Vehicle wiring pulling my hair out

[ajlelectronics]

Start with all voltage measurements using the battery negative terminal, as that eliminates the earth circuit from the measurements.

Bearing in mind that there may be a small PD from signal earth to chassis.

 

[RWD3M]

No really that was a compliment - @RWD3M...

"Oldgit" @Ubique - is really/trully "not an idiot" and he has broad shoulders - he is not a fool.

I will not end up sparring on here for the above comment.

Oh no, I agree, I wasn't suggesting otherwise.

 

[premmington]

Oh no, I agree, I wasn't suggesting otherwise.

@Ubique got broad shoulders. He is a very nice chap! He is no idiot!

It "just water off a ducks back" for him....


I not keen on people who are "too sensitive" - I like people who will play and have a bit of banter!

I also like people who will debate things - without shutting you down.

I like to see "both" - two sides of a bebate - because "how am I gonna decide who it right or wrong" - unless I get to hear both sides of the arguement...?

 

[Myles1970]

Sorry to butt-in , but I got to the bottom of it. Thanks lads for all your help

 

[Ubique]

Well go on then...
What was the cause? you can't just say 'yep, fixed!'

 

[Myles1970]

Well go on then...
What was the cause? you can't just say 'yep, fixed

I studied the wiring diagram some more, and it turned out that the switched source I was using, was the earth side of another (until then, one I couldn't find) relay

 

[Keithmac]

Just bear in mind you cannot do a resistance test on a powered up circuit, the Multimeter uses it's own voltage across the probes to determine the resistance.

For wiring integrity checks passing a current across the wire is the best bet, a H7 bulb 55w passes 5 amps at 12v iirc.

As people have said above, best bet is to measure potential difference across a loaded circuit (normally to Battery +ve post) when fault finding..

 

[ajlelectronics]

For wiring integrity checks passing a current across the wire is the best bet, a H7 bulb 55w passes 5 amps at 12v iirc.

Seconded. By far the best voltage test is with an incandescent bulb as a load. I use an indicator bulb with a wired croc clip for earth and a longer one with a probe fitted.

 

[Ubique]

I've been 'converted' to Load Pro - does the same, easier to use and can test sensor supply circuits too.

https://www.amazon.co.uk/ELECTRONIC-SPECIALTIES-180-LOADpro-Dynamic/dp/B004IKPUL2

Not cheap, an H7 is more cost effective for occasional use but for me, using it 2-3 times a week, it's worth it.

 

[Keithmac]

I've been 'converted' to Load Pro - does the same, easier to use and can test sensor supply circuits too.

https://www.amazon.co.uk/ELECTRONIC-SPECIALTIES-180-LOADpro-Dynamic/dp/B004IKPUL2

Not cheap, an H7 is more cost effective for occasional use but for me, using it 2-3 times a week, it's worth it.

I might have to try one of those, I seem to end up legged into wiring loom repairs far too often recently..

Looks a handy bit of kit.

Bought the Snap-on Power Probe a while back but haven't got to grips with that yet (haven't really had time).

 

[premmington]

I might have to try one of those, I seem to end up legged into wiring loom repairs far too often recently..

Looks a handy bit of kit.

Bought the Snap-on Power Probe a while back but haven't got to grips with that yet (haven't really had time).

I not into power probes at all - I own a PowerProbe4 - I only really use them for powering things up off the vehicles.

Load pro better idea. This is where I got mine "JB Tools"

Electronic Specialties 180 Loadpro Dynamic Test Leads 60" Long

Buy Electronic Specialties 180 Loadpro Dynamic Test Leads 60" Long with an everyday low price and fast shipping! JB Tools

gb.jbtools.com

In the sale now at £41.99

 

[Ubique]

Same - never bothered with power probe, I've seen the wrong voltage in the wrong place causing the 'expensive smoke' to escape too many times from incorrect use of them.
Load Pro seems to align better to current best practice in electrical diagnosis, and as it's introducing load, not voltage, it's testing the ability of the wiring to support a consumer, not artificially powering the consumer.

I just wish it had standard 4mm termination so I could use backprobing pins & harness breakout connectors properly.

 

[Keithmac]

Yes you are right with the Power Probe 4.

I don't want to use it unless I'm certain I won't damage anything, so that takes time that I haven't got at the moment.

Thanks for the Load Pro link.

 

[m_c]

Same - never bothered with power probe, I've seen the wrong voltage in the wrong place causing the 'expensive smoke' to escape too many times from incorrect use of them.

I cringe whenever I see somebody with a power probe, as it's usually a good indicator that the person using it hasn't got a clue what they're doing.

 

[Keithmac]

I cringe whenever I see somebody with a power probe, as it's usually a good indicator that the person using it hasn't got a clue what they're doing.

Every tool has a job, I have a lot of loom repair and testing kit and at the time it looked like a good addition.

 

[qwakers]

i use a power probe all the time, its a good and fast way of checking component function. it requires the component to be battery voltage ofc. if you're a idiot enough to try to shove 12v down a 5v reference, you deserve what you will get.

 

[Ubique]

I cringe whenever I see somebody with a power probe, as it's usually a good indicator that the person using it hasn't got a clue what they're doing.

There's a tech at M-B Loughborough famously known throughout the dealer group as 'Harry Potter' in recognition of the flashes, sparks & smoke he regularly creates with a wand power probe...

 

[premmington]

I cringe whenever I see somebody with a power probe, as it's usually a good indicator that the person using it hasn't got a clue what they're doing.

I am a "auto electrician" by trade...

You wanna see the mess induced by random use of "power probes" - I see on a weekly basis....

 

[premmington]

There's a tech at M-B Loughborough famously known throughout the dealer group as 'Harry Potter' in recognition of the flashes, sparks & smoke he regularly creates with a wand power probe...

"wand" - that made me giggle/laugh...