HVAC control module / ABS / Brake Light problems

[SnowDrift]

My ABS light came on the other day and I didn't think a whole lot of it, since it came on a couple years ago when I had a bad front bearing. It may have been the next day and the red brake light came on also, but was more intermittent. Again, I didn't think much of it, but thought the two might be related. It might be worth mentioning that my cruise also didn't work anymore while the orange ABS light was on. This morning, I noticed that my HVAC control module didn't work, either. No recirc. light, no fan, no A/C, no door controls, etc. Coincidence on this 1995, 24 year old truck, maybe. This afternoon, however, after about 5 minutes into my drive home, the ABS light went out, the brake light that came on today again, went out, and I tried the fan and it worked. I could select through the blend door positions, at will also. Cruise also worked again.

Can someone give me some advice on this because I have no idea where to start? The voltage on the dash gauge doesn't show at 14v, but hasn't for a long time, in the event this is related. The photo attached shows where it sits on the gauge.

 

[Will L.]

You have a bad connection in one major connection point.
Battery power, main fuseable link, starter battery connection, battery negative, negative cable to engine/ body, bad ignition switch, etc.

 

[MrMarty51]

Gauge on my truck hung like that too.
I thoroughly bright and shiny cleaned all the battery terminals and scrubbed the starter terminals and that end of the cable, removed starter and installed new bearings and brushes, put it all back together and now it shows over 14 volts even with blower and lights on.

 

[THEFERMANATOR]

I would be checking the wires under the fuse panel. That sounds like a loss of battery feed from one of the maxi-fuses

 

[SnowDrift]

Do you mean under the fuse panel that is on the driver side fender?

I cleaned the battery terminals last night and didn't really see much in the way of corrosion - nothing alarming in my opinion. I still had controls and no lights this morning. There's not enough difference here to make me feel that I've found the issue, but regardless, here is a before and after. Before, on the left, is the same as above. Conditions are the same after 20 minute drive, at idle, blower motor on low - defroster might have been on for the before picture, but I can't recall.

 

[MrMarty51]

Have You checked the alternator output with a volt meter ?
I dont remember how these gauges attaches to the printed circuit board, the square body GM trucks had clips that connected the printed circuit board to the volt meter, the clips would loose contact over time, dash would be removed, clips bent slightly, reinserted back into the board, gauge reattached and all would be fine for quite a few more years.

 

[SnowDrift]

I have not checked this. do I just check the voltage on the battery terminals with it running or is it not that simple?

 

[SnowDrift]

Anyone?

 

[Stoney]

The voltage on the battery terminals you can check with it running. But he was referring to the clips in your dashboard behind your gauge cluster. You can test your alternator output yourself or have your local auto parts store do it they do it for free. I'm kind of waiting to see responses on your thread because I've been having a lot of problems with the electrical in my truck to relating to the turn signal switch controls doing crazy stuff. Although mine has not turned a brake light on my heater controls work when they want to, my windshield wipers sometimes refuse to turn off when I put them on high, and my turn signals sometimes go into hyper mode when I turn them on flashing real fast like when you have a bad bulb in the back except it stops after a while and goes back to normal.. just mentioning some of this stuff to see if possibly you've experienced some of the same issues

 

[SnowDrift]

I plan to check the alternator output and voltage at the battery, as well. The next step, I think, is to remove the passenger side inner fender to see if there is anything going on with the cab connection, on the firewall. I did find a harness that seemed pretty tight on the driver side, on the bell housing, where there was a sheet metal flange it was pinched between. I use the term pinch loosely, as I don't believe it was causing any harm at the moment and I didn't see any indication anything had worn through.

 

[SnowDrift]

Well, I figured I should report back on this. After searching for an obvious ground issue, I found no joy. I tried grounds, batteries, etc. It sat for the winter and when I fired it up in the spring, I had the same issue - it had been intermittent in the past. It stayed like this for several days as I drove it now and then. I ended up throwing in the towel and took it to a friend of mine that works at a local dealership. He found this issue very quickly, pinning down the ignition switch as the culprit. I told him I'm glad I took it to him because I would never have suspected that part, since I had just changed it a few years earlier (probably under 10,000 miles ago).

One thing I noticed before it was fixed was that when I would switch my fan from low to off, the ABS light would flicker every time. The switch was apparently losing the ability to power from somewhere. I have the old switch, but haven't looked at it very close to see if I can find an obvious issue.

At any rate, I have all the conveniences I once had and it's getting driven again.