12.7 questions

Yes, Swan and thank-you. we have a national weather thunderstorm warning for this area and I came into town. I was able to print and scan this schematic. I also made a special folder to save these and hopefully start a little library. I think that this may be a schematic that refers to the engine interface harness and a pretty good general one. I know the SRS and TRS sensors are here. I guess I know their location as I have changed them a couple times now. I ran across something in passing in the last couple of days that showed pin outs of the 30 pin plugs and a way to test the wiring. I made a stab at it, but eventually got the idea that the wires were in the wrong place as this was the case on the rpm guage. I was able to find the wire number of the rpm guage on the schematic that I am guessing Penske had put in the main electrical center middle dash. this was a very good schematic. then my buddy happened to have an extra vehicle interface harness that went as far as I think it is the 31 pin plug on the cab. I picked through that harness and found the rpm wire, I think it is like 505 or something. but it was at the top of the plug instead of the bottom. And what do ya know? mine was in the exact same spot. Now for the SRS and TRS sensors and wires, I am gonna try to refind the article that I had found with the troubleshooting instructions, unless you happen to have it handy. but I am expecting that I am probably going to have to totally disassemble the harness to follow those wires eventually. I think that there is something that I would like to get to the bottom of before that. and that is the power wires for the ECM itself. I am pretty sure this is the top plug on the vehicle interface side. I found all but one of these all wadded up in the loom back near the battery box and the wiring was pretty redneck in my opinion. Well, anyway, that is what I'm up to now. tonight I am going to work on a library. tomorrow, I am thinking it will start to dry out some and I can start redoing this wiring to look something close to what you would see on a schematic. This is what happens to your truck sometimes when you work under the authority of others and they demand that you use their mechanics etc. and you just have to be smart enough to undo the damage.

 

Ah-ha! Here I am. Found a bunch of schematics. And made it back out here to take a look at some wiring. Stopped at my buddy's to look at one of his simular trucks. From what it looks like, harness was too short for the other side and somebody improvised. My battery box is on pass side rather than drive as there is a pump in that location on drive side. I see there is a hot wire and you need 1 hot. Others are grounds. Would have been nice if they had grounded them rather than wedding them up in the loom. From what I remember on the rpm guage, abnormality goes clear to the ecm this was my fear before it went to Detroit. I asked for and was charged for an ecm test. And their diagnosis waa it was the guage. We can all pretty well figure this was wrong by now. I didn't know as much as I do now about ecms but the high- non variable voltage was coming from the ecm. Not saying there ain't problems back that far though. Still testing a little here.

 

Well, I lengthened the original harness. It was still there. Took out the splice they had put in. Didn't put in a special box as I looked and didn't see one on a couple other old flds. Grounded the other 2 wires. My buzzer and dash lights seemed to be much brighter and louder. The ecm was grounding a little somewhere but not where and how it was designed. I think this could be a reason for some failure over a long period. It has been that way for several years. I looked. There is a wire coming into that harness near the ecm, but I have been operating for about 4yrs with an ungrounded ecm. Granted. It has been parked for a lot of that time. I was just looking for info to start testing all of the sensors and wiring I may have located another ecm same year/motor/truck etc. There may be issues in the ecm but want to test all other sensors before I try it.