Your father is essentially correct. The First KKK, which was formed in the wake of the American Civil War and stamped out by the 1870s, did not include cross-burning as one of its rituals. This particular element was added in a work of fiction called The Clansman: A Historical Romance of the Ku Klux Klan, which was published by Thomas F. Dixon, Jr. in 1905, an unrepentant piece of apologia for racism, segregation, and most importantly the KKK, which was presented as a morally justifiable organization which was formed to protect white Southerners from the evils perpetrated by the freed former enslaved persons, who, in this disturbingly ahistorical vision, were able to satisfy their lusts for rape and murder upon their former oppressors kind-hearted, benevolent masters.

One element that Dixon incorporated into this clear work of fiction was the ritualistic burning of a cross, an element which he consciously adapted from what he understood to be an old Scottish ritual - "plac[ing] the order to a larger history of Anglo-Saxons" - and in the novel served a function similar to its historical roots, namely that of communication:

Issue your orders and despatch your courier tonight with the old Scottish rite of the Fiery Cross. It will send a thrill of inspiration to every clansman in the hills. [...]

Carry my summons to the Grand Titan of the adjoining province in North Carolina whom you will find at Hambright. Tell him the story of this crime and what you have seen and heard. Ask him to report to me here the second night from this, at eleven o'clock, with six Grand Giants from his adjoining counties, each accompanied by two hundred picked men. In olden times when the Chieftain of our people summoned the clan on an errand of life and death, the Fiery Cross, extinguished in sacrificial blood, was sent by swift courier from village to village. This call was never made in vain, nor will it be to-night in the new world. Here, on this spot made holy ground by the blood of those we hold dearer than life, I raise the ancient symbol of an unconquered race of men—

Dixon was hardly an historian though, and his use fit into the trend of Romantic fiction in the long 19th-century, or more specifically the tradition in the American South, where few authors could claim to have as much wide enjoyment and deep-seated cultural impact as Sir Walter Scott, whose historical romances enjoyed pride of place on the plantation-house bookshelves of the 'Old South'. Mark Twain famously wrote of him, with only some hyperbole perhaps:

Sir Walter had so large a hand in making Southern character, as it existed before the war, that he is in great measure responsible for the war. It seems a little harsh toward a dead man to say that we never should have had any war but for Sir Walter; and yet something of a plausible argument might, perhaps, be made in support of that wild proposition. The Southerner of the American Revolution owned slaves; so did the Southerner of the Civil War: but the former resembles the latter as an Englishman resembles a Frenchman. The change of character can be traced rather more easily to Sir Walter's influence than to that of any other thing or person

Not only in broader themes and style can Dixon's work be viewed, but specifics as well, as his exposure to this 'Highlands ritual' quite possibly came from Scott, such as this example in The Lady of the Lake: A Poem in Six Cantos which makes it rather easy to see why Dixon might choose to ape it for his own work:

When a chieftain designed to summon his clan, upon any sudden or important emergency, he slew a goat, and making a cross of any light wood, seared its extremities in the fire, and extinguished them in the blood of the animal. This was called the Fiery Cross, also Crean Tarigh, or the Cross of Shame, because disobedience to what the symbol implied, inferred infamy. It was delivered to a swift and trusty messenger, who ran full speed with it to the next hamlet, where he presented it to the principal person, with a single word, implying the place of rendezvous. He who received the symbol was bound to send it forward with equal dispatch to the next village ; and thus it passed with incredible celerity through all the district which owed allegiance to the chief, and also among his allies and neighbors, if the danger was common to them. At sight of the Fiery Cross, every man, from sixteen years old to sixty, capable of bearing arms, was obliged instantly to re- pair, in his best arms and accoutrements, to the place of rendezvous. He who failed to appear suffered the extremities of fire and sword, which were emblematically denounced to the disobedient by the bloody and burnt marks upon this warlike signal.

But it must be remembered that Scott was not an historian either, and if anything quite the opposite, the creator of national myths, his prose best understood in the context of the Highland revival going on in that time. The imagery of the cross he used several times, and the political underpinnings are probably best seen in the collection of pseudonymous letters to the Edinburgh Weekly Journal published as Letters of Malachi Malagrowther, where he resurrected the imagery in a conscious callback to 1745 - where "the Fiery Cross often made its circuit" - and a connection between Scots then and in 1826, when he was writing.

Dixon too, of course, was using the imagery in a similar fashion, connecting his characters to the Anglo-Saxon heritage that so many of Scott's heroes exemplified, and which many Southern elites had subsumed into their own identity (never mind that Highland heritage specifically would have been scant), and one that only became reinforced after the "War of Northern Aggression" as many Southerners came to identify even more with the Jacobite cause, or at least its romantic 19th century portrayal of "Highlanders [fighting] a rebellion to free Scotland against overwhelming numbers of Englishman [...] a lost cause to begin with".

But whatever both men's attempts to ground their heroes in the rituals of the centuries earlier, whether it was actually grounded in history is a whole 'nother matter, as Scott seems to have been drawing on questionable sources himself, at the least misrepresenting the usage of the symbol, and he "may well have invented the idea of the 'fiery cross'" at least so far as being an ancient ritual, as there seems not to be agreement that it was a ritual of the old Highland clans at all, possibly no older than the better demonstrated use by the Jacobites following the Bonnie Prince, but also an exploration which Allison frustratingly leaves at that.

Certainly historians of the period seemed to have a mix of perspectives, and at least somewhat similar to Scott's conception, so we perhaps can't place his on his shoulders alone. James Browne's A History of the Highlands and of the Highland Clans, written in 1834, included a similar ritual, although termed a "tarie" which he described thus:

Each clan had a stated place of rendezvous, where they met at the call of their chief. When an emergency arose for an immediate meeting from the incursions of a hostile clan, the cross or tarie, or fiery-cross, was immediately despatched through the territories of the clan. This signal consisted of two pieces of wood placed in the form of a cross. One of the ends of the horizontal piece was either burnt or burning, and a piece of linen or white cloth stained with blood was suspended from the other end. Two men, each with a cross in his hand, were despatched by the chief in different directions, who kept running with great speed, shouting the war cry of the tribe, and naming the place of rendezvous, if different from the usual place of meeting.

Another writer of the period, a Dr. John Smith who was a 19th century Gaelic scholar, similarly wrote of the "Cran-tara" being:

a signal of distress; that it was properly a piece of wood, half-burt and dipped in blood, which was conveyed with all possible expedition from one hamlet to another in cases of imminent danger.

In his 1825 etymological dictionary for Scots Gaelic, John Jamieson provides firmer, if vaguer, ground for the "Fyre Croce", with a record of royal use from the Registry of the Privy Seal dated Oct. 14, 1547, reading:

Ane lettre maid to Robert Weyr of the escheit of all gudis quhilkis partenit to Adame Bell (and others), and now partening to oure Soverane ladeis army and last field at Fawside besyde Musselbrugh, for resisting of oure auld innemies of England; incurrand therthrow the panis of tinsale of lyfe landis & gudis incontrare to our Soverane ladeis proclamatione maid therupone, the fire Croce being borne throw the hale Realme.

Although Scott himself wrote that he had been told of the ritual by those who had seen it first hand in the 1745 rebellion, these or similar, being the type of histories seen in the 19th century, quite possibly also helped to paint the image in his mind, and of course from there to Dixon. More recent discussion is scant, and what modern historians do make mention are much more muted in their descriptions, such as Michael Newton, who calls it the 'summoning stick'. Although he traces its use in raising an army as far back as Alexander I's reign in the 1200s, he also wryly notes that "fiery cross" is only an English affectation, subtly calling into question just whether fire was involved in the initial ritual at all.

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