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Discussion Starter #1
Firstly, sticky has been (mostly) done and results are below. My questions are twofold:
(i) will a brand new battery and a non-functioning alternator be likely to get me home (about an hour’s drive, a bit over that in traffic, lights won’t be in use) or will trying this be likely to drain the new battery?
(ii) Given the excitation voltage I’m seeing on the alternator (6.23V on yellow/brown wire) is the alternator working (i.e. not charging as there’s not 12V on the exciter) or is it "being told to charge" and failing so is also in need of replacement?
I know the battery is in need of replacement (I have bought the replacement) and I know the alternator isn’t charging the battery (for whatever reason). I know I’m getting no information on the quality of the various connections, as there’s no charge (current) coming out of the alternator, I can (and will) do this later when the fault(s) are fixed.
When I test the voltage on the excitation terminal of the alternator (thin yellow & brown wire into the back of the alternator) it’s showing 6.23V to ground (either battery or alternator). This strikes me as odd, I was expecting 12V, but then again it’s not 0V so it’s clearly not a blown fuse, etc. What should be on this terminal?
I’m currently working away from home, and so don’t have the battery here to fit (it’s arrived at home since I left, and has had the charge topped up since it arrived). I can get it couriered up here but if I also need to do the alternator and it won’t get me home, it’s not worth it, I’ll just get the car towed home…

1. Engine off, all accessories on for 30 seconds, then off. What voltage __11.8V__
2. Voltage across battery at idle (no electrical load) __11.8V__
3. Voltage across battery at 2000rpm (no electrical load) __11.8V__
4. Voltage across battery at 2000rpm (everything electrical switched on) __didn't do, see below__
5. Voltage at ALTERNATOR at 2000rpm (everything switched on)__as above but 11.8V without electrical load__
6. Voltage drop between alternator body and battery negative (YES negative). Measure at max electrical load and 2000rpm __<10mV__ (millivolts please)
7. Voltage drop between alternator positive and battery positive. 2000rpm, max electrical load __<10mV__
8. Check Voltage drop from Battery Negative terminal to 1st groundpoint on vehicle__<10mV__
9. Check voltage drop from 1st ground point to block__<10mV__
10. Check voltage drop from Alternator Housing to block__<10mV__
11. Voltage from alternator positive to alternator housing__11.8V__

What are your symptoms
The normal for failing battery, from what I've been reading: Gearbox fault, traction failure, speedo and tacho flicking to zero particularly when braking, relays switching on & off behind the dash, etc. I know the battery is on the way out, and the alternator isn’t charging. Today the suspension failed to pump up, so I can’t get home to fit the new battery. Question is whether the alternator needs replacing or whether the excitation isn’t working right…
What have you done to fix it so far
Electrical sticky, asking for advice before I get more parts as I think it might not be a faulty alternator, but the excitation not working (but I don’t know how to check / bypass it).
As some history: The gearbox fault went on a few years back, due to the BECM not going to sleep. After tracking down why (there’s something in the neighbourhood that’s keeping it awake) and replacing the battery, the simplest solution to stop it happening again was to put a 50W solar charger (with decent regulator, etc) on the battery. It stays awake overnight, but charges up the next day. I think this is why I’ve not spotted the alternator failure – I don’t use the car enough to have a problem show up… (Normal commute is by motorbike.) The solar wasn’t on when the sticky testing was done.

Thanks in advance,
 

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you can run for about 1.5 to 2 hours on a good strong battery , car runs at about 40 amps at idle I think . unplug all the electricals that you don't need , fans etc , pull relays this will help, may be replace the regulator in the alternator , this might be your problem? . with the rf interference may be unplug the booster unit in the back , you will have to be closer to the car to unlock it .
 

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I drove my rangie with a blown alternator for approximately 50 miles to get me home, the end of the journey it didn’t like changing gear , I dared to put an indicator on, but I got home.
replaced the brushes in the regulator for a fiver, you can buy regulators cheaply, but the originals are better than a lot of copies out there.
as for solar chargers, I’ve yet to find one that doesn’t take more power than it puts in !
 

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Discussion Starter #4
Thanks for this, looks like I should get home and can then sort the causes out :)
I did try unplugging the booster unit a while back, but like to have the remote and the solar had been working until a few weeks back (and how much I use the car changed). I think I need to revisit that decision...
 

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You don't need to completely unplug the fob receiver, just unplug the single blue wire that goes to the aerial. That will allow it to still work but will reduce the sensitivity so you need to be closer to the car for it to work. That should be enough to stop it responding to other signals and allow the BeCM to go to sleep.
 

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Discussion Starter #6
Gents, thank-you. New battery and non-functioning alternator got me home - first errors (gearbox, traction, etc) at around 45 minutes, but still running after 75 minutes when I arrived home. Phew, now the car is where the tools are...

Now to find the root cause: If anyone can measure the voltage on their exciter wire I'd much appreciate it (thinner yellow & brown wire, I think this might be marker D+ on the back of the alternator but can't see to check). Mine is 6.23V DC (between the terminal and the alternator body and/or battery earth terminal - as the alternator isn't working they're the same). That strikes me as unusual on a 12V system, but I can't find what is should be anywhere... I believe if it's not right, the alternator won't work...

Thanks,

AW
 
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