Postby smj999smj » Wed Jan 13, 2016 1:03 pm
The tachometer issue is probably due to a faulty tachometer, which isn't uncommon in Nissans. They are usually expensive. The only way to be sure is to test the circuit. I highly recommend you get a factory service manual. You may be able to download one for free from Nico Forum's website.
For the temp gauge, you will have to do some testing. Find the coolant sender, unplug it and ground the circuit. The gauge should go to full hot if it's working correctly. If the gauge is working okay, then check the sending unit connector. If that's okay, replace the sender.