daddydonuts Posted August 24, 2012 Author Share Posted August 24, 2012 Reading your post reminds me that I think the polarity of the two posts are reversed for the 3 wire vs. the 4 wire? Take a closer look to see if that's the issue. Those are hooked up correctly, this vid was a 3 wire 280z tach, same as my stock 73 240Z except light bulbs were on the 280 harness Quote Link to comment Share on other sites More sharing options...
Zmanco Posted August 24, 2012 Share Posted August 24, 2012 Just took a quick look at one of the dead tachs in my bone pile and there's a metal strap that wraps under the plastic guide around the studs on the back of the tach. Because the polarity is opposite for the 3 wire (vs. the 4 wire), you have to move that strap to the other stud. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted August 24, 2012 Author Share Posted August 24, 2012 Just took a quick look at one of the dead tachs in my bone pile and there's a metal strap that wraps under the plastic guide around the studs on the back of the tach. Because the polarity is opposite for the 3 wire (vs. the 4 wire), you have to move that strap to the other stud. It is on the correct stud. I changed it when I tried the 4-wire tach I bought and had no luck either. The original stock tach in my car is a 3 wire, the 280 is also a 3 wire tach and that one is currently working outside of the tach housing that is in the video. I think the metal tach housing has to be grounded also. Thanks for helping Quote Link to comment Share on other sites More sharing options...
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