Fitting a Tachograph


Unless you are only taking your bus with less than 8 passengers to historic vehicle rallies or for maintenance or repair you need a tachograph. This matter has been researched extensively by the owners of historic vehicles and there is a good summary of the legal position on the Routemaster Association’s website and a detailed account of the Drivers' Hours and Tachograph Rules in the UK and Europe.


This is how I fitted a tachograph to RM471 on 6th May 2005.


I had no working speedometer and there was a tachograph sender fitted where the speedometer generator should be situated. I decided not to repair or replace the speedometer generator and speedometer but fit a tachograph instead. Some owners have had a tachographs fitted in addition to the speedometer using pulses generated by the nearside gearbox sender necessary for fully automatic operation of the self changing gearbox but there are problems with this method. Anyway my bus does not have a nearside gearbox sender!


I fitted a new tachograph sender unit to a tachograph adapter on the offside of the gearbox where the speedometer sender is usually situated.



I routed the cable from the sender in the conduits (when I could) or cable clipped it to the conduits provided for the speedometer and gearbox cabling (when I couldn’t) all the way to the cab.


I bought a “scrap” tachograph head unit from a local commercial vehicle scrap yard and mounted this in the cab in the space previously occupied by the cab light.



The cable from the sender plugs into the back of the tachograph. Another plug supplies +24V, two –24V connections and a supply which is live when the ignition is on and another which is live when the side lights are on. It is easy to pick up these connections from the switch panel above and to the left of the driving position which includes the “coat-hanger” starter.


The new sender cost £67, the wiring cable assemblies with connecting pugs cost £80. I installed all the units and wiring myself. About two hours work.


Testing the tachograph head, calibrating it on a rolling road and sealing the sender and head cost £45. This needs to be done at a tachograph calibration centre.


The whole cost, including VAT (but excluding my labour) was just under £350. Tachograph discs cost about £4 for a hundred.


Wiring details


From sender unit to tachograph head


1-Black, 2-Brown, 3-Blue, 4-White


Power to tachograph head


1 +ve 24V permanent, 2 +ve 24V sidelights, 3 +ve ignition, 5 –ve, 6 –ve.


Part numbers


I needed a 4 pin “18” sender unit to match my tachograph head. The parts I needed to buy were as follows


MA204120-4 sender unit

ZT60755792 wiring loom

ZT 60795575 wiring loom




Being legal – Having an accurate speedometer – Having an accurate odometer (in kilometres) – having a clock in the cab




Isn’t an original feature – Need to change the disc every 24 hours and write in drivers name, start and finish location and odometer reading every day - keep the discs for inspection in the vehicle for one week and somewhere else for 3 months after that – the clock needs to be reset whenever the battery power is disconnected.


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