Hi lads, I have a quick question for you, I have the T on my dash for the Tacho illuminated and the lorry won’t rev out. It also is leaving a black mark on the Tacho chart.
Is it a speed sensor on the box or the accelerator pedal? The wiring seems fine.
It’s an 2005 fm12
Cheers
John
Check the sender on the gearbox or it may be a wireing fault had the both on a 2004 reg FH12 it will have to be taken to a VOLVO garage to be put on the computer.VOLVO did have a batch of faulty tacho senders and the wireing is prone to failing and VOLVO have a replacment loom
Back to the dealers with that one buddy 
Had this as an intermittent fault on one of our 2005 FH XL’s. In the end it was traced to the tachograph loom multi-plug behind the dash. A couple of the connections were corroded. Worth having a look before heading down the dealers.
It is intermittent alright but is happening more often in the past few weeks! Can you tell me which plug it is? I checked the loom from the cab to the box and it was fine.There’s a speed sensor on the shelf in the shed I might just try it so. I was hoping it wasn’t the pedal as I think they are mad money. I had it go in a v1 fm but it had a flat spot rather than wouldn’t rev out.
Thanks for the replays lads
Regarding the plug ID if honest i can’t remember but i fairly sure it was positioned around the area where the steering column adjustment pedal is mounted. I had to pull the dash gauge panel, all the panels around the feet area and the pillar panel to trace the loom. I know it seem a weird place for a tacho multi plug but Volvo can place the tacho either in the dash by the radio or above your head, each position has a different loom which joins at the main multi plug. Hope this helps.
Thank you for your help, checked all of these, and cleaned all , fault disappeared!
Happy days
Cheers
John