V40 TD Glow plug light not coming on
 

I've got a 1998 V40 TD and the glow plug light is not coming on and it has great difficulty starting when cold, running noisily when started. The tachometer has also stopped working at the same time. I've changed glow plugs apart from no. 1, but I think it's probably a relay or something but I've got no owners manual and the Haynes manual doesn't cover the diesel V40. Hope someone could point me in the right direction.

Thanks

hi a quick way to check rely is to remove connectors to glow plugs and check for live feed, ie put testlight between connector and earth,get someone to turn on the ignitionjust to lights (dont need to crank engine)if testlamp lights relay circuit ok. if not possible relay fault(may also be temp sensor fault)glow plugs dont need to work if ambiant temp/engine temp high.