Low voltage at power outlet

[boyse7en]

Hi all,
My 2007 Accord Tourer is giving me a headache.
Bought a mini compressor to blow up my paddleboard. Plugged it in to the power outlet in the boot and nothing worked. Thought it would be the fuse - nope, that seems fine. Checked for voltage at the plug (ie where the loom plugs into the back of the power outlet socket) and I'm getting 4v.
Bit stumped now. What could causing such a drop in voltage?

[GreenV8S]

Sounds like a wiring fault, although I've never seen a fault that would drop the voltage to 4V off load rather than breaking the circuit.

Anything else on the same circuit that could potentially be pulling the voltage down?

[boyse7en]

GreenV8S said:

Sounds like a wiring fault, although I've never seen a fault that would drop the voltage to 4V off load rather than breaking the circuit.

Anything else on the same circuit that could potentially be pulling the voltage down?

I've never known anything like it. I'm no auto electrician, but I can usually get either 12v or 0v and trace it back to find the fault - fuse, dodgy connection etc.
Getting a low voltage is a first for me.

[Oldandslow]

Earth fault? Check voltage between +ve and a good earth point (bolt into body etc). If you get 12v between the +ve and the body then it's a bad earth, if it's still 4v then it's a fault on the supply side.

[Chris32345]

High resistance somewhere in the circuit checking the wiring around the boot for the earth point and clean it up with wire wool


If you still have low voltage and the wiring around the 12v looks ok Chen the fuse box connection looks clean

Also check the negative battery pole and main earth connection



Then you have to start Tracing the wiring through the whole car

[Penelope Stopit]

As above, check the circuit through

Nothing unusual happening, it's a common fault

[boyse7en]

it's not an earth fault, the reading is 4v whether i earth through the -ve wire on the plug or straight to a known good earth on the car body.

[eltax91]

My '08 accord tourer had an issue that was almost the same. It used to work sometimes and not others. Some time after the ETG finally packed in. Once the wiring harness in the hinge was repaired and the ETG started working again, the boot socket worked all the time again.

Check the wiring for the ETG in the hinge, as it operates it chaffs wires, but continues to work until they eventually break. Could be causing a drain when open?

[paintman]

What sort of multimeter are you using?

Reason I ask is I had an issue with the in-tank petrol pump on my RRC.
Pump wouldn't run at all on the vehicle.
Connecting a spare battery to the pump's lead saw the pump run fine.
DIGITAL multimeter connected to the vehicle's loom plug showed battery voltage.
Testing loom live wire at the plug with a bulb produced nothing. Not even a glimmer.
Using a pin to probe the wire along from the connector lit the bulb about an inch back from the connector.
Stripping the wire showed 30 odd years of exposure had corroded the wire to a couple of strands - enough to show OK on a digital m/m but not to power the bulb or the fuel pump.
I wonder if an analogue meter would show reduced voltage?

[GreenV8S]

Is the voltage drop occurring on the positive or negative side of the circuit? That will give you a clue as to the type of fault you're facing.

[E-bmw]

GreenV8S said:

Is the voltage drop occurring on the positive or negative side of the circuit? That will give you a clue as to the type of fault you're facing.

^^^^Wot 'e said.

Simple laws of physics that should be bread & butter for an auto electrician to find for you, it can only be high resistance in the circuit causing reduced voltage V = I x R.

[Penelope Stopit]

E-bmw said:

^^^^Wot 'e said.

Simple laws of physics that should be bread & butter for an auto electrician to find for you, it can only be high resistance in the circuit causing reduced voltage V = I x R.

Nice to see "I" used for current

Why do some use V = A x R ?

It does my head in it does, that's not difficult though

[boyse7en]

paintman said:

What sort of multimeter are you using?

Reason I ask is I had an issue with the in-tank petrol pump on my RRC.
Pump wouldn't run at all on the vehicle.
Connecting a spare battery to the pump's lead saw the pump run fine.
DIGITAL multimeter connected to the vehicle's loom plug showed battery voltage.
Testing loom live wire at the plug with a bulb produced nothing. Not even a glimmer.
Using a pin to probe the wire along from the connector lit the bulb about an inch back from the connector.
Stripping the wire showed 30 odd years of exposure had corroded the wire to a couple of strands - enough to show OK on a digital m/m but not to power the bulb or the fuel pump.
I wonder if an analogue meter would show reduced voltage?

A standard digital multimeter. I also tested the voltage about 3-4cm back from the terminal and it is 4V there as well, so not corrosion/wear at that point.

[Artykay]

I'm intrigued now.
Did you measure the resistance between the negative to the good known earth point?
I've seen totally corroded cores inside insulation that looks fine, Totally broken cores inside a wire that looks fine as well that got me.
Good luck.
Got a circuit diagram?