I had to replace the alternator on my 1998 Disco 1. I cheaped up and bought the aftermarket one. It did not have a spot on the 3rd 7v post for the RPM gauge to plug in, so I took the connector off the old alternator and put it on the new one, but it does not fit the same. The screw post has a built in nut that keeps the RPM gauge connector from sitting flush on the bottom, or from using the washers to connect it. After putting it on as best I could, the alternator is charging fine, but the RPM gauge is not working. I am sure it is because the connector from the old alternator doesn't really fit the duralast well.

Any advice? Anyone have a similar issue when installing an aftermarket alternator? I can drive around fine, but would prefer to have this gauge working as it can help diagnose other issues. Any help is much appreciated!

 

My '94 has the Duralast Gold and all the connectors are correct. Gold is new with lifetime guarantee, just got a free new one after 6 years of service. Turns out the '94 can start, but not run if the alternator breaks.

Pulley size is different between '94 and '96, so tachometers would read different if swapped between trucks.

The three wire connections at the alternator are B+ (brown) for the battery, D+ (brown/yellow) for the power to the regulator (through the indicator light on the dash), and W (white/grey) for the tachometer signal. The W signal is half wave rectified pulses through a 820 ohm resistor that could be inside the connector.