My wiper door is always up. It used to go up when I started the car and then go down but now it’s just up. The wiper control switch was trashed so I replaced it. I checked the activator with a mighty vac and can pull the door down when the pump is attached to the front port. It goes back up on the back port. With the engine running I can feel vacuum on the hose going into the back.

Is there anything else to check besides the relay.

Is there an easy way to get to the relay. Looks like the overflow tank for the radiator may need to be moved to access.

Thanks.

 

check your override switch under steering wheel could be in the down position

 

Another thing to check is the "Wiper Arm Valve". This sits on the passenger side and makes sure that the wipers are parked before the door can close. These valves are known to be failure prone. If you need a replacement, you want one with a black top. Ones with a White top are known to have issues. The vacuum system can be confusing. I am adding a diagram of the vacuum system.

 

@robertea My description wasn't 100% accurate. I replaced the Wiper Arm Valve (not switch) but the one I got from Corvette America had the white top. I think I saw a video somewhere on testing them. I'll dig that up and check it to rule that out. Do you know where to buy the ones with the black top? Thanks for the response.

 

there are two vacuum lines going to the vacuum relay, for it to shut there needs to be vacuum on both.
the hose on the top of the relay has vacuum to pull the internal sliding valve up which diverts the second vacuum source to the side of the actuator that closes the door.
when there is no vacuum on the top the switch is in the open position, which tells the valve on the back of the back of the tach to release the vacuum and the door opens. IF there is no vacuum there when it is supposed to be, check the safety plunger valve under the door, they leak, the wiper override and the tack valve.
if there is vacuum there then the relay itself is leaking past the plunger valve inside if the secondary source is there...very common tooo

if the vacuum on the side isnt there then thats the issue. It would be a vacuum leak at the reservoir tank, the one way valves, or the hoses.

If they are original hoses, cutting the last 3/4 inch of hose off all the connection points eliminates cracked ends or loose fittings


one thing I did to help find vacuum leaks is I bought a cheap ac vacuum pump from harbor freight and run a hose from the pump in another room and use a christmas tree remote to turn it on and off. You need a vacuum gauge teed in at the car so you can see when you get to 15 inches of vacuum so you dont damage any components. Keeping it in another room lets you hear the leaks...its stupid loud pump and it works a lot better than trying to use the hand squeeze variety

 

I don't know what the issue with the ones with the white top, but apparently, they are subject to failure. Corvette Central has both styles of the valve. The white top one is $37.10 and the black top one is $80.10. The price difference must mean something.
It looks like with the black one you would have to move the rubber boot from the old valve.