1,797 votes out of over 2.3 million cast; that's was the margin of victory that former Assembly Speaker Thomas H. Kean of Livingston had over Representative James J. "Jim" Florio of Runnemede.
The Closest Gubernatorial Election in New Jersey History, both candidates were separated by eight tenths of a one percent thanks to a combination of Kean's strength in the then Ruby Red Republican Suburbs of Northern NJ, versus Florio's strength in South Jersey, Specifically Camden and Gloucester Counties - both of which he represented in the house.
The Campaign preceding this 50/50 race saw Florio focusing on his national record, and Kean focusing more on local issues; both attempting to position themselves as candidates of change, Florio as a change from Reagan and Kean as a change from incumbent Dem Gov Brendan Byrne
In Addition, due to the increasing unpopularity of Incumbent President Ronald Reagan, Kean sought to distance himself from him - with the former speaker, in an appearance with then Vice President George H.W. Bush, having H.W. try to disentangle the race from Reagan's disapproval. (Source)
In the end, After a close election night where Florio would look like he would win, and a costly, tense, monthlong recount where both candidates prepared to assume the governorship, Kean was declared the winner, with Florio conceding the race on November 30th.
Lastly, Kean won 21/40, LDs 12/21 Counties, and 9/15 Congressional districts to Florio's 19/40 LDs, 9/21 counties and 6/15 CDs