Stree-jātaka-phalādhyāya of BPHS (Brihat Parashara Hora Shastra) defines Māngalika Dosha as follows :-
If Mars without any conjunction or aspect of auspicious planets is seated in 1, 4, 7, 8 or 12H ("H" represents house of Bhāva), then the husband dies.
If Moon is conjoined with Mars or Saturn in those houses, then the husband dies. If the groom's horoscope has this (Lunar) combination then the wife dies.
My Comments :-
This verse-49 is spurious, because normally Moon is a benefic planet, and Mars conjoined with a benefic cannot make Māngalika Dosha. Secondly, Mars without conjunction with Saturn makes Māngalika Dosha, hence it is senseless to say that Mars conjoined with Saturn makes Māngalika Dosha. During mediaeval era, some verses were damaged due to wear and tear of manuscripts and were reconstructed by pandits from memory which led to wrong verses sometimes. Traditional Jyotishis believe that this verse should have Chandra-Kundali, ie, Mars or Saturn with respect to Moon, instead of conjunction with Moon.
If widowhood yoga mentioned above is in male chart then the wife is destroyed ("vināsha"). But if such a yoga exists in both horoscopes, then it is auspicious.
This whole chapter should be studied carefully to get better sense. For instance, malefic placement of Mars in 8H leads to death, while malefic placement of Mars in Lagna leads to "sheela-guna-heenā" and "durbhagā" (foul character). Malefic placement of Mars in 7H causes Bāla-vidhavā-yoga, and if such a Mars is conjoined with Saturn then it leads to Garbha-srāva.
Therefore, Māngalika Dosha does not always lead to death and is modified by the house in which this dosha is present.
It is foolish to conclude that mere placement of Mars in these houses is Māngalika Dosha. Such a Mars must not be aspected or conjoined with any auspicious planet, and must have malefic aspect or conjunction or both by malefic planets to make Māngalika Dosha effective. Therefore, it is wrong to conclude that all occurrences of Mars in these houses will cause Māngalika Dosha. Effective Māngalika Dosha is present only in a small minority according to this definition of BPHS.
Moreover, no rule works in isolation (cf. http://vedicastrology.wikidot.com/#toc7). If there are benefic yogas, then malefic yogas get canceled or subdued. Lord Rama had Mars in 7H (Karka lagna meant Makara in 7H where exalted Mars was seated). But besides many other auspicious yogas, he had exalted Mars making one of Pancha-mahapurusha yogas, and he also had svagrihi Moon in Lagna with exalted Jupiter. Chandra yogas generally suppress other yogas. Had Māngalika Dosha been effective in his horoscope, it would have resulted in bāla-vidhavā yoga which means early death of Sita Ji just after marriage because this yoga was in Lord Rama's chart.