charging and tach issue.

[simpson110]

to start i replaced the alternator because i would lose voltage when the headlights were on and now that problem is fixed. but now in order for my rover to charge properly and the tach to work i have to rev it to about 3k rpm then the tach works fine and the voltage is also fine. now my question is what the hell could be causing this? any ideas would be great, and a wiring diagram for an '89 rrc with a 3.9l would be helpful. i just replaced everything as it was but i think someone had fiddled around with it before i got it, so that could be part of the problem as well.

[Jerry 92RR]

Sounds like you have a bad connection somewhere in the wiring. You've checked the battery with a multi tester; now check the voltage at the alt and see if they are the same. You may lose .05 volts from the alt to the battery through the cable but that should be the most. Check all (battery/charging) connections, clean with a wire brush and check those GROUNDS!

My money is a bad/corroded connection under the hood. Possibly a bad alt was installed, too. It happens, I have gone through a bunch of alt's until I bit the bullet and bought a 140am through Roverconnection.