IrishJoe

Hey guys! Ok, I got an interesting one for you. I used to be a Mercedes tech and did a ton of evaporators. My Suburban needed a new evaporator, so I thought, no big deal I got this, pulled the dash, pulled the air box and replaced it. Reinstalled everything and fired up the truck. Dome lights went out, battery warning light came on and the fuel gauge was dead. D'oh! Check the dome light fuse its blown, putting in a new one immediately popped the fuse. Crap, know I smashed a wire even tho that's a totally rookie mistake and I know better. Pull the driver's knee panel and sure enough, the heavy brown wire coming from the ignition switch that goes over to the interior fuse panel is smashed between the crash bar and the steering mount and is grounding. Pull that out, repair the wire, check all over for any other stupid maneuvers I might have done, looks good, put it back together. Dome light fuse is fine now, won't pop. Still have the battery light on and fuel gauge inop. Ok fine, figure maybe the battery is low, voltmeter shows the alternator is charging fine so I'll go drive it for 20 minutes and charge everything up. Truck runs fine, battery light never goes out. Temp gauges (both the engine and transmission) don't seem to be working, as they didn't go up at all during the 20 minute drive. So I've torn back into this and cannot for the life of me figure it out. Here's everything I know:

1. Red battery warning is on in the information center, comes on at run position, stays on during start, goes out when the truck is turned off
2. Fuel gauge is inop. Does not move at all with key in any position
3. Temp gauges (both engine and trans) seem inop, but bumping the key from acc to run and back gets them to jump up a little light they are just reading cold so not positive on them
4. Instrument cluster has a good ground at A6, is hot all the time at A9, is hot in off, run and start at A10, is hot in run and start at B6. Is NOT hot in run at A4 (little brown wire) and I believe it should be
5. Traced A4 brown wire to the interior fuse box to CRUISE fuse. No power at CRUISE fuse. Fuse is fine. No power coming in on the other leg
6. Checked every single fuse with a multimeter and visual inspection in the engine fuse box
7. Checked every single fuse with a multimeter and visual inspection in the interior fuse box
8. Interior fuse box has power at some of the fuses, not at others, regardless of key position. CRUISE fuse for example never gets powered up, which if the A4 wire is supposed to be hot in run would indicate it should be (provided I traced that properly which I believe I did)
9. Blower motor is dead, but I believe that's because the truck sees the battery and has killed "unnecessary" electrical draws (clearly it doesn't know how hot it is right now)
10. Alternator is a rebuilt GM part from GM installed about a month ago for a different problem
11. Battery tests good
12. Speedo, tach, voltmeter and oil pressure gauges all work just fine
13. Truck starts and runs just fine, drives around with no issues other than the above problem

I know the battery light comes on when the PCM detects an issue with the battery, so I'm now worried that I shorted out the PCM with the smashed brown wire, but I don't know if that would explain no power to part of the interior fuse box. Instrument cluster already has the issue of not being able to see the mileage, so was considering the cluster might have not enjoyed getting removed, but the no power at A4 has me second guessing that. I did find reference to the problem of "battery light on, fuel gauge and temp gauges inop" in a few other forums (S-10, etc) so seems like this is an issue that has happened to others, but none of them reported back what the fix was.

I think that's everything. At my wits end here and grateful for any suggestions.

Thanks!

kevinkpk

You didn't mention it, but did you disconnect the battery?

IrishJoe

Dang it! I tried so hard to list everything lol. Yes, multiple times disconnecting the battery, including having it disconnected for probably 4 hours while I poked and prodded at the wiring harness. I'm assuming that would be enough to reset the PCM but I didn't do anything special to try to get that to happen.

IrishJoe

Alright gents, I figured it out and decided to post the fix here for anyone who has the same issue. Turns out when I said I checked "all" the fuses I really meant I checked all of the mini fuses and then got lazy and visually checked the maxi fuses cause they're a pain to get out. The IGN 1 Maxi fuse under the hood provides power to the CRUISE fuse in the cabin fuse box, drivers side. The power comes in on the large orange wire that comes down from the ignition switch. However, the large orange wire and the large gray wire that I'd smashed in the crash bar are both powered by the Maxi fuse, so when that popped, it took out power to the CRUISE fuse even tho the orange wire is the one that supplies the CRUISE fuse, not the gray one. So if you have the symptoms above, battery light on and fuel gauge inop but the voltmeter shows the battery is charging, you have most likely lost either the IGN 1 Maxi Fuse or the CRUISE fuse, as they will cause the same symptoms, or you have an open in the orange wire coming down from the ignition switch (or possibly the ignition switch itself if you got power going in but not coming out). I really hope this diagnosis helps someone since I spent a ton of time figuring it out since I was too dumb to check the fuses like I knew I should.