Author Topic: Electrical Gremlins? Voltage drop from 'Off' 'Acc' and 'On  (Read 728 times)

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Offline SR20ME

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It's been a while since I last posted and for those that are wondering, yes I am still tinkering away at my project car, every so slowly.

I have been faced with a frustrating issue at the moment in the way of electrical challenges. About two years ago I installed factory power windows using a relay and the power amplifier and all regulators and connections. Worked perfectly and didn't have any issues.

About two months ago found the power windows did not work at all. Checked fuses, connections and links and couldn't work out why. I later realised that the 12V power connection I used at the back of the interior fuse box did not have a fuse (I mistakenly put this in "fog lamps" which I don't have any).

That is fixed then I discover that when turning the car from OFF to ACC to ON i get voltage drop. To eliminate the problem I took the power window circuit completely out. Still get the same issue. Starts around 12V and above, then goes to 9V and then between 5-6V. I know I am getting resistance or bad earthing from somewhere but don't know how I can trouble shoot this. Alternator was checked and all connections are good as is the battery so it rules those two out.

Even though the battery is reading at the terminals 12+V, could this be an issue once placed under load. I load test it regularly to recharge it.

For those that have diagnosed more complex electrical problems, how would you go about it? I have installed alarms and audio systems, central lock, power windows so I'm okay with automotive electrical.

If it is not the battery one option I am thinking is to rewire the main components with an aftermarket harness. This would be a real bitch. I could do it but it would delay me by one or two months minimum.

Offline SR20ME

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Re: Electrical Gremlins? Voltage drop from 'Off' 'Acc' and 'On
« Reply #1 on: Jan 25, 2016, 05:59PM »
I got another battery today and it ended up to be a bad battery thank goodness! Interesting that a battery can read 12V but cannot hold any load! Thought this was an issue when I would have voltage drop from OFF, to Accessories and then to the On switch.

So if your battery reads 12V with a multimeter, it doesn't mean it can deliver it necessarily.

Offline FNQ TRX

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Re: Electrical Gremlins? Voltage drop from 'Off' 'Acc' and 'On
« Reply #2 on: Jan 26, 2016, 09:44AM »
Glad you got it sorted!

Most battery replacement shops have a battery tester that tests the battery capacity under load.  The tester is designed to show exactly the issue you had whereby even though the voltage may appear good, the available amperage and voltage can drop off and under load.

All I generally understand about car electrics is that if I let the smoke out, then I have to take it somewhere to get the smoke put back in.....
Old guy who should know better than to mess around with old cars.

Offline SR20ME

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Re: Electrical Gremlins? Voltage drop from 'Off' 'Acc' and 'On
« Reply #3 on: Jan 26, 2016, 11:27PM »
Always good to have a multimeter and understand basic elecrical circuit theory.

I have a battery load tester and although the battery was okay when I purchased it (including load), when I load tested the result was that  I could charge it and it wouldn't be any problem.

If you buy a second hand battery from a wreckers, you need to buy a load tester. Went to Prick N Payless yesterday and out of the 5 batteries on the shelf, all but one was good. One only had a 6V reading  from the multimeter (marked for sale as OK) and later that day someone bought it (load tested came as bad). At $45, you want to make sure it's good!

Anyway, good its sorted and not the case of a replacement electrical loom and months of work!

Offline pedro666

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Re: Electrical Gremlins? Voltage drop from 'Off' 'Acc' and 'On
« Reply #4 on: Feb 3, 2016, 01:17AM »
hows your cable from alt to bat?
the words "race car" spelled backward still spell "race car"? 




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Offline SR20ME

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Re: Electrical Gremlins? Voltage drop from 'Off' 'Acc' and 'On
« Reply #5 on: Feb 7, 2016, 07:20PM »
hows your cable from alt to bat?

I'll have a look Pedro. There is one main power cable that runs to the starter. I think it is 4 gauge wire. I haven't done "THE BIG 3" and the previous owner hasn't done this either. It is on my list of things to do.