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