I was poking around under the hood yesterday after replacing the alternator and noticed a solid dark green wire sticking out of the harness branch that plugs into the "BLACK" ECM port. I don't see anywhere in the plug where this wire could connect, there's no broken wire sticking out of it, and there's already a solid dark green wire connected to port #4 (see figure 2). Is this normal, or do I have a problem?

Figure 1. The plug that connects to the "Black" port.



Figure 2. The Yellow arrow points to the connected sold green wire. The White arrow points to the orphan.

 

It goes to pin #11. Does your DLC port work (OBD scanner)?

George

 

>>>Does your DLC port work (OBD scanner)?<<<

Well, I think so. I just got the car out of a service garage where I had a bunch of routine maintenance done, and they told me, after they had trouble starting it, that the tech pulled code B1480. They described that code as, "battery random protect circuit fault – alternator not charging". I think that was a typo and they meant to say "battery rundown". I don't think that code has anything to do with the alternator, although it was found to only be charging 13.2V.

After your reply, I took a closer look at that plug and see that either the factory screwed up royally, or somebody messed with it in the past. See pic below.
Have you ever worked on these things? Do you know how to get that cover off? If I can get that pin in #11 out, I'm fairly confident I can fix this.

Thanks for your help, George.

 

I have never depend one of our ECM connectors, but they make a variety of tools. Where are you insert this thin blade and it depresses that catch on the pin so you can pull it out backwards in the direction of the wire. You can find us on YouTube. What I find curious is that you can read your codes because that’s the class to serial data lying to the ECM so I wonder if there’s a wiring hack somewhere else. I’m not in front of my computer right now but when I get back I’ll look and see if there’s another class to date a line connection to the ECM besides C4 pin 11 which is what we’re talking about. In theory you should be having all kinds of operational problems with that wire disconnected.

George

 

I'm not having any operational problems. In fact it runs and drives amazingly well - and everything works as far as I know. The only problem I am having is the interior lights won't go out. They worked fine, including the timed automatic shutoff, until I picked it up from that service garage. They did something. I sent them an email asking about it. But, of course, no reply.

 

I just ordered a 100 piece terminal extractor kit from ebay. Laughably cheap & Chinese.
If it works for this one job it'll be worth the money easily.

I still don't know how to get that cover off without breaking it.

AFTER THINKING ABOUT IT ... I'm wondering now If I should even try to fix it. I'm worried the other end of that wire might be grounded, or connected to something that could damage the ECU. Where does it normally go? Any idea how to test it?

 

I took a more detailed look at this. There are 2 class 2 data line pins at the ECM. The other one goes to the BCM which itself then connects to the class 2 bus for the entire truck. That second pass through connection must be adequate for communication throughout the truck. It doesn't sound like you are having any issues and I can see evidence of a hack at the connector so who knows what else has been done. Unless you develop an issue I would leave it as it is.

To answer your question that orphan line goes to the class 2 connection comb under the left side of the dash.

George

 

Thanks George. I got a little squeamish thinking about connecting that wire and having it toast my ECM. The car was already 22 years old when I bought it, so who knows what its history is. However, I would like to remove that cap and tuck that white plastic whatsis back under where it belongs. If you have any idea how to unlatch that cover let me know, otherwise I'll see if I can figure it out on my own. Thanks a heap for the info.

 

No I never had to tackle that connector, maybe someone else knows the trick.

Ya, "if it ain't broke, don't fix it" probably applies here. lol.

George

 

So, living dangerously, I made a temporary connection of that green wire to pin #11. In the process, I also got that stray white tang back inside the cover where it belongs. Removing the cover is just a matter of pressing in a tiny white locking catch at the bottom of the slot located at each end of the cover. I used a pocket-sized screwdriver and did each side one at a time, moving the cover up slightly each time until both were unhooked.

After plugging that connector back into the ECM and starting the car, I observed all hell breaking loose. The tachometer wasn't working, and the CEL was lit. So I quickly shut it off, pulled that green wire back out of the pin and wrapped it up out of the way. My Blue Driver scanner showed multiple error codes set - all involving the transmission. After clearing the codes and restarting, thankfully everything went back to normal.