upgrade to '7427 from '7060 - ready to pull the trigger

[Daveo91]

EDIT 5/3/21: revised attached spreadsheet to latest version with all edits discussed in this thread.
EDIT 11/7/21: revised attached spreadsheet to latest version - updates made to connections at terminals F12,F13,F15 on '7427 PCM


Well I'm finally ready to do this upgrade and have all the plans and materials (I think). I was held up for a long time by the 4L80e in my '91 Burb since I thought it used the Bosch style force motor with required cleaning cycle. Found the good news this week that it's actually the next gen Holley force motor in there so it seems like I should be OK to move forward with the swap. (It's actually a '93 Goodwrench replacement tranny) I have PCM, red/blue connectors, and BIN that should be a good starter for a vortec 383. Time to start the re-pinning project. I used the '91 and '94 G30 with 4L80e pinout diagrams in the two attached zip files to create the attached Excel pin mapping chart. If you go into the Excel it may be confusing at first glance. The 7427 pin addresses are in the middle columns and then you work outward from there to description, origin, wire color, and finally the 7060 addresses in the outer columns. I've double and triple checked what I can and am 99% sure I have everything correct on the 7427 side since there are multiple sources to use for validation. The 7060 pinout is harder to verify with fewer sources available. My plan is to verify wire color as I go along and if there's any disagreement I will have to trace it out and make sure origin is what I think it is.

Not asking anyone to do a detailed check, but if there is something glaring that I'm doing wrong ,or something missing, please point it out. And who knows, maybe this will help someone if there's anyone out there that needs to upgrade from a '91-'93 '7060 PCM.

Many thanks to Dave W for the help, pinout files, BIN, selling me the PCM and connectors, etc.

[1project2many]

You've got a nice chart with great notes for reference. I like it.

When doing an ecm swap I used to find muself checking and rechecking "from" and "to" columns. This was made more difficult depending on how much information was on the reference sheet. Here's a format I currently use as the instruction sheet for the actual swap. I start with the first pin of the old connector and move through each pin to the last. I deal with each wire as fully as possible when I get to it. I will make notes such as "remove from harness" or "repurpose for ..." The marks --> indicate that a terminal should be physically moved. I build it in Excel using three columns and large boxes so there is plenty of white space. I color alternating rows or use alternating fonts to help keep track of the line I'm on. I find this simple format to help me keep track of what's been done and I cross off each step as its completed.

7060 Notes 7427
A1 --> F6
A2 --> E8
A3 --> E9
A4 --> E11
A5 Not Used XX
A6 Remove from Harness XX
A7 --> E6
A8 Not Used XX
A9 Not Used XX
A10 Not Used XX
A11 --> E1
A12 --> E13
B1 Not Used XX

I became confused trying to follow your chart through the VSS pin changes. It appears that you are listing A10 as one of the 7060 TOSS pin locations while the posted image for the 91 FSM shows A10 as unpopulated. You also list B5 as the TOSS signal although the '91 service manual page you've included shows this to be for 4wd vehicles with B11 being used with 2wd. And pin B6, which appears in the manual to be TOSS ground, does not appear in your chart. Not saying you're wrong, just noting inconsistency.

[Daveo91]

You've got a nice chart with great notes for reference. I like it.

When doing the a swap I used to find muself checking and rechecking "from" and "to" columns. This was made more difficult depending on how much information was on the reference sheet. Here's a format I currently use as the instruction sheet for the actual swap. I start with the first pin of the old connector and move through each pin to the last. I deal with each wire as fully as possible when I get to it. I will make notes such as "remove from harness" or "repurpose for ..." The marks --> indicate that a terminal should be physically moved. I build it in Excel using three columns and large boxes so there is plenty of white space. I color alternating rows or use alternating fonts to help keep track of the line I'm on. I find this simple format to help me keep track of what's been done and I cross off each step as its completed.


I became confused trying to follow your chart through the VSS pin changes. It appears that you are listing A10 as one of the 7060 TOSS pin locations while the posted image for the 91 FSM shows A10 as unpopulated. You also list B5 as the TOSS signal although the '91 service manual page you've included shows this to be for 4wd vehicles with B11 being used with 2wd. And pin B6, which appears in the manual to be TOSS ground, does not appear in your chart. Not saying you're wrong, just noting inconsistency.

Awesome, thanks. Feel free to take the excel template if it's useful. And I like your idea of making the simpler chart in Excel for installation instructions. I think I'll do that and also have the more detailed chart on hand for reference.

Regarding the inconsistencies. Thanks for taking a look at these. On A10 for the 7060: I see what you're referencing on the FSM, but on sheet 4 of the 91 G30 wiring diagram it shows A10 connected to a terminal on the DRAC with a brown wire. Or am I not reading that diagram correctly?

On B5 and B6 for the 7060: you make some good points - I need to do some more research this weekend. I think I'll just have to study existing state on my truck before I tear into it. I do have 4wd - in fact the VSS connections are the most confusing part of this whole conversion. My truck has two sensors on the trans, plus one in the t-case. But I think the 4wd trucks that used 7427 just had one sensor in the trans? Will I just not end up using the sensor at the output end of the trans?

[1project2many]

Yes, the diagram shows A10 being used while the more generic pcm pinout shows it unpopulated. In some cases when this happens both pins are connected internally so it probably won't hurt to use an ohmmeter to check the connections. And yes, definitely confirm every wire location on the vehicle as you are making changes.

As the model years went by the TOSS was removed and a calculated TOSS value was created using VSS and gear ratios. For those calibrations it was imperative to know if the transfer case was in low range in order to scale TOSS correctly. You should use a calibration that matches the vehicle wiring. I am thinking that it would be best to stay with the '94 wiring.

[Daveo91]

Yes, the diagram shows A10 being used while the more generic pcm pinout shows it unpopulated. In some cases when this happens both pins are connected internally so it probably won't hurt to use an ohmmeter to check the connections. And yes, definitely confirm every wire location on the vehicle as you are making changes.

As the model years went by the TOSS was removed and a calculated TOSS value was created using VSS and gear ratios. For those calibrations it was imperative to know if the transfer case was in low range in order to scale TOSS correctly. You should use a calibration that matches the vehicle wiring. I am thinking that it would be best to stay with the '94 wiring.

OK, I've done a bunch more digging today - answered some questions but also created additional.

1. I think you're right on the 7060 A10 pin. Looking at the existing connector for the 7060: A10 is unpopulated but there is a brown wire at B11. So I think this should be mapped to F12 on the 7427. But is this correct since I have a 4wd and the service manual says it's for 2wd?

2. 7060, Pin B5. There is a light blue wire on existing B5 connector that I'm fairly certain goes to the rear sensor on the trans, along with the dark green/yellow wire at B6. (I will need to check with multimeter for continuity on esp. light blue wire - the color is faded and I'm not 100% sure it is the same wire that is on B5. If so does it seem correct that I have this mapped to F13 on the 7427?

3. 7060, Pin B6. There is a dark green/yellow wire at B6 that again I'm pretty sure goes to the rear sensor on the trans. So I agree this needs to be mapped to something on the 7427, but where. I have looked at all the available connections for the 7427 and it's not obvious where it should go? FSM lists B4 for 7427 as "Sensor Ground MAP, EGR, Transmission" Would it go here? (sorry if this is a dumb question)

4. A more general question. How does the 7427 know if the t-case is in 4-low? On the 7060, I presume it knows 4-low if it sees a difference between the output trans sensor and the t-case sensor. But on the later PCM, there was no rear trans sensor so I presume the 4-low input became a binary value, on or off? Where does that signal come from? Will I have to mimic it with my installation?

5. My t-case sensor has a purple/white wire and a green/black wire. I see that the purple/white goes directly to the DRAC, but is that where the green/black wire goes as well?

[Daveo91]

Well I have the answer to at least question 4 now. This thread helped a lot, especially 3rd page. Pin F8 on '7427 is the 4-low signal - if it get's grounded out, then PCM knows it's in 4wd. The reason I missed this when I was doing my mapping is I was looking at FSM and wiring diagrams for a G30, i.e. no 4wd options.

So it seems like I just need to figure out a way to ground out F8 when t-case is in 4-low. Might have to get creative as I don't think my t-case or lever has any electrical trigger for when it's in 4-low. No additional lights come on and PCM knows by looking at differential between rear trans sensor and t-case sensor. maybe I can devise a momentary on switch that goes to ground when the lever is moved to 4-low? Go to junkyard and look for the switch on a '94 or '95 with a t-case lever? I'm not sure I'll have any luck finding a ready-made solution since I'm sure my case of upgrading a squarebody to a 7427 is pretty rare.

Still need to figure out answers to the other questions. I'm pretty sure I'm OK on #1 and #2, number 3 is the one I'm most concerned about. Not sure where to map 7060's B6 on the 7427.