W115 - Bypassed Glow Circuit, Battery Dead?
 

Well, not sure what happened . . . . Bypassed glow circuit on my '75 300D and wired in a Ford type starter solenoid with manual push button glow (finger on button controls length of glow cycle) followed directions exactly and car fired immediately. Next morning, battery drained completely? What happened? Could it be a defective solenoid? Can you actually wire this wrong by using the wrong poles (two large poles) My understanding is that the two large poles are identical and it does not matter which pole is wired direct to positive battery post. Any thoughts on this?

Is the original relay still in the system? It failed right, after working a few times? I'd suspect something in that original relay is draining the system.

Yes Kerry, system worked great a few times and died! Which then prompted the manual set up -so orig relay fried, yes? I do have a back up relay for testing purposes . . . . back to the drawing board -

Is the original failed relay still wired into the system or not?

Yes, if I unplug the harness from the original relay will the manual system still work? My understanding was that it remained plugged in - desulphating battery right now as it was drained overnight completely -

I don't know. It depends on how you wired in the manual system. My hypothesis is that the problem lies in that relay.

ran a new 8awg wire from solenoid to number 5 glowplug (disconnected orig power wire by firewall and ground by number 1 glow) ran another 8 gauge wire from the other side of solenoid to positive post on battery (fused with an 80 amp strip fuse)) ran a small wire from center S post on solenoid to starter button and another back to Solenoid post . . . original relay still wired in - I suppose I could disconnect orig relay and see what happens when I engage button . . .

use a 12v light bulb, hook it between the neg ground & car ground, if light on bright , then u have a serious short.
Or else u find a way of boosting her every morn.
My 300sd I just on hook batt when I park her over night!

was just thinking about this again -the original power lead off the firewall was disconnected and taped back as I ran a direct lead from positive post to number five glow plug . . . . now, even more confused!

Well, isn't that the source of the battery drain then?

Weird, the instructions I was working with said to disconnect the original power lead at glow plug five . . . . so do I now reconnect the factory power at number five in addition to the new lead coming off the battery? Pretty dense when it comes to electrical circuits and how they actually work -thanks Kerry!

If there's a power lead coming from the battery to plug 5, it's going to energize that plug all the time, drawing down the battery. Even if the original relay is disonnected from the plugs, it's still getting power from somewherre and a problem in it could be drawing down the battery. Just to be clear--there's a direct wire coming from the positive post of the battery with no interruption, to glowplug 5?

correction: wire from one pole on starter relay to number five gp. The opposite pole on relay runs to positive post on battery. Make sense?

If it were me, I would disconnect the original relay completely from the wiring. I would run a heavy gauge fused wire from the positive post to the new solenoid and another heavy gauge wire to plug 5. I would then run the wire for the momentary switch from the solenoid into the cabin and back. This would make for a completely new independent circuit with the problematic original relay out of the question.

Yes. So just disconnect the original relay and see if that solves the problem. It was a known fault inthe system before you circumvented it.