TD5 Alternator tests?

[acgmarketing]

I have an issue in a 2000 auto TD5 disco. Had battery light on for a few months but voltage across battery terminals when on around high 13s spiking to 14s at times. Then 2 weeks ago car died on road for wife. Had nanocom in car and had wife give me voltage when ignition on (10.5v). Ran spare charged battery out and came home fine. Took out alternator and replaced regulator and brushes set - put back in with charged battery. Same result - high 12 when off and low 12 when running. Have been running around without accessories on for last few weeks scratching head and recharging battery each day. Today I put in a known working alternator today (ta Bundalene) and same outcome. Got new alternator on way from UK but starting to expect that will not change things.

I also have checked all fuses and bulbs (rear light suggestion) and all ok. Anyone got more ideas? What test can be done to the wires leading to the back of the alternator to check where fault may now be - I mean the little wires not the output charge lead. Oh and I have removed, cleaned and replaced all the earth connections I could find related to battery and alternator, the ones in the main fuse box area and one on driver's side lower front of engine....

[DeanoH]

Are you reading full battery voltage at the alternator output (big thick wire)with the engine stopped ?

I'd expect two thin wires on the back of the alternator as well, one for the alt. lamp and one for the tacho. Is the tacho operating correctly ?

Your original fault sounds like a crook diode to me, you get some output but not enough to run accessories, lights etc.

With the alternator spinning and full battery voltage on its output I'd expect full alternator voltage/current to be available. ie. at least 14.5 volts and rated output current.

Deano :)

[acgmarketing]

Hi Deano, thanks for the ideas. I figured something like a diode or otherwise within the regulator which is why I swapped out the regulator. When I did so I saw the brushes were fairly worn so replaced them also. But no go when put back into the car.

At all times we have had taco working fine and only battery voltage at the battery and at the cable from the alternator (measured at the top of the cable where it connects at the main fuse box which appears to be hard wired under the plastic to the positive connection from the battery as running or not there is only about 0.5mV across the batty positive connection at the fuse box and the alternator cable).

There is a set of three wires coming out or going into the alternator at the rear. I've just disconnected them with the alternator in place (mungrel of a job that one - move the coolant reservoir out of way and disconnect the cable from the alternator if you want to give it a go). Of the three inputs (or outputs), one has its own lead going back up the wiring loom. The middle one has its own lead also going back up the wiring loom but the other end one (plain brown colour) splices into the middle one maybe only 2cm up the wire from the connector. With ignition switched to "On" but engine not running I got battery voltage on the end of all three wires coming to the alternator. What I'm now not convinced about is whether the end brown wire is in fact making contact with its pin in the alternator as the connector for that wire seemed a bit lose and may not be contacting when the plug is pushed into the alternator. Haven't pulled it all back out again to check that one and NO way you could check with it in position!

Any other ideas people before I pull it again?

[DeanoH]

................................................. What I'm now not convinced about is whether the end brown wire is in fact making contact with its pin in the alternator as the connector for that wire seemed a bit lose and may not be contacting when the plug is pushed into the alternator. Haven't pulled it all back out again to check that one and NO way you could check with it in position!

Any other ideas people before I pull it again?

Brown is the colour LR use for direct battery power, the brown wire you're talking about, is it a thick one ?, if so it's the main power output from the alternator, it is also the main power input to the alternator from the battery. A poor connection here will give the exact symptoms you describe. It also explains why your new good alternator doesn't work. Might be a bugger of a job, but I reckon you've nailed it.

Deano :)

[acgmarketing]

Interesting re the brown wire and usual colour purpose. It is thicker than the other two wires in the connection block but whereas the other two might be 1 and a bit mm thick the brown one might be up to 2 mm thick. There is of course the one about as thick as a finger which carries the generated current up to the main fuse box area and to the battery.

The brown say 2mm thick one is only about 2cm long and splices into the middle wire so if it is supposed to carry battery voltage to the alternator it will only be doing so by coming along the centre slim one until the final 2cm where it splices out to the "thicker" brown wire and into the alternator. This is original wiring as far as I know. We are second owners and had it now for 7 years without anything in the logbooks about alternator or similar work before us and the prior owner was fastidious using LR workshops (unlike me!).

Anyone got the RAVE manual with wiring diagrams of the feeds into the alternator to see if this brown wire has been cut short at some stage in the past? I had RAVE on my old laptop but it died before I copied it off and now can't find the original CDs!!

[acgmarketing]

Well car is operational again now - imported alt arrived yesterday and 1 hour later I had the new one in and all charging again good. Still can't work out the wiring though. The wiring diagrams show only 2 wires feeding into the rear connection to the alternator. One from the dashboard for the battery warning light and one from fuse 24 (inside fuse box) - reference voltage? Mine has definateky got 3 wires going into the back but the third one is soldered/spliced into the one coming from fuse 24 only about 2 cm from the connector at the alternator. Anyone able to comment on if theirs has 2 or 3 wires at the connector? Yes I know it is damn near impossible to see the wires under the intake manifold but in case anyone knows .....