Volvo Owners Club Forum - View Single Post

dcw · Mar 5th, 2017, 21:20

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

Mar 5th, 2017, 21:20	#2
dcw VOC Member Last Online: Apr 18th, 2024 21:35 Join Date: Jan 2007 Location: YORK	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 __________________ VOC 400 Series Register Keeper The current fleet: 1997 440 LE, 1996 460 CD, 1994 480 GT and 2007 V50 SE Sport Last edited by dcw; Mar 5th, 2017 at 21:23.