Like others have said right above the emergency brake. But since you didn't go to much into specifics on your wiper issues I'm going to point out the wiper motor ground a well.
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See that copper thing that runs from one mount leg to the other. This is the most overlooked wiper problem, and all sorts of interesting things will occur if it's not good enough.
This is something I wrote in another post, but it gives a good explanation of the ground tab, and shows a picture of a ground that likely to be problematic even though the owner thought it was ok.
About the ground, each mount has a rubber isolator that the bolt goes though. Only one acts as a ground, Two of the mounts in (in the below picture) are in view, the upper one is NOT a ground the lower one IS the ground, that metal tab which is riveted to the body of the motor on one end and sandwitched below the metal mount is the only ground it has and by the way it looks terrible. Wire wheeling the surface you can see will help the bolt to mount contact, but does nothing for the tab part. If that metal mount is as rusty on the underside as it is on the front. Plus that bolt makes the contact and that surface area is rusty, heck even the threads in the bulkhead are rusty. There is no way that ground is working properly. If this is a restoration project, or you care about it looking correct, the rubber mount will pop out you'll need to get to get all metal parts in relationship to the ground nice and clean with all rust removed and then coat all surfaces in dielectric grease. An easy way would be to cut a 6 inch length of wire, put two eyelets on each side, drill the rivet out of the current ground, clean the metal up there, and secure one end of the wire to that spot with either a screw or small nut and bolt. Then the other end of the eyelet can go around one of the mount bolts after the bolt is cleaned up, and do the best you can to clean up the threads on that bolt hole, if you have a tap that would work or just do the best you can running the bolt in and out a few times and spraying a bunch of penetrating oil in there to help with the clean up. Coat all connections in dielectric grease. Not only will that help the contact now, but it'll help prevent issues down the road.
Below: I circle the entire ground unit on the motor in yellow. The rivet in red and the mount in blue, note that the tab goes under the mount so cleaning the top of the mount won't help the tab connection. Let me know if this all makes sense or not.
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