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Stray voltage at dome light 1.7V

Stray volts

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#1 Braderunner2

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Posted 16 April 2022 - 04:14 PM

Hi there, I removed the fuse for my internal lights, then checked for voltage at the dome light. There was 1.7volts.

I reviewed the circuit diagram for the UC and it looks like the headlight switch could be the only source of the volts… any ideas what to do next will be greatly appreciated.

Cheers

Paul



#2 Rockoz

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Posted 16 April 2022 - 07:08 PM

There should be power at the light all the time.

It uses earth switching to make it work.

You dont have enough voltage there.

Could be a dirty terminal on the switch or at the fuse box.

Are you using the right setting on your multimeter?

 

Cheers

 

Rob



#3 TOERUNNER

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Posted 16 April 2022 - 08:12 PM

There should be power at the light all the time.

It uses earth switching to make it work.

You dont have enough voltage there.

Could be a dirty terminal on the switch or at the fuse box.

Are you using the right setting on your multimeter?

 

Cheers

 

Rob

If the fuse is removed, i didn't think there would be any voltage to the light



#4 UCgazman

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Posted 16 April 2022 - 10:35 PM

Rob is right, there should be 12v at the light (unless the fuse is removed as the OP stated).

@Braderunner2 - have you tried turning the light sw knob / dimmer switch? I think thats the only place any stray voltage could come from...



#5 Rockoz

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Posted 17 April 2022 - 10:14 AM

If the fuse is removed, i didn't think there would be any voltage to the light

 

Yeah. Just read it again.

 

What is the actual problem you noticed that led to you checking for voltage?

That might help with a better diagnosis.

 

Cheers

 

Rob



#6 Braderunner2

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Posted 17 April 2022 - 10:31 AM

I am replacing the headliner, when I took the dome light out there was a zap which blew the fuse. With a new fuse in place I get 12.8v at the dome light, when I remove the fuse I get 1.8v.

When I drove home last night I had no dash lights, twisted the dimmer a few times, turned headlights on/off a few times… still no dash lights… Today I’ll take the light switch to bits to see what damage I’ve done.

I appreciate the comments Rob and Gazman.

Paul



#7 Rockoz

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Posted 17 April 2022 - 11:11 AM

There is a separate fuse for the dashlights.

Check for that first.

 

Cheers

 

Rob



#8 Braderunner2

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Posted 17 April 2022 - 02:11 PM

Thanks mate…Checked all fuses when I got home last night, unfortunately none blown. Time to do some investigating with my  multimeter! Thanks for the suggestions Rob.

Paul



#9 Bruiser

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Posted 17 April 2022 - 03:14 PM

Do the uc's have a two click pull out parker/headlight switch, with twisting dashlight dimmer function?
If yes, and there is a seperate fuse/12v feed for the dashlights and another for the dome light,
Your 1.7 volts might be tracking across somehow inside the switch.
Should have zilcho voltage if the fuse is out.
I use a can of electric contact cleaner/lubricant and a toothbrush to clean stuff like this

If the round coil the contact wipes on is broken, there go the dashlights.
Can check it with ohm meter too, if you can identify it's lug terminals.

Cheers,
Bruce the roof possum

#10 Rockoz

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Posted 18 April 2022 - 09:19 AM

Do the uc's have a two click pull out parker/headlight switch, with twisting dashlight dimmer function?
If yes, and there is a seperate fuse/12v feed for the dashlights and another for the dome light,
Your 1.7 volts might be tracking across somehow inside the switch.
Should have zilcho voltage if the fuse is out.
I use a can of electric contact cleaner/lubricant and a toothbrush to clean stuff like this

If the round coil the contact wipes on is broken, there go the dashlights.
Can check it with ohm meter too, if you can identify it's lug terminals.

Cheers,
Bruce the roof possum

 

 

Death before domestic.

 

Cheers

 

Rob



#11 Braderunner2

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Posted 18 April 2022 - 02:18 PM

Yes the uc's have a two click pull out parker/headlight switch, with twisting dashlight dimmer function
I opened up the switch and gave it a good clean and applied some dielectric grease to the slidey bits. The coil shows good ohm variations as I turn the switch. All Switching is working fine and had no visible overheated areas.

 seperate fuse/12v feed for the dashlights and another for the dome light,

Im at site now so have to wait to do more faultfinding this weekend. 

Cheers

Paul



#12 Braderunner2

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Posted 14 May 2022 - 03:27 PM

All sorted, installed a new light switch, all instrument lights working… also found my instrument cluster pins needed resoldering… not sure what was causing the stray voltage but it’s gone… for now



#13 Bruiser

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Posted 14 May 2022 - 03:41 PM

Never to return.
Good stuff




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