XJS- heated rear window

[stigproducts]

Got an 86 XJS with a non functioning heated rear window. Seem like I am getting 12v to the rear and the relay seems OK, but no de misting is going on.

It is possible the timer function doesnt work as I have noticed the dash light stays on past 10 minutes, although I haven't checked to see if the 12v maintains through 10 mins.

I had a look a long the lines and can't see any obvious breaks.

Anyone any thoughts?

[melhook]

you may have 12 volts at the screen, but do you have an earth on the other side? if so, there are a couple of simple checks.... using a multimeter, very gently run you probe over the screen elements from the inside, ( with other probe on a good earth ). check for 12 volts at various points along the screen. Alternatively, you can measure resistance along each element from left to right,( should be close to zero ohmn's) but be very gentle with it. if this all checks out, then even though you have 12 volts you may have no amps due to a poor connection or corroded wire, you can either connect an ammeter in the circuit, ( from 12 volt wire onto screen ) or using a decent test light, see if the 12 volts will light the bulb brightly. Good luck.

[stigproducts]

Thanks Mel. Test results
-Earth is fine
-A test light connected to wires on both sides lights fine
-With multimeter earthed I was getting 10 volts along most of the lines, although that dropped to 5 or 3 right at the end of the lines for some reason....
-Resistance across each line, wasn't 0 but it was consistent across most of the lines

Been twisted up in the back seat with a magnifying glass looking for breaks, which was a laugh! Repaired a few possibles with that silver electode paint stuff

Still doesn't demist though

[melhook]

well i would say that if the voltage is dropping across the screen it is due to poor connection / high resistance, therefore i would think that the fault is with the rear screen itself. good luck

[glassman]

Of course it's in my interests to try and sell you a bit of glass, but if the problem is pointing towards the elements, a rear window for an XJS Coupe is not as expensive as you might expect.

Even with FC insurance, the price of the glass is not much more than the excess value.

Paul.