Thread: Help with Alternator problem

Is it charging (14.1v) ? Battery light off? Since a 120 amp alt is likely to be something other than a MM (the manufacturer of original Disco 1 alternators), the fact that the tacho isn't working properly doesn't necessarily mean the alternator is not working.

If the alternator is charging ok, identify it - maybe someone here has a workaround for the tacho output.

Originally Posted by River

Hello all,

A little help please, after a year and half absence of Land Rovers, I purchased a Discovery Series 1. Build 95 compliance plate 01/96 3.9V8 on LPG

Aware that it needed a new Alternator, I purchased one today and have fitted , as per the one removed, I stated it up expecting the tacho to start to work again and it hasn't although it now moves up to around the 300 RPM constant, disconnected the battery and the vehicle stops straight away.

Do i have the wrong Alternator? the one removed was 100AMP, the new is 120Amp

What have I missed? I checked the slow burn fuse and it looks intact?


Any advise is greatly appreciated!
Thanks Andrew

You may have swapped the 2 small wires on the back of the alternator. Brown/yellow? small wire goes via your dash charge indicator to the ignition switch. When connected to F(ield) it excites the alternator, light should be on key on, engine not running. Light goes out when running. The other little wire is your tacho feed, if connected to Field it won't read much. Can't help you with exact pic of terminals, if you can't get it going ask the other experts!

Back out in the rain again, it is a MM unit to suit 3.9lt and 4.6lt with air.

Re checked the connections and looks like the main brown wire wasn't seated properly, reseated and retightened, all appears well. 13.9 on the multi meter. can disconnect battery, and it still runs

Still no luck with the Tacho, When I remove the white wire from the alt it drops back to "0"

Could it be faulty Tacho?

Back out in the rain again, it is a MM unit to suit 3.9lt and 4.6lt with air.

Re checked the connections and looks like the main brown wire wasn't seated properly, reseated and retightened, all appears well. 13.9 on the multi meter. can disconnect battery, and it still runs

Still no luck with the Tacho, When I remove the white wire from the alt it drops back to "0"

Could it be faulty Tacho?