Here's a good link for troubleshooting headlight problems http://www.corvette-101.com/vacuum.htm the text is good and here's the corrected diagram, PG.

 

My driver side light was slow coming up and sometimes would just come up half way. With the head light problem, look at the actuators and see if the rubber boot is torn. Look at the shaft that the rubber boot is on and see if it corroded. I had pull my actuators, clean the shafts and replace the rubber boots.

 

thanks, I just looked at them and the boot is bad. is it hard to take those off? also I was wondering, there is a round thing that sits right under the washer fluid holder that has two lines running from it one goes the a hard line that runs down the frame headed to the back, and the other rubber line runs up about to the brake master cylinder, where its been cut. I know when I bought the car that the motor had been replaced with a crate motor, whoever put it in didn't seem to care to much about putting it in right or hooking everything back right! So did a 74 have a shut off valve when it was new, or is that something that the motor installers did not put back in.

 

Actuators: In the Book they say to remove the grill to remove the actuators, I had a helper raise and lower the hood and took them out from the top.
The round thing might be the Vapor Canistor, one line goes to the tank and the other "T"'s with the PCV valve and then connects to full manifold vacuum at the carb.
My car came stock with A/C and the hot water shut off. Here's the one I took out. PG

 

PG: Did you ever check the heater return line w/ the A/C on and the engine hot? I put a manual valve in my supply line and the heater core still would get hot after awhile from the return line so put a valve there also.

Since I put my own A/C in, wasn't aware of a valve in '73. Thought they started in '75 but since yours has one, then maybe mine should to. Will have to look for a vacuum port on the control head. If it does, might put a vacuum controlled valve in each heater line.

 

Hi 73shark, yes, after a long ride the other hose gets pretty warm. A second ball valve or a second correct vacuum shut off might let the A/C work a little better. PG.

 

That's kind of what I thought. If I can find a controlled vacuum port, I'll put in two valves. Otherwise will just stick w/ the two manual ones.

 

Hi, I'm resuming this post because I'm the new owner of the car and would like to fix the heating. Car has on AC, so is it supposed to have the cutoff valve? I dont find anything about inside the AIM...

 

Welcome to the forum.

I believe the heater control valve was only on A/C cars but couldn't hurt to put one on as these non-A/C cars on a 90*+ rainy day are a sauna. Main reason I put A/C on mine.