What can kill alternators?

[Shaun @ Tru6]

The engine wiring harness on my 94 E320 biodegraded and with it, all the dash lights were on and the alternator wasn't charging but oddly enough, it ran fine otherwise. I put a newer used harness in from 2004, it was in great shape, no drama on connections and laying it in. Car started right up and ran perfectly.

But all the dash lights are still on. And I just tested the alternator and it's junk. Easy to get another and put it in but don't want some other mysterious wiring issue to fry the new one.

What kind of wiring problems can kill an alternator?

[KNS]

Check all your grounds.

Was it "factory rebuilt"? They've been known to be junk right out of the box.

[Shaun @ Tru6]

I'm sorry, I should have been more clear. The alternator in the car is original to it. I'm getting a new one tomorrow. With all of the dash lights on, I don't want some other issue to fry the new alternator.

[vash]

i've killed every alternator by using it to charge up a dead battery.

sometimes you cant help it, but i am really aware of it. if i can, i charge my battery first.

[Shaun @ Tru6]

Battery is new Cliff but I did run it down to 0 when the engine wiring harness went. I charged it and it's at 11.5V now.

[Nostril Cheese]

Its a W210. There's your problem.

Seriously though, check grounds.

[Shaun @ Tru6]

It's a W124. Have had 2 others, awesome, well built cars that are a joy to work on. The original wiring harness is a known issue though.

Will check all grounds too, thanks.

[fastfredracing]

Are all your dash lights still on? Just the batt/charging light, or all the warning lights? The alt may not even be bad, maybe there is a problem in the field current, or still an open or short somewhere in the harness, or some collateral damage you missed ?

[Shaun @ Tru6]

Hey Fred. Every single light you can imagine is on. That wouldn't be uncommon for a bad engine harness but the new one went in great and I double checked every connection. And as a 2004 used harness, it should be fine. The one I got looked pretty much brand new. I have sent a note to the seller though.

I pulled the passenger footboard off and there's no visible damage to the computer there. Saturday I'm going to pull the fuse box in the engine compartment and look underneath.

[Nostril Cheese]

Originally Posted by Shaun @ Tru6

It's a W124. Have had 2 others, awesome, well built cars that are a joy to work on. The original wiring harness is a known issue though.

Will check all grounds too, thanks.

One of the last good ones. I've dealt with those stupid harnesses more times then I wanted too.

[Shaun @ Tru6]

I'll be posting a thread soon on 2015 Volvo S60 T5 vs 94 E30 vs 01 Volvo S60 2.4T vs Ford Focus vs. 15 Velocathing. Just driving impressions. The E320 is soft but a close second to the 15 Volvo.

[Nostril Cheese]

I love my T5 C30.

[ckelly78z]

The thing I have found about alternators is to have them rebuilt by a specialist rather than to trust the junk that comes from an autoparts store. A specialist stands behind his work, uses better componentry, and generally doesn't cost much more in the rebuild, while autoparts stores use some third world sweat shop for the rebuilds, and the cheapest components they can get.

[targa911S]

^^^^ Agreed^^^^ just had the one on my MGB done. Better than new now.

[pksystems]

Too much heat can kill them.

[Mrmerlin]

from the info provided,
it sounds like the alternator isnt charging thus all of the warning lamps are on.

The easy thing is to pull the regulator and check the brushes,
swap in a new Bosch regulator if they are worn..

NOTE nominal battery voltage should be 12.5V if your reading is only 11.5v,
then you may have a bad cell and this could kill an alternator. Recharge it and test it ,
if no good then replace the battery.

As previously posted the alternator isnt made for battery recharging.
Same goes for a battery maintainer this isnt a way to recharge the battery

If you have a low battery then charge it with a 4 to 6 amp charger for a few hours.

The other way to kill the alternator is to jump start with a battery boost charger, or another car
this can spike the diodes thus reducing the output of the alternator,

NOTE when its charging at 1500 rpm you should see from 13.6 to 14.2v with the headlights on.

NOTE make sure the belt is tight, the highest load on the charging system is just after you start the engine

[304065]

Shaun, if it's only 11 volts, charge it for three days until it shows 12.5. Get a load tester, knock off the surface charge, then test it again to be sure it's really at 12.5.

As Cliff says (and as I have been saying for a decade about 911 alternators) using the alternator to charge a dead battery will kill it because the diodes overheat. Always favor a stationary charger over the alternator following electrical issues.

The last thing is the ground-- make sure the grounds are very solid-- if the alternator can't get a ground, it will try to make one-- through the bracket, through the insulation, through the belt-- these things will royally screw it up.

[Shaun @ Tru6]

Thanks Guys. Yeah, I took it off the charger early to test the harness. Anyway, my dumb question had more to do with potential problems with the wiring harness outside of the engine harness. Folks on Benzworld confirmed the alternator harness was outside of the engine harness. Better, the dash lights are all on because of the alternator being 100% toast. They also recommended changing the over voltage protection relay. So, tomorrow with a new relay and alternator, and the battery trickle charging now, and checking all grounds, I should be all set.

Building the powder coating booth, 928 motor and the business, I need to minimize drama these days.

[Shaun @ Tru6]

With the battery at 12.7V, got the alternator and OVP in, car started right up with no dash lights on and running smooth as silk, alternator putting out 14.29V.

I just absolutely love this car. Want to put a Sportline suspension on it but have enough projects for now.