280sl goes through alternators

[ctaylor738]

Good morning,

A month or so ago, 280sl not charging the battery.  I put in a rebuilt alternator that my meticulous friend Ray bought “a while” ago but never installed.  It failed immediately.  I put in another rebuilt from Adsit along with a new voltage regulator.  I used Adsit because they were the only vendor with an AL64x unit taking the 3-pin connector. Now the car is back with the light on and no charging.  I swapped out the new regulator, no change.  I checked the wiring and it seems OK.  Is it just bad luck, or am I missing something?

Aargh!

CT

[clunker]

Well three dud alternators and two VRs do point to something else.

I am sure you have gone through the wiring carefully, but just in case do check the exciter circuit which runs through the D+ line on the VR to the charge light on the dash. That exciter circuit (which fires the electromagnets to kick start the alternator) I believe has to have a 72ohm resistance (obtained via the dash incandescent bulb or a parallel 82 ohm resistor if you replaced with LED bulb), and if that shorted or incorrect maybe a source of issues.

In any case perhaps this service guide for the Bosch alternators might be helpful. Good luck.

PS also - and this a long shot though I have seen it - check that the connector to the bottom of the VR is correct. The connector is labeled, and should be orange to DF, black to D- and two red-blue wires into D+. If wrong, then a PO maybe just switched the pins at the alternator end to fix it - you might have missed that. It easy to use a pick to fix the VR end connector. If say the DF and D- switched, the circuit may have sort of worked in the past until the (mechanical) VR failed, a new solid-state VR may be not so forgiving.

[mdsalemi]

I used Adsit because they were the only vendor with an AL64x unit taking the 3-pin connector.

Chuck, Adsit is, well, Adsit. I won't go any further there.

Has the alternator been bench tested? Maybe the rebuilt isn't working. Surely there is an auto electric place you can go to have them tested without going through the process of installing on the car.

Most of our vendors known to all (Pelican Parts, Autohaus AZ, even Rock Auto and--of all things--your local O'Reilly) seem to have the AL64X and the photo shown on all of them that I saw is with the 3-pin connector. That's the 35A alternator, yes? The one thing impossible to determine is if the reman is Bosch or a third party. The unit is Bosch for certain, but who does the reman?

All seem to be out of stock at the moment but at least one said back in stock on November 25.

[ctaylor738]

Thanks for the suggestions.  With the door open and the ignition on, the charging light and the door ajar light look exactly the same.  And when Alternator #3 was working, the alternator light came on and went off just like you would expect. 

I measured continuity on all of the wires and they all start and end correctly.

There do not appear to be any 3-pin alternators available from any of the reputable sources.  After the way Adsit has treated and is treating me, they are off my list of vendors.

So in near-desperation, I just received a Bosch-rebuilt AL74X from the local dealer, and I will rewire the cars harness to accommodate the spade wiring.  So stay turned.

Thanks for the link to the Bosch documentation.

Cheers,

CT