A few months back I put in a 78 wiper motor and wiring so I could have the intermittent function. In that process I had a problem with the wipers wiping for no apparent reason. Here is where I investigate and show you how to do the same and do it right the first time.
I started this conversion off the 73-87 chev message board. Others have done this as well, but this is the post and pic of 67-76 wiper wiring I used to get going.
After a little more reading I got to this 78 version.
Eventually, with some help from the chev forum I noted above, I found this helpful pic. I don’t seem to have the post anymore or the guys name that posted it but it was a great starting point.
Why so many pics of wiring diagrams you ask? This conversion is all about the wiring in my opinion. I have one more for you- the final one used in my 76 with a wiper motor and wires/ connectors from a 78 gmc.
If you compare the above two photos, you’ll see that wire number 91,94,93,92 & 93 can be different colors. I traced my out and buzzed them with a volt meter to make sure the color I had at the switch and cab side of the firewall was indeed what I had in the engine bay beyond the firewall.
You’ll also notice that the #97 wire needs to be added as pre-78 trucks did not have it as a seperate wire in the harness for the park operation.
Here is a pic of what I had at my harness. If you look above the red crimped butt connectors, you’ll see my colors that correspond with the final wiring photo.
From here I bought the switch from Napa and delay unit with pigtail from a wrecker (wrong). You can read about that install here. Mounting the 78 motor wasn’t difficult. Take pictures when you pull it apart so you can remember how it goes back together. Here’s some of mine in progress;
The problem I mentioned above about the odd and varied intermittent wipe is now called the “phantom wipe”. Found here at the fountain of all things square body. Great bunch of guys there with experience in all kinds of issues. I digress. The problem is the “pulse wiper controller” or delay module. It has died somehow. I’m not sure how to test for it, but I ordered one from Rock Auto for $86 CDN to fix my problem. It’s the last item on the bottom of the page. Many thanks to 406 Q-ship in the forum for the heads up.
Thirsty Wrencher 