Fuse for cruise control and back lights keeps burning out

how can I check for it to solve this problem - earlier it was suggested to look for loose wiring - but where? are special tools needed?

do i have to disassemble a lot? or better turn in to a garage?

could there be other reasons why the fuse blows out?

If you’re not up for finding the problem yourself, you should take it somewhere. Don’t keep replacing the fuse, You could start a fire. There was a big recall for previous year Sables because the power safety switch for the cruise control was catching fire or blowing the fuse.
Possible causes: Faulty component(s) or wire(s) rubbed bare somewhere and shorting out. With the factory wiring diagrams, you could check every wire and component fed by that fuse. This could involve much disassembly.

before I had the problem with the fuse, I was not able to shift gear from park to drive, I was parked on a hill, never had that problem before, I seemed to be stuck, I had to use force to shift, but since then no problem, could this be connected why the fuse is blowing, car is automatic-

I don’t think this latter condition has anything to do with the fuse that is blowing. You were parked on a hill and the parking pawl was doing its job in keeping the car from rolling away. When there is pressure on the parking pawl, it is hard to get the car out of park. When you are going to park on a hill, engage the parking brake before you shift into park.

As far as the fuse problem is concerned, start by having the module for the cruise control disconnected. If the back up lights function without blowing the fuse, you know the problem is in the cruise control. If the back lights blow the fuse, then the problem is in that branch of the circuit.

i replaced the fuse, i did not use the cruise control while i was driving, returning back home, i checked the fuse, it was burnt thru, so I guess there is problem with the back lights?

It could still be a short in the cruise control–perhaps something in the switches that activates the control. To isolate the problem have the cruise control disconnected and see what happens.

My son’s father-in-law had a Lincoln Towncar about the vintage of your Mercury. Everything was turned off in the car and the key was removed from the ignition. The car caught fire in the middle of the night and even though the car was parked outside the garage, the fire jumped into the eaves above the garage and considerable damage was done to the house. They were out of the house for the better part of a year. Just before the fire, the cruise control on the Lincoln had ceased to work The fire inspector thinks this cause the fire, although the Lincoln was burned so badly that it would have been difficult to pinpoint the exact cause. If I had your Mercury, I would have the cruise control disconnected immediately. If the fuse continues to blow, the problem is in the lighting circuit. If it doesn’t blow, then you either need to have the cruise control repaired or leave it disconnected. Just because the cruise control switch is off doesn’t mean that it isn’t receiving power.

what a scary story - I will bring the car to the garage tomorrow - if it is the cruise control and expensive to fix, I will have it disconnected if that can be done, with the back lights still working - since the car has not much resale value - I plan to drive it until it breaks down or unless it is unsafe to drive -
will see what the mechanic will tell me -
I will report back, what they find, cost…
any other advice how to approach the repair? the diagnosis will cost about $75 -

a bad MLP sensor was diagnosed, cost at dealtership: labor,tax, part, diagnosis: $272-
the a/c works again, the fuse holds, but the reverse lights still don’t work, because somehow the wire harness to reverse lights burnt or melted due to some shortage - which the garage only figured out when the new senor was in, the harness is not stocked anymore,the car is too old - a new harness once cost about $600 or so - way too expensive -

I would think that an electrical shop or a clever mechanic who understands electrical wiring could bypass the harness and make the reverse lights work. My Dad bought a 1954 Buick that didn’t have reverse lights and the dealer installed them at a reasonable price. I did the same thing with my 1965 Rambler–reverse lights were an option. I even put turning signals on my first car, a 1947 Pontiac, because turning signals were optional back then. When the horn switch quit functioning on my 1950 Chevrolet pick-up truck, I mounted a push button switch on the side of the steering column and connected it up so I again had a horn. This saved pulling the steering wheel.

At any rate, I’m certain that a good electrical mechanic could make the repair by bypassing the harness.

Has someone checked the brake on/off switch and the wires around it? It is right near the brake pedal.