Heated rear screen

If you check the heater its self are you getting continuity?

You would need to unplug it first to test it.

Lee

Sorry Lee I don't understand (retired old fart aged 67}

All I know is that the screen does not warm up. Occasionally, I hear a vague click from the fuse box when I flick the switch to the on position

Julian

>

Pah a youngster my Dad is a retried old fart of 96... Mind you his days of fixing cars stopped about 30 years ago.

The heating elements of the screen are normally connected to the wiring via 1/4" lucar conectors. Lee is suggesting that you disconnect both ends and check for a continunity across the elements.

Personally I'd set the switchery and have the engine running then check there is a nominal 12v across the elements. If there isn't start working you way back to the switch or most likely a relay. to find how far the volts actually progress.

Thoroughly recommend checking that there are volts at the HRW element before delving deeper. I went on a mad chase to find the cause of my non-working RR HRW. It turned out to be a break in the earth cable just short of the screen tab, after I'd had the fusebox out!

There's certainly a relay in the RR so I would expect one in the Defender. The HRW draws 10+ amps which is a lot for a switch.

This

Item NC50Yhas proved surprisingly useful when tracing electrical gremlins incars. I should have used it before taking the fusebox out ;-) Theydid have a version with an inbuilt ammeter which seems to be no longerlisted.

You could, of course, make one yourself from a blade fuse and some lengths of wire.

Richard.

There is a relay, annoyingly it's hidden behind the dashboard and a sod to get to. You need to remove the instrument panel and it should be mounted on the bulkhead, next to a big pink Lucas thing.

Easiest thing to check first is that the heater itself is still OK - disconnect the wire that feeds the screen heater (the bottom one) and put a resistence tester between the two connectors on the heater - you should see a few ohms (can't remember how many, probably less than 10) but what you don't want to be seeing is an open circuit (very high resistence) - that would suggest the heater's knackered. Also check continuity between the upper heater connector and a good ground on the chassis - should be very low resistence.

Guess what I was doing yesterday!

AC.

It was the relay in the end !!

In message , Julian Pollard writes

Which end?

Hi,

I've been reading this thread with interest as my own 90 300tdi(much the same age as Julian's) has not had a working rear screen heater for a few months now.

I don't get 12v at the heater terminal with the switch operated and the ignition on. I do get 12v on one side of the switch and then through the switch when operated. I can't find any blown fuses, the warning lamp doesn't light. But I can't find the relay behind the instrument panel(or any pink Lucas thing).

Should the HRW work with the ignition switched on but without the engine running?

TIA

Neil

(Reply via group please)

My immediate reaction would be 'surely not' but the manual for a 1997 Defender suggests that it does.

"HEATED REAR WINDOW (HRW)

DESCRIPTION The heated rear window (HRW) is operated by a latching switch mounted on the dash panel. When the switch is set to the "On" position, the instrument panel warning lamp will illuminate to indicate the HRW is operating. The HRW only operates when the ignition switch is turned to position "II".

OPERATION Feed from the positive battery terminal is connected to the engine compartment fuse box (C632-1) by a brown wire. Current passes through fusible link 2 and fusible link 4 of the engine compartment fuse box, which are connected in parallel. Fusible link 2 (C907-2) is connected to the ignition switch (C028-1) by a brown wire.

With the ignition switch in position "II" (C094-1), current flows to the HRW switch (C381-2) on a white wire. The switch controls the HRW relay coil.

When the switch is depressed, current flows from the switch (C381-4) to the relay coil (C044-85) on a white/green wire. Current flows across the coil and is earthed (C044-86) by a black wire via the earth header joint(C287-2).

With the relay coil energised, battery feed via fusible link 4 (C906-1) is able to flow across the HRW relay main terminals (C044-87 & C044-30). The energised relay now supplies a feed to fuse 8 of the passenger compartment fuse box (C580-15) on a brown/white wire.

Fuse 8 of the passenger compartment fuse box (C580-16) supplies current to the HRW element (C382-1) on a brown/white wire, and the HRW warning lamp (C929-1), also on a white/brown wire. The warning lamp and heater element are connected in parallel."

The fact that the indicator light does not illuminate suggests that it is a supply problem (good indicator bulb and a functional earth for it assumed) as the HRW element and indicator have separate earths.

I'd be looking at the passenger compartment fuse box to see if there is a supply there. You could also check the downstream continuity and function from there.

Good Lord, why make life difficult when with a little thought you could make it totally impossible? Now which fuse should we check?

Fuse 8 in the passenger compartment. I suspect that if either of the fuseable links in the engine compartment had failed there would be an awful lot of other stuff that wasn't working, from the entire car appearing more or less dead to no lights on one side or all the axillary kit like windscreen wipers/washers/radios/heaters etc nor working.

Wow, thanks for that very useful info. Since last post, I've found the white/black wire feed to the HRW disconnected(loose connector) behind the off-side rear light interior cover panel. Re-connected it but still not working, should be able to check further now though - thanks again.

Neil

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