Weird Electrical Fault

Susteng

Hi all,

I have this weird problem that when I open the door of my car the dash (DIM as known in the Volvo world) loses power and will come back to life once the door is closed.

I then spent the last two days driving with no working dash as I had the interior light switch in the OFF position and this was killing power to the dash (strange I know) so I isolated the fault to the interior lights as these lights come on when the door opens too. When I put the interior light switch back to the original position the dash came back to life.

But it's not entirely the interior lights fault as it is has to be a bad grounding in the circuit or the extra draw is decreasing the required voltage to power the dash. How does one fault find? I have not yet been proactive in my investigations primarily because I don't know where to begin.

Could it be as simple as bad battery or bad grounding?

I'll explain when the problem first presented itself (after she was at the garage and the mechanic claims no fault). There had been a poor wiring job done on my left headlamp so I sourced a new wiring loom and the garage simply spliced the wires and connected the new wiring loom. Head lamp worked straight away (he claims) but then the problem presented itself. I'm guessing maybe the battery might not have been grounded properly when reconnecting up.

Oh, and the dash doesn't light up when the ignition is turned. The car must be started and then the dash works but the trip counter will always reset to the value it was prior to the problem starting (wish I could say the same about the odometer ha!)

So any suggestions people?

Volvo V50 2006

jca

Was everything OK before the new section of loom was spliced in?

Susteng

Hi jca, yes everything electrically worked perfect.

I also forgot to mention that the radio / cd player will power on with ignition turn, only dash that doesn't work until engine is on.

jca

I'd investigate the standard of work done around that headlamp. Are the joints properly soldered etc? You haven't changed a tail light bulb recently? I saw a case of a faulty stop and tail bulb causing the dash display to dim each time the brakes we're presed. The brake light circuit was feeding into the light circuit, the dash thought the headlights were being turned on and dimmed the display to the night time intensity.

Susteng

I'll have a proper look later. No I haven't changed a tail light bulb recently but the bulb is gone in the main lamp of the headlight with the wiring job done on. I haven't changed this yet and am hoping that bulb is actually gone. Either way, the bulb worked when the dash problem presented itself.

The previous wiring was dodge looking so god knows what way the circuits were going. Strange how the interior lights break the circuit??

Susteng

The soldering looks to be OK but it is possible that the wires may be been soldered incorrectly, as in I know the colours match, but there was one wire before that seem to be apart from the rest of the loom... in the botch job.

ironclaw

Sounds like a bad ground to me. Are any of the new splices making contact with the body? Seeing as it seems to be caused by the door closing and hence a switch action, that would be my guess.

Susteng

Hi ironclaw. Not that I can see, all splices are covered in insulation tape but there's obviously something going on down there.

It is caused by the door opening, or interior lights switched on. Also when turning off the car the instruments will stay in position as the dash powers off really quickly. Could we be looking at an ignition barrel wiring problem?

ironclaw

If the splice was incorrect or there is a live attached to a ground (Or vice versa), bad diode / relay etc, it could cause these issues. Its impossible really to know without tracing the wiring and knowing the exact loom.

Susteng

That's the thing. It's more of a nuisance than an inconvenience.

Last thing I want to do is take it to a Volvo specialist...

jca

ironclaw wrote: »

If the splice was incorrect or there is a live attached to a ground (Or vice versa), bad diode / relay etc, it could cause these issues. Its impossible really to know without tracing the wiring and knowing the exact loom.

Have you ever done automotive wiring? If there was a live attached to an earth ( or ground as you call it) a fuse would blow instantly. I've never seen a diode outside of an alternator.

ironclaw

jca wrote: »

Have you ever done automotive wiring? If there was a live attached to an earth ( or ground as you call it) a fuse would blow instantly. I've never seen a diode outside of an alternator.

BSc. Eng & M.Eng actually.

And I've seen both done by amateurs before, a resistance path meaning you may not necessarily get a fuse blown, it will just drain via another circuit.

Diodes can be handy in a switch system if you want a rocker switch (or similar) to be live on one or both poles when thrown or if you need a cheap and cheerful / nasty voltage drop etc or in some LED circuits. Again, a plenty in third party installations.