Call Crutchfield, see http://crutchfield.com.  Order a speaker ground
isolator, about $50.  Beats stringing wire, and is actually better to
boot. All your speaker grounds go to a common terminal on this unit and
the load is balanced across all of them with this.

It handles high power and has worked great for me!

--
Stuart MacMillan
Seattle

'84 Vanagon Westfalia w/2.1
'65 MGB (Daily driver since 1969)
'74 MGB GT (Restoring sloooowly)
'01 Toyota Tacoma (Something I don't have to fix!)

Personal mechanic for:
'70 MGB GT (Daughter's)

Assisting on Restoration (and spending OPM):
'72 MGB GT (Was daughter's, now son's)
'64 MGB (Son's)

Stripped and gone but their parts live on:
'68 MGB, '73 MGB, '67 MGB GT