I've had a few posts on this car in the past about similar issues. what I first suspected was a bad OVP, replaced with new OVP...still blew the fuse...had a hot convenience relay on all the time....found broken wires for convenience lights both rear doors and broken wires for rear windows in both door pillars between front and rear doors. repairs all wire breaks that I found..this solved my hot convenience relay all the time..and I hoped my parasitic battery drain... bought new battery and new alternator...still have the classic OVP problem...no electric idle control, etc, etc, my charge back to the battery at idle is 13 but at higher RPMs goers up to 13.45...also replaced ECM....the idiot light for the battery on the dash lights on start up so I know the alternator is grounded base don other threads here.

deactivated alarm. checked all ground locations...replaced tranny to frame ground strap with a larger copper wire

To me I still have a bad ground somewhere, but where....I isolated every component that the K1 energizes and as soon as I turn the key to position 2, the OVP fuse blows. Also went fuse by fuse in the fuse panel and still kept blowing the OVP fuse. I'm about to rip my hair out....any suggestions on the car...I already know how to rip my hair out.

new components are radio and A/c compressor but I've isolated them as well during all my other isolation above..no luck...

Also replaced the headlamp switch...

Today cold as a witch's thorax and the battery was kaput.....need some good suggestions, thanks.

On my 1983 W126 at K2, components in play are the battery, glow plug relay, starter, ignition switch and neutral safety switch and their associated wiring.

I'd start troubleshooting by disconnecting the battery and cleaning each and every connection to those components with a good electric contact cleaner.



Don't forget to inspect the battery cables for corrosion under the insulation. Sometimes simply changing both battery cables cures electrical system woes.
Heavier duty (thicker) marine grade cables are a good upgrade that are readily available at most boating supply stores.


If the connections are cleaned and the problem persists, I'd suspect the relays and the ignition switch of having failed.

The contacts will fail (just like points on old gasser ignition systems) after so many cycles. The contact surfaces get pitted after a lot of use.



Less likely are problems with the starter and starter solenoid as they are quite robust units.

Good luck, hopefully I've been helpful.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

13v at idle and 13.43 at increased rpm sounds good.

__________________

Gone to the dark side

- Jeff

Have you used a DVM to measure for slight voltage drops from ground to ground? Anywhere you have a bad ground you should be able to see a difference in voltage. Measure from body ground to engine, alternator to engine and body and so on. You might see a difference which would indicate a ground problem.

Hope this helps.

Even though the alternator charges up to 13.45, if the car sits for a day or 2 whatever parasitic drain I have depletes the battery and the car won't start... this is a brand new Duralast platinum with the highest reserve I could get...

I replaced the ignition cylinder too, but that's just the keyed portion of the ignition switch, I wouldn't think that could cause a problem...

Okay that is different. It sounds like you have a short somewhere.

Use an ammeter between a disconnected battery terminal and the battery post. If it draws more than a few tenths of a volt, start disconnecting fuses one at a time until the ammeter shows little or no current. When the current goes down the last fuse disconnected is the offending circuit. If there is still current draw after all fuses are removed, dscon ect things until it goes away. Things like the alternator, and other non fused items is where you go then.

Hope this helps.

thank you