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.