Fan not working. 98 w900

Also, you say it wont come on automatically, but does it do so manually (switch) (nm you answered that)
Also does it cycle with the ac?

At what temp is it not coming on that you think it ought to?

Look in tstat housing (on a cat), ground the wire that slips over the sensor post, if it still doesnt work, try tracing your wire first

Edit
Check your fan switch wires, at the switch, should have 4 wires connected to the switch posts

 

Run defrost or ac setting, blower motor issues be ######, if ac system is good, it should kick fan on in 2 minutes or less, that circuit is not on the ecm in a w9.

That said, check your fuse box... i think we all assumed you did that, but try tgat first/again

 

Have you checked the fuse? Last six of VIN and I will get diagram.

 

VIN is for 98 T600 with a Cat. Cat controls relay pin 86 to operate solenoid valve. Usually override switch gets power from 15 amp engine fan fuse and bypasses relay. Re post your last six.

 

Here is the diagram. About same as Cat, ECM controls 12V side of coil on fan relay. Unlike Cat, the fan overide switch also is input to ECM.