I have a 99 superduty diesel f250 the heater is stuck on defrost, no fuses are blown, i tried a new set of switches on the front still it doesnt help, i just need to no what to look at next,

There is one in the engine compartment and one under the dash on the driver's side.

Possibly some blockage? Foam where it shouldnt be?

check your vacum hoses u got a leak somewhere

I had a problem with vacuum in my F250 diesel. It had a new vacuum pump but would kick out of cruise control every time the vacuum pressure dropped. It turned out to be the vacuum reserve cannister had holes in it.

Seems you reach a tipping point and then all the vacuum systems mess up. You might want to check the reserve cannister and any vacuum servo your 4x4 might have. You can check most of the vacuum stuff with the engine OFF using a vacuum pump. You could have a leaking vacuum pot operating the ductwork. Check your diesel vacuum pump for output and loose belts.

Have you looked at your anti lock braking system. It will give a pulsation when it is in use. You may have a problem with it and it is coming on prematurely. Listen when your truck is doing this and you should hear the humming of the antilock system if it is on. Otherwise i would ckeck your ball joints and tie rod ends for wear as this can cause a vibration back thru your braking system as well

Sounds like a bad connection on the fuse links. You may be able to find a YouTube video on the subject.

diconnect the heater, if it doesnt blow fuses anymore, the heater may be shorted out.

change the fuel filter and if that doesnt help do a tune up

to what?

I have a ford f 250 4x4 2003 and my horn doesnt work and the overhead compass/information instrument will not turn on. the airbag light blinks a few times them stays on. whats the deal?
GETTIN SIK OF LIGHTS ON OFF