My car has a braided ground wire for the lighter. It connects to a small tab under the dash, centered behind radio console.
EDIT:
The book says Metric 1 = 16 AWG is the size of the cigar lighter wire. Here is a pic of that braided ground wire. The manual says the lighter ground runs thru the C36 connector and is M2.6 = 12 AWG. The ground shown is direct. My spider came with a Coupe's radio console...maybe this was swapped as well. This ground does not look home grown.
