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Author: Subject: Testing a loom for a short circuit
roadrunner

posted on 8/5/20 at 05:21 PM Reply With Quote
Testing a loom for a short circuit

I've been having fun figuring out how to splice two looms into one.

I believe I have the write connections but still have issues.
So I purchased a new battery as my test one is old and knackered.
Before I fitted the new battery I thought I would use my multimeter and test for shortages.
Straight away I found that I had continuity from the battery connection on my ign switch to ground. Crap.
Anyway, I found that the ignition light bulb/housing could be my problem.
With the bulb fitted I have continuity from ground to positive.
With the bulb out there is no continuity.
I'm guessing this my issue, or am I being thick.

Brad.

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theconrodkid

posted on 8/5/20 at 05:59 PM Reply With Quote
for the ignition light, it earths through the alternator so the bulb holder should not be earthed





who cares who wins
pass the pork pies

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gremlin1234

posted on 8/5/20 at 06:00 PM Reply With Quote
without knowing your exact wiring, I would guess the 'ignition light' is the indicator from the alternator, which should light when ign is on, but engine not running. in this case some continuity would be expected. you need to set the meter to ohms, and see what that reads.

put simply, if you test a light bulb with your meter will indicate continuity

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roadrunner

posted on 8/5/20 at 06:47 PM Reply With Quote
Thanks fellas.
But surely when you switch the ignition on, you shouldn't have continuity to earth.

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gremlin1234

posted on 8/5/20 at 07:22 PM Reply With Quote
quote:
Originally posted by roadrunner
Thanks fellas.
But surely when you switch the ignition on, you shouldn't have continuity to earth.
yes you will but... this is when you need to be checking volts.
In many ways I prefer to use a 5w 12v lamp over a multimeter, but it's a bit 'old skool'

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roadrunner

posted on 8/5/20 at 07:26 PM Reply With Quote
I'll connect the battery tomorrow with the bulb removed and see how it goes. What's the worse that can happen.
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gremlin1234

posted on 8/5/20 at 07:42 PM Reply With Quote
quote:
Originally posted by roadrunner What's the worse that can happen.

I suggest you get yourself a co2 fire extinguisher, (halon would be better but you cant get them) powder is very messy, water is ok, foam again messy

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harmchar

posted on 8/5/20 at 08:43 PM Reply With Quote
Be careful with that ignition lamp. I was doing a rewire of my dash and striped all the wires off the tell tale lights without taking photos or drawings. Got sidetracked with other jobs and went back to dash a year later. Wired up the way I thought it normally should be, i.e. +ve to the centre post of the bulb and -ve ground to the bulb holder. First time I went to start the engine, the loom melted all my earth wires in my loom.
I was Sierra pinto, with a butchered Sierra loom. Blue wire from alternator to the centre post of bulb and a switched live to the -ve post of the bulb holder if I remember correctly.
I found a good diagram, I will try to post if I can find it.

This one, but wire from my alternator was blue and not red as per photo. Hope this lets you see how it's wired
ign tell tale wiring
ign tell tale wiring


[Edited on 8/5/20 by harmchar]

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roadrunner

posted on 9/5/20 at 09:03 AM Reply With Quote
Thanks
Will look at it today.

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roadrunner

posted on 9/5/20 at 07:16 PM Reply With Quote
Just to say that I don't think that there was anything wrong.
I replaced the bulb and holder just incase. But with every wired up correctly all is fine.

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