Interior lights don't come on s70

[BEJinFbk]

How does the harness look at the back of the radio?
Sometimes radio installations get a little sloppy...
It's worth having a look at, even if there's a stock
deck in there now. It's all about the pink wire.

[MrAl]

Hi,

It could be that any connector that was removed was not fully inserted back together again. Thus moving it around might make it make contact again. If it happens again, check to see that any connectors are fully inserted by pushing them together again.

When most connectors are installed in electronic equipment they are crimped onto the wires. Each connector pin is crimped onto each respective wire. Sometimes the crimp is not perfect so any movement could cause the wire inside the crimp to work it's way loose. This causes the wire to loosen more and more as time goes on and eventually starts to oxidize and that starts to interfere with normal current conduction. Once it gets too bad it means something doesnt work. Moving it around could temporarily remove some of the oxidation and therefore even a loose connection might make it for a while again.
If that's the case then the problem will return and so the bad crimp will have to be found.
That's if Volvo does connectors the same way most of the electronics industry does connectors.
From what i have seen so far though Volvo uses pretty solid connectors. Just hope they were all installed correctly.

[BEJinFbk]

These are open barrel, Molex type connections.
A bad crimp is exceedingly unlikely.

[MrAl]

These are open barrel, Molex type connections.
A bad crimp is exceedingly unlikely.

Hi there,

Well, how do you define "exceedingly unlikely" ?
"Exceedingly unlikely" is not the same as "Can't ever happen".

If there are 10 thousand cars made and each has 100 crimps, that's 1 million crimps.
If only one crimp is bad that's 1/1000000 or 0.0001 percent chance that one is bad.
If you are one of the 999,999 you dont have a bad crimp, but if you happen to have the bad one, you have the bad one
The only way to know for sure is to wait and see, then look to see if there is really a bad one or not.
Of course there are other possibilities such as a broken wire that makes contact intermittently.

In my years of experience in the power industry i've seen bad crimps so i know for a fact this can happen. Heat cycling makes it worse, which is always typical in an automobile. The expanding and contracting works the connection loose over time.

[BEJinFbk]

Exceedingly likely means that I'd look for much more likely things first.

Usually, that's the power supply, headlight switch, the dimmer itself or
a hacked up harness that was inflicted on the car by a previous owner.
Usually it's a radio "upgrade" that didn't involve a wiring adapter kit or
someone tagging into dash illumination for something or other.

I'm not sure if your experience is with 12 volt systems or something with
greater AC voltages and current characteristics, but in my experience, a
low current open barrel crimp made by a production quality crimper will
most likely outlast the car.

[MrAl]

Hello again,

Yes that makes sense, but try to keep in mind this was just an added suggestion on what could be wrong, not necessarily what is wrong. I like to cover all the bases

Low current? How much current actually flows in that circuit? I dont have any specific info on this i just figure that there must be several bulbs involved. Anything over about 100ma might be called "not low" depending on the application. In a bad crimp the joint acts as a higher resistance so it may block all or some of the current.

I've worked in theory and practice with systems from 1vdc up to 240vac single and three phase systems. Power electronics covers a wide range of power circuits and devices, from say 1ma up to 1000's of amperes. The ampere range in which i've actually worked though was more like maybe 10 picoamps up to maybe 200 amperes. This includes sine synthesized converters and PC power supplies, amplifiers, regulators, etc.
I own (or owned at one time or another) many books on electronics and electrical theory, and currently own thousands of electronic parts collected over the years including micro controllers ic chips, MOSFET's, etc., because i still do a little bit of this as a hobby and try to keep up on theory to some degree also.

All this talk got me to remember one more small detail. That is, when some connector crimps do go bad they often heat up quite a bit. This can be noticed by feeling the connector metal body, or by noticing a burnt appearance in the connector body plastic. Some of the connections we worked with long ago had big connector bodies so we could feel each one in turn to check for heating as the device under test was run for several hours. That would reveal a bad crimp and so it was fixed before the item was shipped.

Again, im just bringing this up in case this is the problem here or with some other car. It's just one possibility, and one i know could cause the same problem being talked about here. The general topic is probably just "loose connections".