Eek.
There may be some standard wiring colors going on with it... but being so old, I'd hate to really even try.
Are there RCA connectors on the back of it? And a red wire, black wire, and yellow wire (in addition to two colored pairs.. one solid, one striped, of each color? Maybe white, grey, green, or purple?)
Seriously though - I'd skip the EQ.
The EQ is something that might be helpful down the road...when you've got a system that's fairly well ironed-out as is... good speakers, amplification, source unit...
Currently, you'll end up making very large adjustments that really don't seem to affect the sound much to the end of improving it... all you'll notice are tonal differences.
With a system that's ironed out, the EQ requires very small adjustments to make relatively significant differences in sound.
And even with an ironed out system - you'll end up swearing at your EQ. :P
I'd save yourself some headaches, and not bother.
It's like the bass and treble knobs, also... in the hands of those who aren't experts... you'll just find them simply cranked one way or the other... often "all the way up", by people that think they provide "boost".
Anyways, consider the questionable wiring a good excuse (just one of many - seriously!) to not include an equalizer in your system.
Whenever I can avoid it (quite seriously!) I don't include one in my cars.
Linear Mode
