99 yukon headlight fuse blows after engine has been started for about 60 seconds. have changed headlight switch and tail light assemblies on both sides. Does not blow when lights are just turned on and no engine starting

Headlamps and front parking lights/tail lights are usually fused separately on most modern vehicles.

The first position of the light switch would usually switch on the tail lights, number plate illumination, panel lights and front parking lights and the second position switches on the headlamps. From your description the fuse only blows when you select switch position 2 and the operation of switch position 1 is satisfactory.

If this is correct it would suggest a problem only with the headlamp circuits. This narrows the field somewhat which can be narrowed even further depending on whether the fuse blows only with the high beam or low beam. If it blows with both the fault must be common to both.
The use of a wiring diagram would be a tremendous help in tracing the fault but I suggest checking the bulbs first.

Yukon what ? XL , Denali , 2 or 4 wheel drive ?

My GM service info shows it as a 10amp not 2amp
TBC Fuse #60 10A is fuse #60 same yours ?

If front park lights are working highly unlikely headlight switch is the issue. Is the vehicle equipped with a trailer towing package and wiring to the rear? I would start there. This vehicle may also have a taillight module located under the vehicle on the passenger rear attached in the wheel well area that goes bad

If the fuse blows, you have a dead short to ground somewhere, likely around the tail lights or parking lights. Try this:

Get a box of the correct fuses.
Remove all tail and parking bulbs and put in a new fuse. If the fuse does not blow, try installing each bulb at a time to see which light assembly causes the fuse to blow.
Let's suppose its the RH tail light assembly. Pull it off the car and check for dirt and damaged wiring.

If this is an older vehicle, there may be wiring damage (due to rust) in the harness under the carpets.

Sure. It should also blow when the switch is on Park too.
The park circuit is hot in both park and headlight position.

First check the fuse, the clearance lights are not factory in most cases and the wiring gets shorted from poor wiring. Once you replace the fuse see if the lights come on, if the fuse blows right away find the wiring to the clearance lights and disconnect them, if the short goes away it is a I said the wiring is shorted. If you don't have the owner's manual you should be able to download it at the link provided. It should be fuse #10 a 20 AMP in the interior fuse box. http://www.fordservicecontent.com/Ford_Content/catalog/owner_guides/97ecoog1e.pdf

You can find wiring diagrams at http://www.bbbind.com/free_tsb.html free ! Enter your vehicle info. year , make , model an engine size . Under system click on lighting , subsystem click parking lights . Do the stop lamps work ? Turn signals etc.... Which fuse blows ? Also check fuse box diagram under power distribution ,fuse box .to see what all that fuse powers

MOST VEHICLES HAVE A CIRCUIT BREAKER BUILT IN THE HEADLIGHT SWITCH. OVER TIME THE CIRCUIT BREAKER WILL GET WEAK & IT WILL TURN THE HEADLIGHTS ON & OFF. YOU PROBABLY NEED A NEW SWITCH & THE FUSE BLOWING IN THE TAIL LIGHT CIRCUIT MAY BE A SEPARATE ISSUE.

does the fuse keep blowing ?? it is also on the same line as the cigarette lighter if the fuse is blowing check that there is nothing stuck in the lighter socket that is shorting it out. Could also be a bad ground wire not makeinig contact.

No interior dash lights and no tail lights on a GM usually means it's time for a new headlight switch. To check the fuse, it's in the middle of the fuse box marked instrument cluster. If the fuse is good, buy the switch. Lights blowing fuses means you either have a bare wire running down the driver's side of the truck or up into the tail light assemblies. There is also a plug in under the box on the driver's side near the bumper that may be getting wet. Hope this helps.