I've run into this situation on a few occasions in the past and most recently today. I used to work in the automotive aftermnarket for several years and have been out of it for the last couple. Scenario: Customer brings in vehicle stating drivers front power window does not work. Turn on key and try for myself and sure enough no function. Check fuses and find none blown or missing. Pull switch or door panel to check the circuit inside the door. Turn key on and probe the switch with DVM to see if switch is sending voltage to motor and widow "mysteriously" rolls down. Put vehicle back together and system continues to work normally. Happy customer picks up vehicle with minimal labor charge never to be seen again (no news is good news). I've run into this on all types of circuits but on rare occasion. I've had this happen on windows, locks, horn, cruise control, stereo and lighting both factory and aftermarket. Friday on my way home from work my aftermarket head unit lost power. Today I decide to get off my lazy and check it out. Turn the key on and still no power. Pull the radio out and check (DVM) constant power and I have 12.5V. Probe switched power and turn on the key and the radio powers up. I'm curious if any other 12V guys have run into this and what you think or know causes this.

 

A loose connection that was "fixed" when you moved wires to remove / inspect the parts.

 

A valid possibility but that loose connection most likely would show back up later down the road. I worked in the aftermarket for a little over fifteen years and had customers follow me from shop to shop. I would think eventually those "fixes" would have caught back up to me when the problem reapeared. The window example I gave was with a man who followed me for about thirteen years in a 89 Town Car. The car was three years old when I "troubleshot" the window and I last did work on it in 04. If it was a loose connection I think the problem would have reapeared in that time (maybe not). Some of the other circuits I mentioned had no diassembly or movement of components involved. Take the horn for example. Nothing moved or removed, just probe the connection at the horn, push the button and the horn works.

EDIT:
In the cases where disassembly was involved I do remember that no funtion changes happened until probed with my meter

 

maybe you have a magical DMM.. can i have it? :p

 

How about a rental, can't loose the majic!

 

LOL, My DMM only tells me that something is broken, and makes my lazy *** have to fix it. Its awesome that yours does the fixing for you! I want one like that

I def wouldnt wanna lose that magic either, if I were you... Don't ask questions, just go with it, lol!

 

In all seriousness, to answer the question in the OP... No, I've never probed wires and had it fix the issue... Maybe you're just getting lucky... Im speaking from over 10 yrs daily experience with a meter...

 

joeymc13, I know what you're saying. If it aint broke dont fix it. It's more a curiosity as to whether other installers have run into this and have an explanation. It's been far and few between that this has happened but it has so I'm curious if this has happened to others. When I was in the industriy I strove to learne and understand the nuances of everything I touched. Likewise after getting out I'm accused of being meticulouse and a nit picker. After today I ran into the old "meter fix" on my head unit and I thought I would throw this ? out there since I've always said when asked "what was it?" and I say "I don't know".

 

I know what you mean man, its crazy! Sure, I've taken power off electronics and reintroduced the voltage, and for some reason, doing that has fixed it, but I have no idea how probing a wire with a meter could have an impact on that circuit. I mean, trying to think about it from a scientific point of view... Lets say you're testing for voltage... Well, yeah, you are using your chasis ground on one side of the meter, the other side goes to the circuit in question... Well, we def know we're not introducing a new voltage source to that circuit, the only thing left to think about is, are we creating continuity with the ground side? I don't think we are, bc I think that most meters diode isolate the ground side from the ground of the circuit in question, so honestly, I have no idea nub... I'll tell you though, I wouldn't mind a meter like yours still... I mean, I've never had my meter magically fix any malfunctioning circuit, so, if I used that meter for another ten years, and only had it fix one thing, It'd be worth it to me, LOL!

But, I cannot figure out, physically, how testing for voltage as you stated you were doing with the power window situation, could introduce something new, electronically to the circuit, to cause a "fix"... My best guess was a messed up contact like tunernOOb posted, but like you said, you would think that the problem would resurface down the road, esp since no measures were taken to prevent it from happening again, bc you didn't consider a bad contact to be the problem! I know my time in the industry is relatively youthful compared to some other guys on here, so hopefully, one of those guys will chime in, and teach us both something new! I'm very curious at this point!

 

That's what I'm looking for is experience and years in the industry to try and explain or give theory for this. Your ten years is testiment that my experience is rare but may have been experienced by others. I see your MECP cert. in you sig. so I have to give you cred. for knowledge of 12V circuits. I've thought that maybe a relay was locked up by residual voltage and was tripped loose some how by my probe.

 

I appreciate you noticing my MECP cert, but to be honest with you, all that means in the whole scheme of things is that I can pass a 200 question test, regardless of whether or not I have actual 12v experience, lol. I've seen ppl that have never worked on a vehicle's electrical system in their life, pass the MECP basic exam. I am very confident in my 12v knowledge however, but not due to MECP, but due to the 10 years of experience I have in DC work... Im more proud of my FAA certs in electronics, they don't hand those babies out to just anyone who can memorize a flash card! I did make that part of my sig though to just try and give some credibility to my posts to those who don't know who I am...

 

bump....

Bc im curious if anyone has ever experienced this, or has any ideas how it could happen...

 

It is not an uncommon "issue" in most cases it is a connection issue, contacts get "oxidized" just the act of unplugging and re-plugging a connection is all it takes to "clean" the connection, and in many cases the problem does not return.

We run into that issue once or twice a month, [Dave Ward Auto Electric] with the same results, unplug something to test and plug it back in to fix the problem, we now also spray contact cleaner into connections and add a little dielectric grease. 94

 

This is understandable but what if the circuit was not unplugged? In most cases I've run into this nothing had been unplugged yet. Just like with my radio I pulled it out, turned on the key and moved the harness around thinking possible bad connection, nothing. Checked constant power, good, turn on key, check switched power, radio powers up.

 

You removed a door panel without unplugging the switch????? 94

 

That's not what I said. I said pull switch OR door panel to check circuit (a generallity). Checked for power at the switch and window started working. No need to pull the door panel since function returned after the switch was probed. Although you should know some door panels can be removed without unplugging the switch. Likewise some switch panels can be removed without removing the door panel or unplugging them.

 

Like sarcasm, a "generality" is not that apparent in text.

However, just the act of pulling the switch out of the door panel and moving the leads to it, sounds like enough, [in your case] to have fixed the problem.

After 35 years in the buisness I do know that some switches or door panels can be removed without removing/unplugging the other, i just can't think of a Honda/Acura off the top of my head that that can be done with. 94

 

True enough, point taken.

Moving the leads around and unknowingly "fixing" the problem has been mentioned but I don't buy that. With the window example the switch and leads were moved with no change prior to the meter being used. No change checking power comming to the switch. Check for power comming out of the switch and the window rolls down. I've dealt with intermitant problems before and generally they show back up later if the problem wasn't actually solved. Who knows maybe it's just dumb luck.
This was a Lincoln btw

 

Well that's the problem, it's a Ford. 94