in my case, once I replaced my vacuum pump the light went off. Is there any sign of baring ware like grease around the vacuum pump pulley or residue coming out of the diaphragm?

My pump was in spec, drove with the light popping on/off for a bit. Starting learning to ignore it, bad idea! I had just completed the dual belt tensioner. Went on a camping trip, on the way
home started to hear a faint squeak then within 100 miles the vacuum pump baring froze while driving. Shredded my serpentine belt and I lost braking power and power steering. Was white knuckling trying to get it to stop while the family was in the truck. Couldn’t do a roadside repair
because nothing in area had a vacuum pump or the serpentine belt size. Got it towed home in middle of the night. Put a new pump and no light since. After that incident I went crazy and replaced a bunch of parts in the braking system. Plus I bought 3 new serpentine belts!

i have learned one thing about the sequence of replacing 25+ year old parts on my truck is once I put something new and it starts working as new, something else within that system has to work harder and the ware starts to show quickly trying to keep up to the new parts. Just like when I chipped the truck, I thought the tranny was fine until my torque converter started slipping. Put a new fuel pump then had a leak in a fuel bowl sensor. I found that most of the original parts are ticking time bombs at this age on my truck and need replacing just from a maintenance standpoint.

I know what I am sharing may not be much help in diagnosing but an old vacuum pump and “Brake” light on the dash is how it all started for me.

 

Well, since the bitter, hateful cold resided, at least temporarily, I was able to take another look at this one. As part of my monkeying around with things, I was unable to identify any vacuum leaks. Maybe me hearing one was only my imagination. It's hard to say at this point. I also reseated the electrical plug at the module that distributes the vacuum. I noticed driving the truck a few minutes later that the light wasn't on! It came on for a little while after starting the truck after I had briefly parked it at the gas station. I have high hopes that if I clean up that connection really well that it'll be better.

I appreciate everyone's help on this and for everyone's patience with me taking forever to get around to fixing it.

Edit: It's still happening, but it's much more intermittent now. I notice that unplugging that connection makes the light go out. That makes sense, because unplugging that would open the circuit for that bulb. This also confirms that the light being on is a result of something going on with the vacuum.

 

I'm thinking about just hosing that connector down with contact cleaner and getting a little brush in there to clean all of the contacts and hoping that clears everything up. In the case that it doesn't, and just as a what-if, I was looking for replacements and found that there just aren't any. What's the deal? Do people just disconnect the switch and just not worry about it? If so, I'm tempted to do that myself.

Am I the only nerd who cares about this?

 

I finally found some time to care about this last night and hosed out both sides of that electrical connection at the vacuum manifold doodad with a liberal application of electronics cleaner and then reconnected it after the cleaner dried. I drove to work and back today with no warning light. That's a good sign.

 

good to hear. Sometimes it’s the simplest solution but the long path to get there.

 

I'm glad that I resisted the temptation to fire up the parts cannon.

 

Putting on coolant filter right now before it gets dark 😬

 

Well, the warning light was back on when I drove to work this morning. Does anybody have any suggestions?

 

pull the cluster apart and remove the bulb....

 

Or piece of black duct tape to cover

 

I just disconnected the vacuum sensor/switch thing and the problem is good. I’ll probably double-check, again, that I am making sufficient vacuum (tested fine before) for my own peace of mind. This way, the warning light will still work for low fluid level and parking brake (once I get the parking brake switch fixed).

 

HVAC controls working like it should?

There is a line near the passenger hood hinge that breaks and not allowing fresh air valve to work and can suck in moisture to kill the pump with too much air

 

As far as I can tell, yes. According to my Harbor Freight vacuum gauge, she’s making sufficient vacuum. Brakes work fine and vent controls seem to be working fine.

If you or anybody else has any suggestions for things to try, I’ll be happy to give them a shot.

 

I know I mentioned above but I went through this for a bit. My vacuum was good but still had intermittent light. Maybe when under load while driving it’s not performing the correct vacuum.

Does the vacuum pump have signs of wear? Squeaky while running? Grease coming out of diaphragm or behind pulley? Is it the original to your knowledge?

when my vacuum pump went out, I had the light come on/off then baring just froze mid drive and ripped up the serpentine belt.

 

Thank you for your thoughts. I replaced the vacuum pump probably fifteen years ago, but I probably only have 10,000 miles on it.It shows visual signs of age, but not necessarily wear. The pump I installed would have been the cheapest unit that I could quickly find, because things were tight for me, financially speaking, at the time. Among the spare parts that I keep in the toolbox in my truck is a fresh vacuum pump, vacuum pump pulley, and a fresh belt. I also keep a pulley puller and installer kit in there. So, I should be good to go in the event that a roadside repair becomes necessary. I'm hesitant to use the spare, though, just because they do cost money and I would then want to get a new spare to keep in the truck. That, and the vacuum gauge indicated that it is making sufficient vacuum, and the frequency of the intermittent issue seems to change depending on what I am doing with that electrical plug.

When I get some time, I may try installing my spare vacuum pump and then keeping the old one in the toolbox as a spare. Then, I suppose if the light goes away, that would condemn the old pump.