720 wiper system wiring - Common negative or positive

[matrophy]

I have an 86 720 2WD Z24 truck and I want to install an interval wiper module. I'm stuck at square one because the installation instructions are for either a common negative or common positive system. Are the wiper systems in my truck common positive or common negative? I believe that common positive/negative is different from positive/negative ground but haven't been able to find a strict definition of common positive/negative.

[datzenmike]

Power goes to the wiper motor (I say motor because they are, gas/fuel powered are engines) when the ignition is on. If the wiper switch is off but the blades not parked, they will now. If low speed is selected a ground through only some of the motor windings runs the motor at a reduced speed. If high speed is selected, additional windings are connected to ground and the motor runs at full speed. 

 

I don't know what your 'interval wiper' has for wires but probably needs a ground, a 12v and likely some way to turn the ground off and on to the slow speed windings. 

[matrophy]

How the module is connected is dependent on whether the system is 'Common Positive' or 'Common Negative' so connected to park circuit or low speed circuit respectively. So, solving that first puzzle is where I am stuck. I get the impression that Common Negative is not the same as Negative ground but I'm not sure of that. I believe it refers to the circuit and not necessarily to the whole vehicle. Here's the installation diagram. They are hard to read here but the connections on the module listed from top to bottom are: 12V+, ground, NO, COM, NC

 

[datzenmike]

Itr would be the top diagram. I assume that when the interval is turned OFF the wire directly above the word 'cut' is grounded.

[matrophy]

Thanks Mike, I figured it out. These modules are on eBay or from Qkits.com and is part number MXA041. The instructions that come with it suck big time.

 

As with a lot of this stuff, it's easy once you know how.

 

I added a diagram below showing what wire I ended up cutting. My truck is an 86 but the wiring diagram from an 84 matches the wire colors in my truck so I used that one. The diagram below is for an 84 without MIST or intermittent wiper. Presumably, the owner of a different year model can use this to figure out where to cut based on what each wire is doing. The wiring on the module from top to bottom is 12V+, 12V- to ground, NO to ground (I used a jumper for this), COM to switch side, NC to motor side. I did all my cutting at the motor connector since there was more wire to work with and the wires at the switch are generally different colors.