I’m trying to sus whether our 7.5t horse box is legal. It’s a “W” registration and is fitted with a Lucas Kienzel as the speedometer. I believe a privately owned horse box is exempt as long as the seals remain intact. I dont really know what a seal looks like although I can see an initial and the date 2002 written on the unit. Could this be one of the seals 
We use it for carrying our own horses to and from events. No hire or reward work.
some have red plastic seals.there is a wire seal on the gearbox which must also be intact.to get it sealed at a taco centre cost about 40 pound.hope this helps
when i had a horsebox a few years ago i just had to sign a form to say the vehicle was exempt from tacho graph rules and they didnt even check the seals and if i remember rightly i didnt have a seal on the gearbox as the cluch had been changed and never replaced it when box was refitted. best thing is to ring your local vosa test station and ask their advise, hope this helps
i seen this post last night and thought id ask the question for you whislt i was at test centre today with a trailer.
They WERE going to change the rules to do away with the tacho 'exemption ’ forms (like peteandbrenda says) but they have posponed this till next year. The only stipulations at present are -
the tacho head must be sealed and have the original calibration sticker in there (doesnt have to be in date). the calibration sticker (6yr) is the one what says the reg number I =, W = etc. The 2yr sticker is self explanitary!! 
By the way the dates on these stickers are the dates they were done, so they run for 6 and 2 yrs.
the only time the gear box has to be sealed is if its over 7.5t and in need of a speed limiter (yours doesnt need one because they didnt require them fitting till august 2001)
this came from the horses mouth 
so to speak!!
hope this helps