Basically hard question about '78 wiper wiring

['78Scottsdale]

Hello, ive got a '78 chevy blazer with intermittent wipers that constantly stay on. I figured it was the switch but when i bought a new one it didnt solve it. I noticed when i pulled the two plugs off the old switch and turned the accy. on, the wipers still ran. How does something still run when the switch is pulled? I noticed the two plugs from the wiper switch go directly into a small box. Im assuming this is some kind of relay? When i disconnect this from a one plug with six wires the wipers dont run when accy. is on. Is this the bug in the wiring or could it be before this box? I checked the plug that goes into the box with a test light. There are two hot wires one is light blue the other is black with a white strip.
I know this may be a long shot to find someone who knows the wiring of a specific problem of an older truck. Any help is appreciated.

 

[thorguy57]

sounds like the problem is in the black box. I don't have the schematics but it is probably a relay. On one side of the relay there is always power on the one side of it usually when the key is on. The switch will power the coil on the relay and pull the contacts in and send power to the wipers. If the contacts on the relay welded together the wipers will get power all the time when the key is on even if the switch is disconnected. Replace the relay and you should be in business.

 

[readymix]

That "box" is the delay module

 

[Kenny78]

What about a malfunctioning park switch?

 

['78Scottsdale]

Could the delay module then be doing this? I hope its not the park switch. How might i test if it is the park switch, besides buying new motor?

 

[readymix]

The park switch is part of the motor on my 87 but I could still remove it and clean the contacts pretty easily.

 

[Chevy305]

keep in mind the wiper circuit is a switched ground system. That means the positive goes right to the motor then the ground is what goes through the switches and delay module.

 

['78Scottsdale]

If the wiper circuit is switched ground system, then the wiper motor is always hot but needs ground to complete circuit. But how does the delay module or switch work with adjusting the high, low, and delay settings on the wiper without having a positive source to adjust?

 

[Chevy305]

If the wiper circuit is switched ground system, then the wiper motor is always hot but needs ground to complete circuit. But how does the delay module or switch work with adjusting the high, low, and delay settings on the wiper without having a positive source to adjust?

Not sure exactly how it works, but as I understand for High and Low settings it is just a resistor in series to lower the voltage to slow the motor down.