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Old 01-12-2015, 12:31 PM
Alec300SD Alec300SD is online now
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Join Date: Nov 2013
Location: San Mateo, CA
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DIY - AL129X alternator in a 1978 W116 300SD, continued...

Testing new alternator: With all the wires connected to the alternator, I temporarily connected the battery and took voltage readings with the car off and then while running. I got -12.63 volts with the car off and with the car running I got -14.40 volts. So I shut of the car, disconnected the battery re-installed the battery tray and battery and checked the battery voltage closely over the next few days.

I panicked when the glowplug light failed to illuminate on startup, I thought I created an improper circuit. I disconncected the new 6 gauge power connection (red wire) and retested the glowplug light. It still would not light up, I figured the bulb decided to burn out at that exact moment when I replaced the alternator. (It ending up being worn contacts in the ignition switch, as yesterday I could get the glowpug light to illuminate by jiggling the key in the number two position.)

At idle, with heavy load, the voltage doesn’t dip below -14.00 volts and the battery voltage stays a stable -12.77 volts when the car sits overnight. No troubles with charging or voltage for the past 9 days. Yay!

‘Desert Rose” is back in service as a dependable daily driver and she is ready for new lighting options and a new ignition switch.
Attached Thumbnails
DIY - AL129X alternator in a 1978 W116 300SD-terminal-connection-new-b-power-wire.jpg   DIY - AL129X alternator in a 1978 W116 300SD-new-routing-alternator-wiring.jpg   DIY - AL129X alternator in a 1978 W116 300SD-voltage-rest-before-running-new-alternator.jpg   DIY - AL129X alternator in a 1978 W116 300SD-good-charging-voltage-first-time-running-car-new-alternator.jpg  
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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022
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