My 1968 f100 brake lights and instrument lights alway stay on what could be the problem. I put a new brake light switch also but still stay on. Any suggestions please.

 

Brake lights and instrument lights are two, separate circuits that don't intersect with each other. If you said park lights and inst lights I'd say your headlight switch might be suspect, since you already changed the brake light switch. Assuming the brake light switch is adjusted correctly in that power disconnects through it when the pedal is fully upright, the next thing I'd look at is the fuse panel, and see if you have a short or cross connection there, where the wires or fuse clips may come in contact with each other. Beyond that, it's a matter of checking wires with a test light and pulling fuses until they go off.

 

They are in fact slightly related. But agree that one would not normally effect the other. So two separate issues.
But never, and I mean NEVER replace parts as a way to fix something. Not without testing first.
Any more, the parts that we can get over the counter are "presumed to be crap" and so should not be ignored as a potentially new gremlin.

So test your brake light switch with a volt-meter, or even a test light. See if power is coming on one wire (it should be) and going out on the other (it should not be) without the pedal being pushed.
This will tell you if it's the switch, or somewhere else.

The brake light power comes directly from the headlight switch, so that's the relationship I was talking about. But I've never seen one fail and be able to send power to the brake lights because the brake light switch should be blocking that. There is always power TO the brake switch, but should not pass through it until the switch is pushed.
I don't see anything internal to the headlight switch that could cause them to short circuit power to the lamps.

What year is your truck? Does it have hazard flashers?
Do the turn signals work as expected? The brake light circuit comes from the brake switch, up into the steering column and turn signal switch, before it goes out to the bulbs. This is so that the turn signals will still work when the brake lights are on.
The 4-ways however, will stop flashing when you press the brake pedal. This is one way to test the brake light switch without a volt-meter. Assuming that the 4-ways and turn signals work as expected as well.

Good luck.Lots more searching to be done...

paul