Rear demister not working???? Celica GT

a bit of logic I =

if the 21W light bulb glows when connected between a good ground & the =

heater ground then the heater gnds faulty, if it glows when connected =

between battery +v & the heater +V thenthe heater feeder wires broken, i= n =

both cases probably next to the point where it goes out the car or into = =

the tailgate.

Indeed. As before, please do not make any further use of the meter. You do not know how to interpret what it reads!

have to move

No, make and use a test lamp as I have suggested!

(I'm wasting my time here, what's the point, if one gives advice and it's not followed?)

I doubt I'll be back on this thread!

'bye.

heat the elements??

just about on the point of giving up!!!

advice. Your assertion that I was using one of the inadequate little test lamps was correct, probably 5w, maybe even less!!

light bulb. Set it up and tested that it worked from a good ground (the original hrw tailgate ground) and the bulbs positive supply from the bulb holder. It lit up brightly. I tested the 12v hrw supply electrode with said bulb. It didn't light, although with the little bulb it did, so you were correct it?s not RECEIVING sufficient current. I also checked between each of it's terminals and a close THICKER part of the element for continuity. The resistance was 0.9 ohms on both hrw terminals, so good continuity.

terminal and utilised the good ground that gave a positive on the bulb test and proceeded to measure voltage across the element, not sure if that was a good idea!!

4.5v reading. Toward the neg side of the element across the horizontal filaments and toward the thicker perpendicular element part there was a progressive diminution of voltage terminating in about 0.5v very near the ground terminus.

parallel on the rear element it didn't illuminate.

the terminal is producing inadequate current and I should consider a bypass from a reliable supply??

You COULD DO THIS, but now you are on the right track, why not pursue it to the supply that it should have and correct the fault?

If you DO use a reliable source, make sure it is fused and that you have a warning light.

I still maintain that this circuit is likely to be alternator controlled and although you have checked the alternator earth, somewhere this circuit is failing. Are you sure that the fuse is supplying the HRW or could it be supplying the relay circuit and the HRW gets a different fused supply via the relay contacts?

A wiring schematic would be useful if you can find one although they can take some understanding!!

to have an electrician as his dad to find that defective tailgate earthing!!!

[...]

You haven't give year or exact model, but for a '99 Celica GT4, Autodata shows the fuse for the HRW is 30A. It's F17, under the bonnet. The HRW relay is number 3, in the same location.

Sadly, no wiring diagram is available.

Chris

Another thought:-

IF this HRW is controlled by a relay, then it may be that the relay contacts are burnt. If you can find another relay of the same type, then 'borrow' it to prove go/nogo (they usually plug in). If the relay contacts are burnt, it may be possible to remove the cover and clean the contacts! (I'd use an eyeglass to confirm burnt contacts, but then I like to know/confirm that a fault is actually cleared, not just gone away to return later!)

As per other reply today, let us know model/year, there's *sure* to be a schematic diagram somewhere ont' net.

The OP's diagnosis using a lamp actually suggests the fault is a broken earth wire in the tailgate.

I wouldn't count on it.

Chris

Hi Chris,

The make and model is a 1997 Toyota Celica GT 2l i st202, not the turbo. I = searched around for a manual, which would hopefully have wiring schematics,= but could only find an american version which wouldn't have identical elec= trical and mechanical architecture to the uk version. I'll have another loo= k online.

Thanks anyway

Hi Chris,=20

The make and model is a 1997 Toyota Celica GT 2l i st202, not the turbo. I = searched around for a manual, which would hopefully have wiring schematics,= but could only find an american version which wouldn't have identical elec= trical and mechanical architecture to the uk version. I'll have another loo= k on interweb.=20

I've tested the hrw earth connection exhaustively, with the Mmeter, the lam= p and it actually grounds another circuit which is working.

Thanks anyway

autodata show two fuses for heated rear window, one is 30a, one is 10, fuse

17 and six plus a relay (no.3) all are in the fascia number 1 fuse/relay panel. the relay is shown with a dotted line around it, which might mean it is optional dependent on country, I don't know for sure.

Hi Mr C

I used this data which states as you said two fuses and the 30a relay

'27 MIR-HTR 10A Outside rear view mirror defogger, multiport fuel injection system'

'30 HTR 10A Air conditioning system, rear window defogger'

'40 DEF 30A Rear window and outside rear view mirror defoggers' I discounted the first one as the fuel injection is working and dont think I have heated rear view mirrors (not certain though), can't find a 30amp fuse noted on the diagram on the inside of fuse panel.

thanks Mr c

The illustration that autodata has shows fuses at the top and relays at the bottom.

The fuses are in 4 lines going vertically and then there are 4 horizontally on the right.

The fuses for the rear window are: 10amp no.6 which is the fourth row counting from the left and the second one down

30Amp fuse no.17 is the third one down of the horizontal fuses on the right.

The relay is the very lowest one (furthest away from the fuses)

=20

Hi Duncan,

I conducted the tests you suggested. the test between heater ground a good = ground didn't light the bulb. The test between bat +v and heater +v did lig= ht the bulb (with the heater grounded to a good earth). So you think the he= ater elements have gone? I think I may have found the fault. I inspected t= he gromet conduit from the car to the tailgate. The heater +v supply wire w= as frayed, exposing the bare copper, just downstream from the multiplug, ju= st before the insulation sheathing wraps around all the wires. This multipl= ug is a real pig to undo for some reason and i didn't want to force it. Is = it likely that the +v supply wire is 'leaking' current as it's exposed?

Do you think the best thing to do is just route a new wire from the car sid= e multiplug connection straight to the heater, or do you contend that the h= eaters defective?? many Thanks

ly a bit of logic I

That cable'll be broken, probably internally or the multiplug terminals = =

have failed, routing a wire past it should cure it, don't use scotchloks= =

for that much current though.

Daydd,

Ok, I'm ditching the Mmeter!! As you've said, it's propitious to back trace= the fault from the fused supply side. A wiring diagram would be very usefu= l.

Maybe the hrw is fed by the relay as you say, it's 30amp so to run the hrw = elements would probably require the extra current to heat them?

I have swapped out both fuse and relay for known good ones, I've visually c= hecked out the contacts in the holder too, cheers.They are feeding other ci= rcuits that are functioning.

I think I may have found the fautl!!! I inspected the grommet conduit from = the car to the tailgate carrying the rear device loom. The heater +v supply= wire was frayed, exposing the bare copper, just downstream from the multip= lug (into tailgate), before the insulation sheathing wraps around all the w= ires. Obvious 15years of opening and closing!! This multiplug is a real pig= to undo for some reason and I didn't want to force it. Is it likely that t= he +v supply wire is 'leaking' current as it's exposed?

Do you think the best thing to do is just route a new wire from the car sid= e multiplug connection straight to the heater.

Also as i mentioned to Duncan, I had a positive result with the bulb from b= at +V to heater terminal +V while it was earthed

Once again, Many Thanks

=20

Thanks Duncan first class!!. So you think I can just do a good splice with = wiring of the same rating??

to the tailgate. > The heater +v supply wire was frayed, exposing the bare copper....

You should have listened to me on the 17th ! ;-))))

Andy C

car to the tailgate.

Yeah I noticed that Andy!!! I checked one grommet but not the other, bit more difficult to remove. Oh well I've done a smidgen of fault finding and hopefully learnt something!!!

Cheers Bud

30A "fuse" on a Japanese car is more likely to be what they call a circuit breaker. 1cm square box about 2cm tall with 2 spade terminals in the base and a clear lid over the fuse link.

The 10A circuit is for the dash switch, warning lamp and relay coil.

Dotted line round relay probably just means its a plug in unit with numbered terminals.

Hi Peter,

Yes I guess it does act as a circuit breaker. It's exactly as you described= . Thanks for having a think for me, I appreciate it.

It's sorted!!!! The frayed end could well have been shorting on the the ta= ilgate metal. It's hard to know as where it enters the conduit when the mul= tiplug rests it's difficult to know its' exact orientation. It's probable t= hough.=20

Unfortunately, one of the plastic tabs on the grommet securing plastic brac= ket broke. I had to do a semi botch job, but it's seems pretty secure. I co= uld use the bracket from the other side, as there's no wiring going through= it, but I would have to be able to detach the multiplug and it seems a wei= rd very secure design and I didn't want to stress the wiring.

Should be ok though. Demister is working like a dream!!!!=20

Thanks again all contributors,especially Dafydd, Andy and Duncan, I appreci= ate the advice wholeheartedly.

Matt