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Electrical Issues: Advice Needed!

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Old Mar 5th, 2017, 13:28   #1
Ambz642
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Default Electrical Issues: Advice Needed!

So we took the dashboard out of my 480 as the heater rear window light was constantly on and so is the light around the ignition barrel.
We took out the Electrical Control Module, gave that a looking over and that looked fine.
We discounnected the wiring loom connected to the heated window and light went out so must have something to do with the wiring loom?
Where do we start?

Thanks
Amber.
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Old Mar 5th, 2017, 22:20   #2
dcw
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Welcome to the joyous world of 480 electrics!

You say the heated rear window light was always on - was the actual heated rear window, do you know? If it was simply the indicator light in the instrument panel that would be an odd one - PCB failing getting current to the light somehow?

Could you never get it to go off? Should go off after 12 minutes with a quick press of the switch, or stay on until switched off if you hold the switch long enough to get a "beep". Could you generate a "beep" by holding the switch down?

Since you say you disconnected the wiring and the light went out, that suggests the whole circuit was live and staying on all the time. Could be a faulty switch - the switch packs are known to pack up.

Most likely culprit though is the CEM - I presume that is what you say you looked at, but solder joints crack, the little relays on the PCB give up, etc. Most electrical problems on the non-engine side of things in these cars go back to the CEM, in all honesty.

Ignition switch light is an odd one - it should operate with the other internal lights. Are they working properly in the unit in the roof? If the other interior lights are working OK then something's wrong specifically with the wires to the light bulb by the ignition barrel I think - poor earth or crossed contact. Not sure whether wiring to ignition barrel light runs in same loom as that to the panel light for the rear window - perhaps it is a simple case of two wires chafing in that loom and making contact. Only carefully checking the wiring will reveal that I guess.

If, however, a careful check shows that the interior lights are all not working properly, again I'd check the CEM very carefully.

I was just looking at your earlier thread - you mentioned driver's mat being wet. Water might have worked into the wiring loom up behind the instrument panel/steering column so if there is any chafed insulation that could be what's allowing contact.

Keep us posted and hopefully we can guide you further - but 480 electrics are a nightmare at times!

Good luck

David
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Last edited by dcw; Mar 5th, 2017 at 22:23.
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Old Mar 6th, 2017, 11:23   #3
eye of ra
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I agree with dcw the CEM or Heater Switch are most likely at fault.

Disconnecting the wiring from the CEM eliminates a fault in all the wiring from the CEM to the Light, the heated rear window and the heated mirrors and proved the current lighting the lamp is coming from the CEM meaning the heaters themselves will also be on (assuming they are still connected and working).

The only possible wiring fault would be a short to earth in the wiring from the CEM to the Heater Switch, again the heaters will also be on. This can be checked with a multimeter on pin 20 of the large connector (black/red wire) with the switch in the off position.

Also as dcw has said the ignition switch light will almost certainly be a different problem and unless all the interior lights are on a little confusing and may depend on your model year as this wiring did change a bit over the years.

Last edited by eye of ra; Mar 6th, 2017 at 11:45.
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