A bad NSS, and a bad electrical portion of the ignition switch are possible causes.

Another thought, the glow plug relay may also be stuck.
Try unplugging the glow plug harnesses from the relay.

Remember that more than one component might be defective.

EDIT: also make sure the short braided cable from the stater motor to the solenoid does not contact the starter motor case. BTDT.

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

I put a push button on between + on bat and small screw on starter it worked all the time. I later found a broken wire near nss

S


Since bridging the solenoid activating terminal to the main starter feed works. You have isolated the issue to low voltage to the starter solenoid.

Measure what is reaching the solenoid terminal. With the key in the starter engaging position of course.

Various ways to find the source of the voltage drop. On that feed. Even a low voltage light bulb with two leads perhaps. Or just keep tracing the voltage back to the source for the high resistance point.

As stated many have resorted to using the ford solenoid as the situation persisted. Even after the starter was rebuilt. The though given to the wire size etc on perhaps many German cars was not the greatest. For that circuit.

For example the rebuilt starters may have a poor aftermarket new solenoid that just demands more to activate. This is not a complex car. I stay away from chain store items on the more modern complex cars for several reasons. The aftermarket parts are worse than just hit and miss. Far too many only work for a very short time as well. The chain stores unless something has changed look for the lowest price provider for what they sell. Some may have been burnt so bad they have stopped this practice. I just do not follow things all that well. Since I reduced activity.

I’m going to try this out tomorrow. Didn’t think about the short braided wire. Still find it interesting how I made an overlay from the ignition switch to the solenoid, bypassing the NSS and what not, and it still couldn’t get through.

Time to break out the DMM. Will come back with results. I just find it so odd since I overlaid the wire from the ignition switch to the solenoid, bypassing everything in between. And the main battery cables are brand new so I know those are fine and the battery is in good condition

I had the same problem several months ago (82 240D), sometimes it would start strong, other times it would click, and all electrical would drop off to nothing.. it was driving me crazy.

So one day I was wiggling the wire harness going to the solenoid while my girl sat in the car, she said things lit up when I was moving the wires. I stripped back the wire headed to the back of the alternator to look for problems.. nothing was compromised. I pulled the wire off and cleaned everything up, still not knowing what was wrong, there was no problem with connections or the wire itself as far as I could tell..

Long story short, the car has been starting fine since then, it's being driven daily now and the unknown issue has yet to return..

Hope this helps

See the attached picture. To disconnect the Glow Plug Relay entirely you need to un plug the square connector and remove the wire under the Nut where I have the red + sign.
That wire is always connected to the battery.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel