Heated Rear Window Voltage....

If everything else is working ok I'd strongly suspect a dodgy connection somewhere. It won't be a problem with the window heater itself.

No it should till show a voltage , the heated screen element is a resisting material so its possible the voltage will drop (ohms law )

Can you test the current flowing through the circuit or test the resistance of the window element or wether its got continuity

If you test in the millivolt range you may find a small voltage

It's not the heater, it'll be either a corroded connector or the cable that feeds it will have broken where it flexes.

The only car I have to compare to is my daughters Matiz. It has 12V running through it's HRW and a resistance of 2.1 Ohms.

Mine has about 6v (after flexing the wires to see if better contact can be made) note further flexing does not incresase or decrease the voltage - it appears fixed at 6v now. Again, it only appears at 6v when one of the spades is not connected, once connected and in circuit with the HRW it drops to zero - even when set on my lowest setting.

My resistance for the HRW is only 0.8 Ohms

Thanks to all for offering help.

Kev.

If it's 6v without the spade connected then the wire's broken.

So am I looking for 12v ?

I will attempt to cut back on the wire - passed the flexible area (which has clearly gone bad) and put a new piece in, hoping that I will achieve a 12v volt reading, before connecting back up.

Yes

By definition it will crack somewhere as inconvenient as possible, crimp the ne bit on & push the crimp back above the roof lining so there's a little slack.

I pulled down the rubber covers that allow wires to transfer protected between the hatch and the car body. There are other wires in there related to the rear wiper. I found the thicker black wires for the HRW on both sides and pushed the prongs from my multimeter in until they made contact and I could not find more than 6v - so having bypassed the flexible bit - the problem is clearly somewhere else in the wires path.....

Is there a prime site where I should be looking? The relay looks good and clicks and appears to function, could it be the source of the lost 6v - or do you favour a waisted/cut/rusted part of the wire run somewhere.

Is there a way of determining if the left side or right side wire is more likely to be suspect.

Thank you so much for your help.

One side should be grounded so that'll be at 0V, the other side should have 12V. If the wires are intact then check the actual switch on the dashboard.

Given it's a 306 then I doubt the switch has gone, I'm fairly certain there's a relay just above the fuses , if I'm right then it's the orange one.

Yes Duncan, it is the Orange one. I think I will wait until my son comes home (in his 306) so I can swop the relays and do a proper comparison.

I cannot see a way of testing the relay when it's connected and the terminals don't show any shorts. So I'm happy to wait a few days.

Thank you for your help.

BigNose wrote on 02/01/2010 :

With the spades off the HRW and also switched off - connect your meter set on the ohms range between a good ground and each spade in turn. One spade should have a low value of resistance to ground, which should be below one Ohm. That one is the ground connection - mark it as such. If one reads a low resistance, but substantially more than one Ohm, then you have a high resistance ground connection and have found the problem.

Turn the switch on and the other spade should measure a little over 12v when measured against a good ground connection, even if a low wattage lamp is connected between it and the ground. The lamp should also light. If it does not, or the voltage falls, there is a problem of an high resistance connection on the 12v feed somewhere.

This could be a corroded copper wire, a connection which has burned, a relay fuse or switch etc.. With someone watching the meter reading and another going around the car checking sequentially all of the above points, the voltage will most likely vary as the faulty item is wiggled about.

it is easy enough to discover which of the relay connections goes to the back window, then you can try putting a powered jump lead in that connection and check for 12v at the rear window, if you still have only 6v then you know the fault is in the wire between relay and the back end.