headlamp washer voltage

[ollya]

Located the pump for the headlamp washers on my 03 CLK W209 as it's not working.
With the ignition off I measure 10.5volts (ish) across the wires leading the pump. This doesn't change with ignition on.
If I press and hold the squirt button it momentarilty jumps by a Volt(ish) I think it does the same when the button is released.

Then it stopped doing anything and made some clicky relay noises inthe engine bay.

Two things...have I fried something?
Can I just connect a car battery to the two pump terminals (disconnecting the car's supply first) and that should tell me if it still works?

Thanks Oliver

P.S. It's a bit strange having a permanently live feed like that I thought?

 

[Ted]

Never use a voltmeter to test if a circuit is live, as the internal impedence is so high that you can pick up a voltage off the very slightest leak.

Best to use a test light to test circuits, and a voltmeter to check charging voltages.

 

[ollya]

Okey doke - will test feed with a lightbulb.
If I just whack 12V on the washer pump should it spring into life?

 

[wemorgan]

It's not just the voltage that needs to be correct but the current too.
ie. I imagine if you connect a 12V car battery to the washer pump you'll do some damage to it.

Hopefully someone more knowledgeable will be along soon.

 

[Ted]

Pretty sure it should.
Don't leave the wires on when you do it though.

Edit: Wemorgan, current is usually limited by the device itself. In this case the washer motor.
It shouldn't do it any harm, but my method would still be to test for 12v across the device.

 

[Number_Cruncher]

I fully agree with Ted's advice - it's incredibly easy to completely milead yourself with a high impedance meter.

Either;

a) leave everything connected, and backprobe the washer motor connections with the voltmeter.

or,

b) disconnect the wires at the motor, and use a test lamp which draws a reasonable current to simulate the load that the motor would place on the circuit.

I prefer to use method a), because you can then check for voltage drop between the battery positive and the component, or between the component and earth with little extra work.

The other virtue of the method is that no changes have been made to the circuit, and you are less likely to have disturbed a bad connection effecting a short lived temporary repair - you're more likely to correctly diagnose where such a bad connection is, and fix it properly.

 

[SilverSaloon]

i had to check my 107 washer pump the other day. completely removed from the car and from the washer bottle, I just connected it directly up to 12v battery via careful connection of jumpleads. i conencted it for a second or so to just test it worked, which it did.

you dont want to run it "dry" (ie no water) for very long.

 

[ollya]

Right I've had it off...connected up to battery...probably wrong way round as didn't see terminals were marked until later...doubt it makes much difference though (except to water direction).
The thing sort of clicks and jerks a little but that's it.
Got one very slight spin out of it on one occasion.
Squirted WD40 in the holes (that were full of mud) now and leaving it.
If it's still not working I'll try and pull it apart.

Anyone know how they are fitted together please?