peugoeot 406 will not start off the key

is the batt full? also is it the relay? bypass the relay by putting bit of wire from live side of batt to one of the glow plugs. only for a bout 10 secs.try that, if that dont work try the relay.

tried that first still wont start

are u getting diesel to the engine?but it still sounds like that the relay is not getting the power to it and passing it on to the glow plugs.so you have tryed a wire from live side of the batt to one of the glow plugs? chris addlestone

You could try the pre-glow plug method of starting but it does strain the battery if it is not up to scratch.

The method is:

Press throttle to the floor. Then turn the key to run the starter motor. After a little while the engine will keep trying to fire and then start to kick in. DO NOT let go yet, keep the starter running until the engine starts to rev.

If that works then your problem is almost certainly glow plug related. If it doesn't work, then you may have an air lock in your fuel line that needs bleeding. Again, the old fashioned way to do that was to slacken the pipe connection to the first injector and run the starter. As soon as fuel starts to escape from the joint, tighten it and repeat for all injectors. I believe there are more modern ways of doing it now but that method never used to fail.

That is the best method i have used many times.as it always work.it takes time.(well what dont now days)