Electrics: 850: Volvo 850 GLE T5 Display failure: Rev Counter / Temperature

[mseville]

Has anyone come across this intermittent problem: when a sat nav and a dashcam are together plugged into the cigar socket, it sometimes causes the engine temperature gauge to read zero, the rev counter to jump about all over the place (including hitting full deflection with considerable force), and the automatic gearbox fault to be displayed (orange upwards arrow).
There was no problem this time on the out-journey towing the caravan, but upon return after a few days standing, and with significant load (air conditioning plus the internal fan) this occurred again. Incidentally, the caravan does have a lot of 12volt (non-LED) running lights*.
[1] Does anyone know of a cure without sacrificing one of the driving aids?
[2] *would switching off the running lights help the situation, and if so, how would I do this? (I have wanted to do this for a while, anyway, so that the caravan brake lights coming on would be more apparent).

[Cookeh]

Originally Posted by mseville

[1] Does anyone know of a cure without sacrificing one of the driving aids?
[2] *would switching off the running lights help the situation, and if so, how would I do this? (I have wanted to do this for a while, anyway, so that the caravan brake lights coming on would be more apparent).

Sounds like you're overloading it to be honest. Could try using the yellow auxiliary 12v feed that is under the dash.

You can switch the running lights off by turning the small screw in the bottom right of the switch panel counter-clockwise.

Try posting in this section of the forum - might get a better response:
https://www.volvoforums.org.uk/forumdisplay.php?f=16

[green van man]

Only time I've had trouble with the rev counter not working or fluctuating was on a Volvo 460 when the alternator was packing in.

Your symptoms seem load related but the load should not cause a problem given the capasity of the alternator if in good working condition. I suspect it's on its way out,possibly new brushes are needed, probably easier to replace it and be done with the job.

Many firms refurbish alternators and sell through motor factors, 12 month garentee. Genuine Volvo will likely be refurbished but a lot more expencive. I paid £120 for a Volvo one for that 460 20 years ago, only because the available much cheaper factor one was minus the rev counter terminal.

Paul.

[dingov70]

First port of call is to check security of all connections , followed by cleaning & re-making any earth connections . It sounds like an earth fault .

Satnav & dashcam are not power hungry devices when compared to other electrical items within the car . Seeing as this fault occurs when the cigar lighter is used to provide power , that would be my starting point .
Remember start with the obvious & work outwards , undo & reconnect any joint , see in any leads move intheir fixture & make sure any leads going to earth are tight

[DaveNP]

If you were to take the caravan off and drive down the road, using the high beam headlights would add 2x55w load to the system, the caravan would have to have 22x5w running light bulbs to add that load, so I wouldn't expect it to be that.

My personal experience of the 12vsocket/cigarette lighter is that the one in the front is pretty well trashed in an older car so you get a poor connection, if I need a 12v socket I use the one in the back of the centre console as presumably the kids in the back didn't smoke, and back when the car was new they didn't have phones, ipads, etc.

[mseville]

To turn off the running lights: I'm not sure which screw to turn! Help, please. Mine is a 1995 Volvo 850 GLE T5 Automatic.