New alternator while and instrument light weirdness

[IamWedgend]

Hi all,

This is on a 280i - Recently swapped out my old alternator for a shiny new 75amp that looks exactly like the old one. Link below
However, with the new alternator in, the car has developed a high pitched whining. It increases with revs, but it disappears when the plug is taken out of the back of the alternator, so I assume its an issue with some of the internal electrics in the alternator and not the bearings?

Additionally, some of the other electricals have started behaving weirdly - right indicator flashing at double speed and battery warning light failing to come on. To be fair, it was unbelievably foggy and damp when I took the car out, so it's possible those issues were just condensation - but the timing makes me think that the alternator is putting out dodgy power.

Anyone had experience with this?

Alternator: https://www.ebay.co.uk/itm/324193342893?ul_noapp=t...

Edited by IamWedgend on Friday 27th November 11:09

[Penelope Stopit]

To begin with diagnosing the problem, concentrate on the no battery warning light fault, if there being no battery warning light is due to a faulty alternator there's no point in being bothered about the whine as the alternator will need to be replaced



The brown/yellow cable that connects to the small alternator plug terminal is the battery warning light cable (yes , you very likely know this but....)

With alternator connected, switch on ignition, check there is no battery warning light illuminated

Now unplug the alternator and use a short length of cable to connect the brown/yellow cable at the small plug terminal to the alternator body, the battery light should now be fully illuminated

If battery light is fully illuminated when connecting the brown/yellow cable at the small plug terminal to the alternator body and isn't illuminated when the alternator is connected up, alternator is faulty

If the above isn't the case, post back

[Penelope Stopit]

Indicators flashing quickly on one side is often caused by bad connections at the lamps or a blown bulb

[IamWedgend]

Thanks for the advice!

Interestingly there is no cable for the smaller plug on my machine, just the three pronged bigger plug. There never has been, as far as I can tell, and the battery warning light seems to have worked fine up till now.

Re the indicators, the indicators seem to be working, but are themselves flashing twice as fast. Very odd.

Edited by IamWedgend on Friday 27th November 12:13

[Penelope Stopit]

Am confused now, thought that your earlier topic pointed to there being a warning light in the circuit
https://www.pistonheads.com/gassing/topic.asp?h=0&...

[IamWedgend]

Yea i'm confused too to be honest. The warning light has generally worked (bar that topic), but there has never been a separate cable going into the back of the alternator, it's just two wires wired into the larger three pronged cable. I assumed the warning light was hooked up to that, or perhaps to another part of the system?

[Penelope Stopit]

If all is good with the indicator lamps wiring/connections and the correct bulbs are fitted, 21 Watt front and back and 5 watt for side repeater

An incorrect flasher unit will flash quicker than it should.

Flasher unit needs to be 2 x 21 Watt + 5 Watt and those figures should be stamped on its case


Alternator overcharging will also cause flashers to flash too quickly and also blow other bulbs (voltage too high)

[Penelope Stopit]

IamWedgend said:

Yea i'm confused too to be honest. The warning light has generally worked (bar that topic), but there has never been a separate cable going into the back of the alternator, it's just two wires wired into the larger three pronged cable. I assumed the warning light was hooked up to that, or perhaps to another part of the system?

Mmmm

Will be worth working back along the loom from the alternator plug and finding the brown/yellow cable, the alternator needs the warning light current draw to cut in at low engine revs

Could be a problem in the engine loom or behind the instrument cluster, find the brown/yellow cable first

The battery light shouldn't be illuminating at any time if it's not connected to the alternator

Brown/yellow could be rubbing on the engine somewhere or man made fault

Has someone connected the battery light brown/yellow cable to the oil pressure switch or something else?

Best to get to the bottom of the missing alternator brown/yellow problem first

[IamWedgend]

Alright i'll pop out and have a dig into the missing lead!

Is it possible this could all be caused by a failed regulator diode? Apparently it makes the whining noise, and might be responsible for giving out the wrong voltage and blowing bulbs/ overcharging the indicators.

Edited by IamWedgend on Friday 27th November 13:12

[Penelope Stopit]

Faulty voltage regulator causing overcharging could create a whine

Faulty stator or diodes could create a whine

Bad alternator design could create a whine

You could run the engine and get the revs up to 3000 RPM to be sure the alternator has cut-in and then measure the voltage at the battery while increasing the revs, voltage should be 14 to 14.5 volts

Doesn't alter anything with the brown/yellow cable though, still needs sorting

[IamWedgend]

Hi Penelope,

Thanks once again for your sterling advice.

I conducted an investigation this lunch time. As I've photographed below it appears that the brown and yellow wire goes straight into the back of the alternator vial the big, three prong plug. I took the whole plug out, gave it a wipe and a wiggle and the battery warning light came back on.
I've included a picture of the back of the alternator. I know the back of the plug is missing - getting a new one this weekend.

I also tracked down the indicator issue - the back left IS not working - my friend I asked to check it while i was in the cab was apparently confused. I'll dig in there and see what's happened - whether it's blown or just come loose.

[Penelope Stopit]

Great, cable is there after all

The possible bad news is that it looks like the main positive terminal has been overheating


A common fault with your cars type of alternator/plug set-up is that the main positive terminals of the alternator and plug do overheat if only one positive cable is used to supply the alternator

I take it that you're getting a whole new plug and clip as well as the cap that comes with it, new terminals come with the plug

You or someone needs to rewire the alternator

Use 2 new lengths of this thin wall cable (standard PVC cable is too big for the plugs)



found here https://www.autoelectricsupplies.co.uk/product/70/...

Run the new cables back to wherever the original brown cable connects up to (but do get rid of the original)

Also cut back the brown/yellow warning light cable to where found good and not brittle, solder in a new length of brown/yellow from this good point all the way to the alternator plug



What you should be aiming at ending up with is



plugged into the back of the alternator

More bad news is that there is a good chance that the positive terminal of the new alternator is burnt, it might clean up if it is. If the positive terminal of the alternator is burnt real bad, a new rectifier (diode pack) is the cheapest solution, the alternator positive terminal is part of the rectifier

Rectifier similar to this but with spade terminals



The thing is, the alternator might be faulty and a burnt terminal will void any warranty

[IamWedgend]

Thanks Penelope, really useful.

Will get it rewired as suggested. Do you think replacing the plug and rewiring could solve the above mentioned issue if the positive terminal isn't burned? I'll take it in to my local who can measure the voltage and check the alternator out as soon as it's rewired. Cheers!

Best,
J

[Penelope Stopit]

No, I doubt very much that rewiring the alternator will stop the noise (there's always a first time though), with a little luck the alternator positive spade terminal that is part of the rectifier will not be damaged and you can return it for an exchange under warranty

The thing is, there is the possibility that an overheating positive terminal is the cause of alternator failure

[IamWedgend]

Right, gotcha. Worst case scenario it's another 50 quid for an alternator, which is not going to kill me. I'll keep you posted - thanks again.

Where did you get your vast store of auto-electrical knowledge from?

[Penelope Stopit]

Ok then, hope your'e lucky and get away with a warranty

Have worked at, in, with and amongst automotive electrical for many years, it's my job

British cars were the first ones that I got my hands on, all wired to British Colour codes like your wedge is

Cheers

[IamWedgend]

Fingers crossed!

Ah great! I know you're not supposed to offer professional services here, but do you still work in the industry? If i'm struggling to get it sorted after the re-wire and new alternator I might need a pro like you to look at it.

Cheers!
J

[Penelope Stopit]

Sorry about not being able to help, the flight back to the UK would kill the job

Any good auto electrician will sort it, best using someone that's been in the trade for many years

[KKson]

Hi Penelope was it Cyprus you're at? Sister lives in Pissouri so will be heading over at some point again when Covid is defeated. Hope all is well. Cheers

[adam quantrill]

Those crimp terminals are vulnerable to damp penetration. Even when crimped properly with the correct tool (so you get a cold weld to the copper) over the years you'll get corrosion penetrating, once there's enough damage the resistance builds up and it starts to overheat.

I'd recommend crimping and soldering these things, the solder will keep the moisture out and also adds a little more conductivity to the equation. Before putting the terminal on, put on some loose heatshrink and push it well away from the soldering, in case you melt the insulation a bit, then you can heatshrink it afterwards.