Vehicle & Technical > Discovery

New battery, alt, belts, still no charge.HELP!

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jira:
We might have found the problem today.

There is a lead that comes from the back of the alternator and goes to earth as many of you know. The LR shop manual wiring diagram indicates there is an 820 ohm resistor inline with this lead. A phone call to a knowledgeable independent LR shop confirmed this, and were told to look for a bulge in the harness itself about 6 inches from the connector. We had tested the line for continuity previously, and it checked out fine. So today, thinking the resistor may have failed, we decided to check the amount of resistence in the line and recorded more than 4400 ohms. This was way out of spec and particularly odd since a failed resistor usually results in either an open or closed circuit. When we tried to follow the lead to find the resistor itself and check it directly, we didn't find it where we expected. Then we noticed an interesting jumper between two terminals on the back of the alternator. When we measured the resistance between these two terminals we recorded 840 ohms, clearly in the ballpark. So, that means the resistor is in fact built into the back of the alternator, not in the ground line itself as depicted in the wiring diagram. That also means there should not be any resistance in the earth line itself. So it appears we have a bad earth after all, but one that mimicked the resistor allowing enough current to show continuity, but providing too much resistance to allow the alternator to function correctly. I am willing to bet that this has been a progressive problem over the past 11 months, and that the resistance in this lead has increased over time. That is why the incidents have recurred in greater frequency here of late.

We test this hypothesis tomorrow by bypassing the old earth line with a new one. Wish us luck.

As a result of all this, our Discovery has a new name. Say hello to "Sparky".

John

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