Hi Graham
I looked at this yesterday (on familysearch and on Ancestry, at lots of public member trees with conflicting opinions) and found that there didn’t appear to be any hard evidence (eg wills, family bible) to link up any particular John Taggart b circa 1803 to any particular set of parents. I’d be interested to know whether you do have any solid evidence that your John Taggart (bap as John Tygart in 1803) was the son of William Taggart and Isabel Christian.
Before delving into the likely parents of the William Taggart whose wife was Isabel Christian, it would be very useful to know all the hard facts you have on John Taggart:
At his marriage did he give his father’s name and occupation ?
What was the name of his wife and date of his marriage ?
Which of his children was your direct ancestor ?
Did he stay on the IOM --- if not, where did he go ?
Have you found him in all the relevant censuses ?
Do you have death and burial dates ?
Do you have family documents which give vital information ?
Have you been relying on research done by a family member from an earlier generation ?
Once we know more about your John Taggart, we can research with greater confidence.
Jean