I just picked up a 1990 W350 yesterday. It won't start with the key. They unplugged the 2-pole plug coming off the battery that goes to the starter motor and are using a jumper wire in the plug to start the motor.

Any ideas on what went wrong that they had to do this? I'm guessing something either in the ignition switch itself or the starter relay. Being that this is my first 1st gen I don't even know where the starter relay is.

Any ideas would be appreciated. Thanks.

 

It was the ignition switch in mine, but it also let to a faulty fusible link that blew consequentially from the switch shorting. Look on the + terminal of your battery and trace down the 6 gauge black wire until you come to a block with 5 or 6 wires coming in (and one from the alternator coming in). Gently pull on them, and if any stretch, they are gone. THese are your fuseable links. I had a few gone, and a haywire mess of previous owners messing with mine, so I rewired my whole block according to the Factory Service Manual and used Maxi Fuse blocks instead.

Look through the sticky and there is a plenum of information in all sections, neatly categorized (welcome to 1st gen!).

Another issue may be the neutral safety switch. Its on the side of the tranny, driver side not far from the shift linkage. You can test it with a multi meter while someone clicks back and forth between drive and neutral. I'm pretty sure it's supposed to have continuity in Park and Neutral, but closed in Drive or Reverse.

Keep us informed, several of us have been there

 

I haven't done much looking at it yet as I just picked it up last night. I'll take a look at those wires and the neutral switch. I did see one fusible link that looked like it'd been replaced once.

I've been going through the sticky slowly, but I hadn't seen anything on this. Maybe I missed it, I don't know. I'll check those things out tomorrow probably since it's already dark and the 06 is takin up the shop right now.

 

Well, I haven't had much time to work on this, but I did figure out what's wrong. There's a couple fusible links blown, going to rewire the whole thing with fuses.

The big thing though is there's no wiring to the neutral switch. I had a heck of a time finding it since it's covered in grime and there's no wires plugged in. Definitely explains why it won't start with the key since it isn't grounded and why my reverse lights don't work. Now I gotta figure out where the wires come from and where they went, since there's nothing down there. I did jump a ground wire from the ground on the starter relay to a chassis ground for now and it starts right up with the key, but I would like to fix it right.

Can someone tell me where the wiring for the neutral switch ties in to the main harness? I can trace it back, but I'd have to unwrap the whole harness to do it.