No CEL/MIL or Airbag lights on cluster, 98 A3 AHU

I believe a p.o disabled these 2 warning lights, either to ignore them, or to defraud the next buyer (whom i bought it from).

The bulbs are in the cluster, but they never light up. The airbag light was located in some extraneous slot, like ABS, and I moved it back to the Airbag slot. (i did not verify the bulbs are working. i'll check them when i can.)

There are also some dangling wires behind/above the fuse box:
- Red F wire in a Blue M plug
- Br/Yel M wire in a Black F plug
- Blk/W M wire in a White F plug, comes from D/4
- Blk/Yel M wire in a Grey F plug, comes from D/7

Does anyone recall any experience with these wires? I'm wondering if they could be related to the dead lights. If the M/F connectors matched, i could assume the four were originally plugged into each other, but since the genders are mismatched 3-to-1, two of the males are relegated to "just watching", so to speak.

It's possible the airbag system is shot, as the heater core had previously leaked, and was bypassed. I read on here that sometimes that leak will kill the SRS controller directly beneath it. (Great engineering, btw. Was there no spare room in the front bumper, to mount that computer?)

The only wiring diagram i could find, containing any hint to the airbag light was a 98 V6 that said:
T50/30 ----br/yel---> T1 ----white---> T28b/1. The "Br/Yel" got my hopes up briefly, but i have no idea where T1 is. (it didn't say "T/1"; "T" has 2 pins, and the loose Br/Yel won't fit).

I wish i could answer these myself with a Bentley, but i've read too many posts about how incomplete & inaccurate their wiring diagrams are. i hate to be one of those "There Oughtta be a Law" guys, but every new car should include a full, accurate service manual. That way, Bentley & VW can't point the finger at each other, while leaving us in the dark.

There are a few non-connected wires hanging around the fuse block. Some are for options, some are just to make you guess what they're for.

Thanks, ninedee. Turns out 3 bulbs were toast, but not to the naked eye. The p.o did move the airbag light to hide it, though, i'm sure. CEL was there, but burnt.

Well...... I lost my CEL again. I loaned out this Mk3 several months ago, and within 2 miles the guy burned out my clutch. Apparently in hindsight, it was slipping a little bit, but it never got anywhere near unusable for me. Also in hindsight, I've criticized this guy for his footwork and pulling away in a too-high gear, in other cars. And he burned out a clutch in another 20-year old car, a few months earlier.

Being too pissed off to fix it at the time, I parked it and drove my other Mk3 instead. Then I started working out of town, and didn't have time to fix it, so I put a 12v, 2-watt solar battery maintainer (Coleman brand) in the window, and let her sit in the driveway. That was months ago.

This weekend I opened the door to check on her, and she was going nuts. The temp gauge was flicking back and forth from far left to far right, making a clicking noise. The fuel gauge was pegged about 1/2-inch past Full. Whiskey Tango F**ktrot.

Pulled the solar device out of the cig lighter, and she went quiet. Plugged it back in, and she was possessed again. Checked the solar plug with a voltmeter, and it was a cool, perfectly normal 18.9 volts. Popped the hood, and the battery was about 1.5 volts.

So, I put a real battery charger on it for a few hours, then turned the key, just to see what was what. Temp was down to 0/160 as normal, but Fuel was still over-pegged to the right. Most of the warning lights came on, but not CEL. So I cycled the key several more times, and no CEL. Put my fingers on the 109, and could definitely feel it clicking On, then Off. Then I put the 109 in Mk3 #2, and it produced a CEL there, so it's verified working. Turned on the stereo, fearing the worst. It took a few seconds to load the USB stick, and worked fine.

The battery wasn't charged enough to attempt a start, so I gave up for the night, worried about what all got fried -- ECU, possibly something in the IP? None of the weird electrical behavior made sense, because the instrument cluster SHOULD have been isolated and turned off, due to there being NO KEY in the car to switch the circuits on. Everything should have been electrically isolated, without a key in there. If the 18volts was migrating into the cluster on its own, then I guess it got into the ECU as well.

So this morning I went back out to a fully-charged battery, and decided to try connecting it with VagCom. Scratch that, I have the Torque app and a bluetooth OBD2 scanner, so I tested it on Mk3 #2 first. Key On, CEL On, App On, Synced and Connected. Good.

Walk over to Mk3 #1. Key On, CEL Off, App On... Synced and... Connected? Really? Good. Will it start? Throw the key to Start, and... Nothing. Off, and then Start again. Nothing. Oh yeah, this is the one with the flaky Alarm box or whatever. Couple more turns of the key, and she fired up instantly. Tach works, Fuel still pegged hard right, everything else looks OK, but no CEL.

Then I pulled the cluster to inspect the bulbs. CEL bulb has resistance, doesn't appear burnt, so I swap some other bulbs around, and they're all good, except when I put them in the CEL slot.

Disconnecting the cluster, however, did reset the wonky Fuel reading, and that gauge is behaving normally again. The Blue High-beam light is also not working; no idea if it's related to the CEL. I visually checked every fuse, and they all look good. Tried checking the G1 block under the dash, but those wires don't match the diagram I referenced. The diagram says the CEL wire is Yellow/White, which I found at pin#28 of the red connector on the cluster (which also has continuity to the CEL slot). I wasn't able to see that wire on the rats nest below, though.

As for that damned solar battery maintainer, my only guess as to what happened is, it got cooked in the back window during a heatwave, fried the voltage regulator, and began sending 18v (or even more???) unfiltered into the cig lighter port. Still makes no sense to me how the volts made their way into the cluster -- without a key -- but also somehow stopped charging the battery. If I write a letter to Coleman, do you think they'll recall these stupid things, and relocate the voltage regulator down the wire near to, say, the cig plug, instead of up on the solar collector where it gets hot as hell?

Me neither. Damn, I still have to change that clutch too.

I'd still write to Coleman and express some discontent about their product failure.

Yeah, I don't know what the consequence of pumping 18+v through the cig lighter is going to do. The factory charging panels were much less, I think they might have been sub-5v but I couldn't swear to it. All I know is I have tried to charge a cell phone via the OE VW charging panel and it wasn't able to do much.

I am sorry you lost the clutch, I don't understand how people destroy things so quickly. At any rate you're best off to not allow that kind of thing anymore.

It sounds to me like you're going to get through this without a lot of pain but not sure what the resolution for the cluster issues are at this point. Perhaps you can send it to Chubbs and he can deal with it?

Steve

Went back in and probed the two wires for Highbeams (T28#25) and CEL (T28b#28). Pulling the highbeam switch was giving me 12v at the wire (which had good continuity to the bulb, and the bulb was also good), but produced no light when I plugged the cluster back in.

The CEL wire would momentarily blip up to 3.5v or so, then drop back to zero, when I turned the Key On. I'm not sure exactly how the light is supposed to work. Perhaps the ECU is supposed to light it up, providing 12v for as long as light is required. Or perhaps the ECU sends a pulse to the cluster, and the cluster decides how long it's supposed to be lit up.

Disconnected and reconnected the cluster a couple more times, and now the Highbeam light works again. But still no CEL. It's a small victory, but I'll take it.

Yesterday, I thought the Fuel gauge was working normally, but I didn't remember how much fuel was in the tank. I found my note that, when I took her out of service, I'd used 2.0 gallons (from a full, vented neck), so when the gauge read 5/8 full yesterday, it was definitely wrong. Then today, after getting the Highbeam light back, the Fuel was reading Empty. So I probed around the junction block, and got "0v", "1.3v" and then "4.9v" -- whatever those are supposed to mean. Then I connected the cluster one last time, and got a Full reading on the Fuel gauge.

I dont know, maybe there's a flaky ground somewhere. I recall now, the last few months of driving that car, the fuel gauge was reading low at the top end (wouldn't quite reach Full), and wouldn't become accurate again til it got down to 3/8 or 1/4 or so. Whatever was causing that, may still be lingering.

Since I don't get smogged or state-inspected, and I won't be selling the car ever, I don't need the CEL so badly. I can just OBD-scan it periodically. I might take one last stab at tracing the source wire, and hopefully sticking a probe in it will bring it back.


Steve, my brother had his own weird problems with phone chargers in cig lighter ports. He would get zero charge in an Escalade; slow charge in a F250, good charge from an AC outlet -- but by far the best charge he ever got........ was from the cig outlet in an excavator one day.