Alternator/Starter motor issues
 

A couple of months ago I replaced the alternator on my dads Range Rover. Since then there have been no problems with the battery or charging.

Today I had to replace the starter motor. As soon as we started up after putting the new motor on the dash computer flashed up alternator fault. The new motor fires the engine instantly.

A multimeter across the battery shows 12v when the car is turned off and 11.7v when the engine is on and the alternator is supposed to be topping the battery up.

Can an incorrectly wired starter motor A) start the car as normal and B) cause the alternator to break?

Or is it more likely to be a coincidence? It just seems strange that the alternator fault appeared the second we fired the car up with the new motor.

I assume you disconnected the battery before replacing the alternator? Double check your connectors, especially any earths that you may have disturbed. Check you are getting about 14 volts across the battery when the engine is running. Rangies can be a real pain for setting codes, especially if it's a P38 - quite often you have to reset all the electric windows and the sunroof after a battery disconnect. You will most likely need to clear teh fault code via a code reader.

It is a P38, when I did the alternator a few months back I disconnected the battery. After putting the alternator on the car ran fine until the starter motor gave up today. I haven't disturbed the alternator since then.

When I worked on the starter motor I also disconnected the battery. The only connections I undid were the cables that attach to the starter motor itself and the cable on the battery. All the connections were spotless when I put them back together and done up really tight. I'm certain I put the cables back on the starter motor in the correct places because the car starts perfectly.

A multimeter across the battery when the car is running on the new starter motor shows 11.7v

check you have continuity between the alternator main terminal and the battery, sometimes they go via the starter and this may have been missed breaking the circuit.

TT

I just got home from work and have done some continuity tests. There is a connection between the battery and the alternator but still no charge/not enough charge arriving.

I also did some continuity tests between the alternator and the connections on the starter motor. There was continuity on all four connections on the starter motor. Not sure if this is significant as they are both connected to the battery.

I did notice that one of the connection posts on the starter motoris sitting crooked and the plastic around it is cracked - if the post has moved inside and is causing a short, could this be causing the motor to have a constant draw on the battery which might cause the low voltage? Even though the motor disengages as it's supposed to.

I will be taking the starter motor back, it shouldn't have a wonky post and cracked housing. I didn't put excessive force into doing it up at all.

While replacing it I disconnected the positive terminal on the battery rather than the negative so that no power was going to the starter motor while I was working on it.

Is this likely to have caused any problems?

No short was created by the wonky post, all the plastic was doing was holding the end of the bolt in place. I am taking the motor back to be replaced as it shouldn't have snapped so easily.

Also, I have been told that I did my alternator/battery continuity test wrong. I did it using the postive connection on the alternator and the negative on the battery. Someone else has said I should have used the positive on both the alternator and the battery. When I did this I got no continuity.

Sounds like you have found your problem. There should be a thick lead comes off the alternator and goes to the positive of the battery. If there is no continuity between these two points that's where your problem is. If the starter turns the engine it's not faulty.
Enoch

All sorted now, took it back and got it swapped for another one. Works perfectly now with no alternator faults :D