1998 Land Rover Discovery
Well my tachometer was going crazy. Sometimes it would work and sometimes it would not. I removed my belt and spun the alternator and it sounded like the bearings are dry. I looked around online and most people solved this problem with a new alternator so I went and bought a new one. $400 and I still do not have a tach that works all the time. I have replaced my alternator, belt, and tensioner. All wires are tight. It drives me crazy. Sometimes it works great and other times it doesn't work at all!!! If I had a wiring diagram I would check that out but I do not. HELP!!!

 

Man this is a tough one.
99.9% of the time the tach fails it is because of the alternator going south.
All I can suggest now is to look for bad grounds.
www.atlanticbritish.com, tech tips, Discovery...there is one for looking for bad grounds.
Just thought of this, is yoru belt routed correctly?
AB has a diagram for that too.

 

Check the wire leads that connect to the alternator. Make sure there is no (green) corrosion on the terminals.

 

Sounds like a similar problem I had a few years ago. I have a 95 Disco series I, and as I was driving down the freeway, the entire car shut off and would not start to save my life. I had to have it trailered back to my house. It never happened again on the freeway, but it happened in town where the car would die, then I let it cool down for a while, and could get it started just enough to get off the main road. Just setting up the trouble for the easy fix it ended up being. My dad, rover guy extraordinaire, cleaned off the grounding wires, and I haven't had a problem since. If you need help finding the grounding wires, let me know and I'll get back to you. Hope this helps

 

check the small wire on the back of the alt, make sure its not chaffed and touching ground anywhere. was there any upper engine work done shortly before this started happening?

 

Truck has been like this since I bought it a few years back. Where are the ground wires? This may help. I do know there is one on the starter mount bolt. I have checked the little wire going to the alternator and there is no corrosion and the spade fits very tight. Other than that this thing runs great it just drives me crazy never knowing if the tach is going to work or not or if there is something else wrong making this thing not work. Help me please!

 

Download a RAVE manual off the internet and you'll have all the wiring diagrams you need.

 

Searched my harness and found the wire had gotten a hole rubbed in it and was shorting. Fixed wire and tach works great! Thanks everybody!!!

 

good to hear its fixed, too bad it was after the new alt.

 

Well, at least I have one less thing to worry about.