Chuck:

Arthur is correct. You need 9Volts to fire the optical trigger. If the coil you are using HAS internal resistance (check via Arthur's method) then you DO NOT want to use the external resistance. If the coil does not have internal resistance, then you use the external. As he also suggested, cleaning the optical unit is a good idea.

I have run both the original Bosch coil and a Crane aftermarket (currently installed) and both worked fine. I do understand that they have updated the system (I think the yellow coil(-) is the updated system which is the one I have) and made some changes in the control unit and optical window disks. When I used the Bosch coil I went from the .4ohm resostor to the .6ohm resistor to coil (+). The Crane coil came with its own resistor so I wired from the ignition point on the .4ohm resistor to the crane resistor thus bypassing the originals.

At $100 (max) per unit I might just spring for a new one just to get the updated electronics and eliminate any problems that may have been caused by the PO installation or whatever.

I am not sure about your voltage reading from your pre-resistor. I have the MB service manual on the stock ignition and it has the test voltages at all points, I will check it when I go home at lunch and post the test figures. Might be a problem in the resistors..

Dan

[Edited by DANTRCAV on 03-22-2001 at 08:13 AM]

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Dan Taylor/ Tulsa, OK MBCA
'84 300D/'90 Jaguar XJ6/XJ40