How do i find a short?

lost the glove box users guide after 41 years? sure.
no problem told at all , some cars have fuses not in the box.
the left side drivers kick panel box>? that? or?
some are fuses, and others are CB , circuit breakers. some are fuseable links, one is below. or CB
eg:
Headlight and High Beam-one 22 amp circuit breaker incorporated in the lighting switch.
the drivers box is marked at each fuse. or seen just left of steering column under a cover.
fuse : dasy
#6 headlamps.
#3 turns and backup lamps
#5 hazards and stops
CB 20amp power seats and CB20 to door locks.
fuselink to IGNition switch
fuse link into and out of AMMETER GAUGE and to alternator
replacing alternator and not pulling battery cables first blows up the fuselink just above. (see schematics its all there)
fuse
#2 is AC controls
#8 AC clutch

why not get the service manual, and read it.
all fuse devices are there and full schematics
wiring.
https://eautorepair.net/Marketing/Default.asp


or

https://www.rockauto.com/en/catalog/ford,1979,thunderbird,5.8l+351cid+v8,1139981,literature,repair+manual,10335

The DLC has a separate fuse, F18 in the Smart Junction Box (SJB).

Maybe something wrong with cigar lighter socket? The top wire is voltage, bottom is ground for cigar lighter. If the voltage circuit was shorted to ground, it would blow the fuse w/o anything plugged in. If the component your plugging into the cigar lighter is drawing too much, it will blow the fuse.

How old is the battery?

The lighter has an element that get hot to light the cigarette. That element acts like a fuse as well. It will show an open to the coil if shorted out. Alsao the case this element sets into has a built in fuse. If that fails, the lighter will not work. Ohm meters are used to check these items out if all fuses in the fuse box are OK fine

I'll give you a list of possibilities:

Fuse (but why did it blow)
short in circuit
cigarette lighter recepter is worn , shorted or dirty.
open in the circuit.

Check them out with a voltmeter.

YOU HAVE A SHORT. OK THE LIGHTER ITSELF CAN BE BAD UNPLUG LIGHTER FROM THE BACK PUT NEW FUSE IN IF IT DOESNT BLOW CHANGE LIGHTER ASSM IF IT DOES TRACE WIRES FROM LIGHTER TO FUSE BOX YOU WILL AND CAN FIX THIS

I have seen car chargers that would blow the fuse. They were shorted out so look in the fuse box and replace the accessorie fuse and retest

Replace the lighter assembly, it is shorted, this is very common.