Republicans will take care of some unfinished business Tuesday, deciding whether former Charleston County Councilman Curtis Bostic or former Gov. Mark Sanford will be their 1st Congressional District nominee.

The runoff election will conclude a packed and fast-paced GOP primary for the seat formerly held by Sen. Tim Scott, R-S.C.

Sanford and Bostic finished in the top two spots in the March 19 primary to qualify for the runoff. The winner will face Democrat Elizabeth Colbert Busch and Green Party candidate Eugene Platt on May 7.

Here is what voters need to know when the polls open for the runoff at 7 a.m. Tuesday:

Who can vote?

Not every registered voter in the 1st District can vote. Those who voted in the March 19 Democratic primary may not cross over and vote in Tuesday’s Republican runoff.

Also, only voters in the 1st District may vote.

The congressional district, redrawn last year, includes parts of Beaufort, Berkeley, Charleston, Colleton and Dorchester counties.

Other parts of those counties are in the 6th District. To find which district you are in, go to scvotes.org and check your registration under the “voters” tab.

Who are the candidates?

Bostic, a Charleston lawyer, served on Charleston County Council from 2001-09.

Sanford, a Charleston businessman, held the 1st District seat from 1995-2001 and served as governor from 2002-10.

To research The Post and Courier’s candidate profiles and other coverage of the race, go to postandcourier.com/first-district.

What to bring?

The runoff, like the March 19 primaries, will be one of South Carolina’s first elections under its new Voter ID law.

Voters are asked to bring one of five types of photo IDs to the polls: a state driver’s license, a DOT-issued photo ID, a new voter registration card with a photo, a U.S. passport or a federal military ID.

Those who have only an old voter registration card without a photo still can vote if they sign a paper saying why they do not have a photo ID.

The U.S. Justice Department sent monitors to the Lowcountry for the March 19 elections, but the department has made no public announcement of any problems at that time.

What to expect

Turnout is expected to be light, much like on March 19, when only 16 percent of registered voters showed up at the polls.

Those going to the polls are unlikely to wait long, if at all.

All the polling places will be the same as two weeks ago. In Charleston County, Mount Pleasant 10, 11 and 12 will vote at Sullivan’s Island Elementary (instead of Whitesides Elementary); while St. Andrews 20 will vote at West Ashley Middle School (instead of the Jewish Community Center). Those are new locations since the November 2012 election.

Tuesday’s forecast is similar to two weeks ago: clouds and a chance of rain.

What comes next?

Tuesday’s victor will face off against Democrat Elizabeth Colbert Busch and Green Party candidate Eugene Platt in a May 7 special election.

Reach Robert Behre at 937-5771.