ok, i need to know where the two black vacuum lines coming out of the firewall hook up too. my engine is all aftermarket products. has carb. do they both hook up to vacuum port in the carb or what? any help would be appreciated.

 

What year/model car do you have?

I can only think of one, the heater control vacuum source, that actually comes through the firewall. It goes to the small nipple on the back of the carb in the stock set-up, but manifold vacuum is fine.

Unless you're thinking of the cruise control vacuum line. It doesn't go to the engine.

 

If these are both in the HVAC wiring harness, right below the heater hose nipples, then one is the vacuum source to the control head as described, and should go to the vacuum accumulator canister, which in turn should get its vacuum from a full-time source either at the carb base or the intake manifold. The other would go to the heater control valve.