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87-93 D21 Intermittent wiper upgrade

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I will preface this guide by saying I'm bad at taking pics of my work while I'm doing it cos I'm always in a hurry, so this guide may be a bit light on my personal photos. However, this is still a much simpler upgrade than I anticipated having mostly worked on nonsense GM wiring before I got this truck.



Wire tools (cutter, crimper, stripper, etc)

About 10-12 feet of 2 different color wires

4" zipties 

Normal size zipties

A good quality electrical tape

Intermittent wiper stalk (cut the harness-side pigtail connectors for the switch & volume control off  if possible!)

Wiper amplifier (cut the pigtail off this too! You can't connect the amp at all without this pigtail or another FEMALE 8-pin connector from elsewhere on a donor!)


Step 1 - Remove the 5 screws on the lower face of the column. 


Step 2 - Remove the 2 screws holding the stalk to the column


Step 3 - If you weren't able to get the volume control pigtail, cut the wires 1.5 - 2 inches away from the 2-pin volume control connector on the new stalk. Set this plug end aside for later. See steps 7, 8, & 9.

I haven't tested this, but I believe the later style 'round' stalk is wired identically with the exception of the volume wires being moved to the 2 vacant pins on the 8-pin stalk connector. 



Step 4 - Remove the glovebox & the steel cover plate behind it. There are 2 plastic pivots at the bottom of the glovebox, these have tabs on their ends. Pull these pivots out by the tabs & open the latch to remove the glovebox. The steel cover has 6 screws & is pretty self-explanatory.


Step 5 - On the firewall at the upper left of the passenger foot well there is a grommet. You may have to peel back the top of the carpet & the firewall jute to find it from the inside. Pop this out & cut a slit into it with your cutters or a utility knife. Note: I don't know if this hole is in use on trucks with stick shift / 4WD / AC, as my truck has none of these options.


Step 6 - Run your 2 colored wires thru this grommet across to the column. You can use the bendy wire holder tabs on the heater box to help route these alongside the OE harness. Leave about 3-4 feet of wire outside the grommet.


You can ignore steps 7, 8, & 9 if you have the harness-side pigtails / connectors for the stalk & volume control switch.


Step 7 - Remember the volume control connector we cut off earlier? If you weren't able to get the pigtail off a donor truck, carefully cut open the plastic plug holding these pins. Remove one of the pins & splice the wire end onto one of the 2 wires you ran thru the firewall. Connect the remaining new wire to either wire from the volume control. Note: The polarity of the 2 wires from the volume control DOES NOT MATTER.


Step 8 - Carefully remove the keeper cap from the back of the stalk connector. There are 2 tabs on the short sides of the connector that need to be pried outward for it to release.


Step 9 - Push the new pin into slot 15 on the wiper stalk connector. This will be the only unoccupied corner pin on the original connector to make it easier to remember. Make sure the pin is oriented correctly when inserting, otherwise the catch tab won't hold it in place. Push the keeper cap back onto the stalk connector after checking continuity from the pin to the end of the new wire.


Step 10 - Now, we enter the main wiring portion. I did make a diagram, but I honestly ended up consulting my written notes more than the image while doing this. I strongly suggest all splices use the 'poke and wrap' method rather than butt connectors, this is what the small 4" zipties are for. Those orange picks from HFT or a voltmeter probe work well for spreading the strands apart.



GREEN pins are wires that keep their existing connections.

GREEN splices (circles) are pre-existing.

WHITE pins are ones that need changing or are added.

BLACK pins need no connection. 

BLACK splices are new splices that need to be made.

BLACK bars indicate a new connection from the original harness to the amplifier harness.

The PURPLE & YELLOW wires represent the two new wires you ran thru the firewall.

If you cut off the amplifier pigtail, PURPLE will be connected to the wire from the extra pin you inserted into the stalk connector from step 7, and YELLOW will be connected to whichever of the two wires from the volume control isn't spliced into ground.


Note: The polarity of the 2 wires from the volume control DOES NOT MATTER.



These are the written notes I mentioned earlier. 


New connections
NEW WIRE from PIN 15 from switch connects to WHITE/BLUE on amp
BLUE from motor is moved to BLUE from amp
PIN 13 BLUE from switch connects to BLACK/BLUE from amp
NEW WIRE from volume control connects to RED/BLUE from amp


New splices from motor
PIN 18 BLUE/BLACK splice with BLUE/BLACK from amp
BLUE/YELLOW splice with BLUE/YELLOW from amp
BLACK splice with BLACK from amp


New splices inside

EITHER from volume control splice with BLACK from stalk connector 



Step 11 - Test the wipers. Even on the fastest setting the delay is fairly long compared to a modern car, so don't be fooled! 


Step 12 - Secure the amplifier box. If you didn't get the firewall mount bracket, you can ziptie it to the cylindrical portion of the wiper motor using a long ziptie like I did. Try and make sure the connector faces at least a bit downward to discourage water from running in there. If you have any more wires you wanted to run into the cab (audio equipment, fog lights, winch) now would be a good time.


Step 13 - Secure the wires running thru the cabin & the engine bay. As seen in step 5 the brake lines are a perfect place to ziptie to.


Step 14 - Reassemble the interior (duh)


And that's all there is to it! I hope y'all find this guide to be of some help.








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