Tamar Braxton and hubby Vincent Herbert had custom wiring installed at their home but went AWOL when the bill came ... at least according to a company that's now dragging the couple to small claims court to get their dough.

Crystal Clear Audio & Video says it spent multiple days working at Tamar and Vincent's Calabasas home back in December ... this according to legal docs obtained by TMZ.

The company is suing for the overdue balance, plus interest and collection fees -- $3,724 and counting. And now we're told the long overdue bill is affecting the small business as it struggles to meet payroll.

The case is set to go before a judge at the end of the month.