Glow plugs.

[duckhunter27]

I have a CT 335 my glow plug light started not coming on when I turn the key on if it's warm out it seems to come on and work fine but if it's cold it will not come on. Any ideas what could be going on I was wondering if it might be a relay. Thanks

 

[winston1]

Do you know the glow plugs are not working when light isn't coming on? Not likely, but maybe just a loose bulb? My CT235 light does not come on in hot summertime or after running a while and then recranking. I suppose there is some sort of heat sensing that controls the light. However, your situation seems to be just opposite.

 

[duckhunter27]

They are not working tractor won't start when light doesn't come on in winter.

 

[winston1]

I believe your preheat relay is on the firewall (3rd one in on right hand side). Many of those relays are identical. Might try swapping and see if it makes any difference.