Chicken Drumstick Posted August 12, 2023 Share Posted August 12, 2023 What sort of voltage should I see on the different terminals on the alternator? 200Tdi. There are 3 terminals. Big brown wire (B+) I'm seeing battery voltage, circa 12.5v either with the engine running or without. The white wire is I think the W terminal for rev counter, I don't have a rev counter, but it is wired into the loom. I'm seeing no voltage here running or not. Small brown and yellow wire. Is this the exciter wire? Again seeing no voltage here engine running or not. Engine starts and runs, but I'm not seeing any charge voltage at the battery. I'm guessing it is a fault with the alternator, but wanted to check as the original alternator seems to have failed and caused a short so that with the engine running I was reading 7-8 volts at the battery, but normal voltage when not running. Have swapped on this spare alternator that came of a running vehicle. Not seeing the weird low voltage now, but also still no charging and trying to narrow down on if I should buy a new alternator or mess with the wiring further. Thanks. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted August 12, 2023 Share Posted August 12, 2023 Bring the revs up a bit and see if you get greater than 12.5V on the brown wire, if so then the exciter wire, which should have a small current flowing in it is not exciting it and needs the revs to get going. If it doesn't, then that alternator is kippered as well. Quote Link to comment Share on other sites More sharing options...
miketomcat Posted August 12, 2023 Share Posted August 12, 2023 Check the bulb in the ignition light if that's blown the exciter wire has no voltage so doesn't wake the alternator up. You should be seeing up round 14v when running. Mike 2 Quote Link to comment Share on other sites More sharing options...
Chicken Drumstick Posted August 12, 2023 Author Share Posted August 12, 2023 Thanks, so since fitting this alternator the alternator dash light comes on and stays on with the engine running. Change in revs is making no difference. Assume the consensus is a new alternator required? Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted August 12, 2023 Share Posted August 12, 2023 Yep, most likely. 1 Quote Link to comment Share on other sites More sharing options...
fmmv Posted August 12, 2023 Share Posted August 12, 2023 Maybe just a regulator/brushes pack 1 Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted August 12, 2023 Share Posted August 12, 2023 Yes, change the brush pack first. They’re cheap enough and it’s worth a go. I swapped the one on mine recently and it solved a problem with low charge voltage - the brushes were just worn down. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 14, 2023 Share Posted August 14, 2023 In addition to the other comments - those frayed wires into the crimps can't be helping future reliability either Quote Link to comment Share on other sites More sharing options...
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