!
I have a 1999 Isuzu NQR 7.5 ton lorry fitted with a horsebox body,
used for private transport of our horses and taxed as private HGV.
To prevent the batteries going flat when not in use we have an
isolator fitted. When the isolator is screwed in (to make the
connection) the speedo needle on the tachograph slowly goes from 0
round to maximum and stays there. If the front of the tacho is
opened the needle drops back to zero but will then not read
anything. It is as if the drive head stays at maximum even though the needle springs back to zero when the front is opened. The odometer part of the tacho works fine. I presume this is some kind of start up sequence but don't know how to reset
it so that it works. The tachograph worked perfectly until the battery was disconnected to fit the isolator. Although we don't need to use the tacho as it
is a private lorry this is our only speedometer.
The tacho is an analogue Veeder Root model (I think model number e10) with switches for 2 drivers but I can't find anyone who knows about them.
If there are any lorry drivers out there who remember the "old-style" tachos and know what the answer is then please let me know!
Many thanks and here's hoping...
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Hmm; a lot of odd things there. I did once see a VDO do this on a Merc horsebox after repairing some circuit damage, but I never did find out what the eventual fix was.
Why do you need an isolator? Unless there was something draining, then it won't stop the batteries going flat. Acid dust on the batteries is the main problem on horseboxes. Clean the battery tops spotless.
The memory/clock feed to the tacho should have been connected to the live side of the isolator anyway. Try re-connecting it, either with the front open or the speed-sensor plug out; it should go to full scale and then return to zero. Check also that there is still an ignition feed - blown fuse etc?
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We had a problem with the batteries going flat (the lorry doesn't get used that much) and the perceived wisdom at the yard was that it was the tacho that was draining the batteries. With the ignition off it still whirrs away turning the disc round and if left for two or three weeks seemed to be enough to drain the batteries enough that it wouldn't start. The isolator is a "discarnect" connected between the neg terminal and the earth strap to the body and has certainly stopped the batteries draining, albeit with the side effect I described.
The clock on the tacho goes round when the isolator is connected but obviously stops when the isolator is unscrewed.
There is a small push button on the front of the unit between the 2 drivers switches but have tried pushing this in case it was a reset button but no joy.
If you connect the isolator when the front of the tacho is open the needle obviously doesn't move but the needle drive inside the tacho still goes from zero to max and stays there.
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