Door Lock switch and Power Mirror switch getting 8 volts

[sterlin]

As the title says, I am reading 8 volts on these two switches power wires on the main switch board. The power window switch is receiving source voltage and works as expected. When attempting to use the door locks or mirror, nothing happens. No movement and no sound from either. I am new to diagnosing electrical issues on vehicles, this would indicate resistance in the power side of the circuit right? I inspected the wires in the boot going into the cab of the vehicle from the door and found no damage. Where should I look next?

 

[Roadrunner777]

What were the terminals/wire colors where you measured? Also, what were the voltages while you tried to use the mirror/locks? I'm asking that because modern voltmeters do odd things when there is a bad/corroded connection in the circuit. It the voltage stays around 8 Volts, that's one thing. If it drops to zero, that's another. I need to dig out my wiring diagrams and think about this, but if you could reply with the terminal IDs and voltages in use, it would be very helpful.

 

[LG57]

I found that the switches themselves can develop minor corrosion on the internal contacts. The switches can be disassembled and cleaning of the contacts with fine sandpaper(600 grit) will restore an inop switch. Done it several times with window and door lock switches.

 

[J_C]

^ I usually use brasso metal polish on a cotton swab, unless it's REALLY bad.

You can use a voltmeter to measure at any two points in the circuit, while it's powered, to see what the voltage drop across any two points is, for example the switch, or two ends of a wire, etc. To clarify this is both +/- meter probe leads on the positive power wire, or both on the ground, not one probing positive and the other always on a chassis ground point.

 

[Roadrunner777]

What I was getting at with the voltmeter is this... actually, I will give you a personal example: I had a bad brake light. I took the bulb out and measured 12V in the socket. So, I replaced the bulb anyway, still didn't work. So then, I pierced the insulation and measured the voltage with the bulb in the circuit.... zero volts. It turned out to be a corroded splice that allowed 12V of potential voltage until a load was applied, then it failed. Thus, the use of a modern voltmeter can be deceiving. If I had used one of those screwdriver probes with the bulb in the handle, it would have told me the real story immediately.

 

[J_C]

^ Yes, you have to apply power to the load (bulb in your example) to see the voltage drop across the undesired resistive fault in the circuit.

 

[sterlin]

What were the terminals/wire colors where you measured? Also, what were the voltages while you tried to use the mirror/locks? I'm asking that because modern voltmeters do odd things when there is a bad/corroded connection in the circuit. It the voltage stays around 8 Volts, that's one thing. If it drops to zero, that's another. I need to dig out my wiring diagrams and think about this, but if you could reply with the terminal IDs and voltages in use, it would be very helpful.

I apologize for the incredibly late response, I'm finally living back where the explorer is located. I read about 8 volts on wire 171 BK/W going into the driver door lock switch, and wire 171 BK/W going into the power mirror switch, both on the main driver switch panel thing. Where should I be voltage dropping in this system? Should I voltage drop from one of the connectors under the dash to the switch? If so, which connector would that be? I have the electrical and vacuum troubleshooting manual.

 

[sterlin]

Well, those were the numbers I got a few weeks ago when I tested it then. Just now, I tested the door lock switch again, and it read about 2.6 volts, and went to 0 when I pressed the switch in either direction.

 

[J_C]

Take out the fuse in the under-hood power distribution box. "Might" be fuse #6. It should be hot at all times, so using a multimeter, determine which contact for the fuse is 12V relative to chassis ground. Also, make sure it is 12V, or same voltage as the battery voltage if battery is drained some.

Once you know which contact is live to battery, use the OTHER contact, and measure resistance between it and wire 171 at the driver's door switch panel. If resistance is very low (single digit ohms), move on as it isn't the problem, unless disturbing the wires temporarily improved the connection.

If the resistance is too high, yes you may have a bad connector and I can't tell you where they are, would just follow the wire trying to trace it. On the other hand, possibly you have a short to ground. With the driver's door switch panel disconnected, measure resistance between wire 171 and chassis ground. Should be infinite (out of range) ohms, no continuity. If it is, then plug the connector back into the switch and measure again. Resistance should still be infinite, if not then it's likely the switch has a fault. This is only when you aren't pressing any switch buttons. Pressing the button completes the circuit to ground and resistance will be whatever that particular motor's resistance is plus a slight bit for the wiring.

Instead of resistance you can also measure for voltage along the circuit. Pick any two points, like the power distribution box fuse contact, and the switch panel, and put your two multimeter probes on these two points. If the voltage difference isn't very low (less than 1V, certainly not a ~4+ drop for it it be 8V in a 12V system, let alone the 2.6V you just reported, then the fault is between these two points.

Keep in mind that the most likely situation is you didn't find the/a frayed wire in the door hinge boot, unless this is a flood vehicle and all the electrical system is corroded, or someone has already altered it for whatever reason and made bad connection or left wires loose to vibrate (against the sharp metal edge of a bracket or something) and damage the insulation to cause a short.

 

[sterlin]

Take out the fuse in the under-hood power distribution box. "Might" be fuse #6. It should be hot at all times, so using a multimeter, determine which contact for the fuse is 12V relative to chassis ground. Also, make sure it is 12V, or same voltage as the battery voltage if battery is drained some.

Once you know which contact is live to battery, use the OTHER contact, and measure resistance between it and wire 171 at the driver's door switch panel. If resistance is very low (single digit ohms), move on as it isn't the problem, unless disturbing the wires temporarily improved the connection.

If the resistance is too high, yes you may have a bad connector and I can't tell you where they are, would just follow the wire trying to trace it. On the other hand, possibly you have a short to ground. With the driver's door switch panel disconnected, measure resistance between wire 171 and chassis ground. Should be infinite (out of range) ohms, no continuity. If it is, then plug the connector back into the switch and measure again. Resistance should still be infinite, if not then it's likely the switch has a fault. This is only when you aren't pressing any switch buttons. Pressing the button completes the circuit to ground and resistance will be whatever that particular motor's resistance is plus a slight bit for the wiring.

Instead of resistance you can also measure for voltage along the circuit. Pick any two points, like the power distribution box fuse contact, and the switch panel, and put your two multimeter probes on these two points. If the voltage difference isn't very low (less than 1V, certainly not a ~4+ drop for it it be 8V in a 12V system, let alone the 2.6V you just reported, then the fault is between these two points.

Keep in mind that the most likely situation is you didn't find the/a frayed wire in the door hinge boot, unless this is a flood vehicle and all the electrical system is corroded, or someone has already altered it for whatever reason and made bad connection or left wires loose to vibrate (against the sharp metal edge of a bracket or something) and damage the insulation to cause a short.

View attachment 425403

I was able to read the same 2.6 volts at a connector up in the dash (I believe it was C213), all of the wiring that I am able to inspect looks perfectly fine there. Is it possible there is a damaged wire in the engine compartment coming from the fuse box to the connector on the firewall (C147)? I have yet to look there yet.

 

[BKennedy]

If it's the switch, aftermarket door switches are inexpensive. I replaced mine with an entire set I got on eBay.

 

[sterlin]

If it's the switch, aftermarket door switches are inexpensive. I replaced mine with an entire set I got on eBay.

I did take apart the switch and clean the contacts (they were very dirty), but it still isn't going to work with 2.6 volts, I'm going to peek around in the engine bay tomorrow.

 

[J_C]

I was able to read the same 2.6 volts at a connector up in the dash (I believe it was C213), all of the wiring that I am able to inspect looks perfectly fine there. Is it possible there is a damaged wire in the engine compartment coming from the fuse box to the connector on the firewall (C147)? I have yet to look there yet.

Yes, the fault could be anywhere between (or in) the power distribution box and the switch. If you are reading 12V on the downstream side of the fuse, you could even run a new wire from that point, as far as reasonably possible which is probably the door jamb connector. You could do a test run, routing the wire outside the vehicle before stringing the wire through. I have test leads I made, with alligator clips on both ends, that makes it easier to form this kind of temporary connection for test purposes.

Then again, these aren't exactly "high value" vehicles so altering the factory setup wouldn't be a big deal, you could even drill a couple holes in the fender wall and the door, put rubber grommets in them, and run the wire the whole way to the switch... putting a loop in it, in the door hinge area, so it has more of a length to flex when the door is open/shut. Best would be high strand count (solid copper, especially not copper clad aluminum), silicone insulated wire, from a trusted source... generic chinese silicone tends to fall apart in single-digit # of years when exposed to the elements. You don't need to think about that as much if you don't need to replace the wire segment in the hinge area so it isn't subject to being repetitively flexed.

 

[Rdc#1958]

I found that the switches themselves can develop minor corrosion on the internal contacts. The switches can be disassembled and cleaning of the contacts with fine sandpaper(600 grit) will restore an inop switch. Done it several times with window and door lock switches.

Well I disassembled my mirror switch awhile back and sprayed inside with electrical cleaner also the spring steel contacts tend to not make good contact but bending them slightly will restore them I had that problem with my Mountaineer.

 

[sterlin]

I just had an idea. I currently share a battery between my 1997 F-150 and my 1992 Explorer. Whenever I put the battery in the explorer, I think I might be smashing the harness from the maxifuse box. I will send pictures tomorrow, I think this may be where I find the damaged wire, and it would make sense now that the voltage is lower because I keep swapping the batteries out and smashing the harness further.

 

[J_C]

I'd definitely need pics to understand this, since there's just the single wire from the battery to it and it shouldn't be routed on the battery tray where putting a battery in mashes it. I would think about getting a second battery.

 

[sterlin]

I'd definitely need pics to understand this, since there's just the single wire from the battery to it and it shouldn't be routed on the battery tray where putting a battery in mashes it. I would think about getting a second battery.

This harness that runs near the battery tray here that runs all the way to C147 into the cab near the brake booster. I notice that it pokes out into the battery tray, so sometimes when I put the battery down it crushes the harness a little.

 

[J_C]

lol, I thought I was going to see pics of what you have yourself, not a diagram, but I suspect there is some wiring misrouting issue, as no wires should be subject to this. Has this vehicle had the wiring altered? I suppose it is a matter of how much work to do, to put things right, but none of the wiring should be subject to this kind of issue even if you never swapped batteries in.

 

[sterlin]

I had to pull off some corrugated tubing and electrical tape but I did find what I thought I would, looks like a previous owner put a simple crimp in here before and it rotted away and broke as I was taking it apart. The crimp is the blue rectangle that turned blue from corrosion. I will be fixing this tomorrow most likely.