Mystery current draw

[rar110]

I'm trying to solve some electrical issues on the 110, in particular no brake lights.

I've discovered current passing through two fuses despite nothing being turned on. The two active circuits are through the top two fuses on the left which are:
1. Horn, interior light; and
2. Hazard lights.

Fuse diagram below:



74250



Any suggestions about where I should look and what the problem could be?

Thanks

[BilboBoggles]

How much current?

[steveG]

Can't offer much on the current issue, but is the brake light switch on the back of the pedal box working OK?

Issues I've had in the past with rear lights have usually been poor contacts, bad earths etc.

Be interesting to know if the residual current at those fuses is in the normal direction. I'm no auto elec, but know that bad earths can produce all sorts of weird stuff with current from other circuits finding its way back to earth through other paths.

Steve

[rar110]

How much current?

After frying my last multi meter I'm reluctant to check.

[rar110]

Can't offer much on the current issue, but is the brake light switch on the back of the pedal box working OK? Issues I've had in the past with rear lights have usually been poor contacts, bad earths etc. Be interesting to know if the residual current at those fuses is in the normal direction. I'm no auto elec, but know that bad earths can produce all sorts of weird stuff with current from other circuits finding its way back to earth through other paths. Steve

Brake lights problem turned out to be a bad connection at the bullet connector. I'm going to replace the hella truck style tail lights with LEDs and will replace the bullet connectors with heat shrink connectors.

[manofaus]

How did you check for current draw? Both circuits you mention always have 12v supply. Otherwise you would need to have keys in ignition and accessories on to work.

Pull fuse and check both clips against earth for voltage. You should only have 12v on one side if fuse. If so change meter to ohms or resistance and check again but only the side that shows 0v. Make sure all your doors are closed!!!! If you get some sort of number you may have a problem.

[rar110]

How did you check for current draw? Both circuits you mention always have 12v supply. Otherwise you would need to have keys in ignition and accessories on to work. Pull fuse and check both clips against earth for voltage. You should only have 12v on one side if fuse. If so change meter to ohms or resistance and check again but only the side that shows 0v. Make sure all your doors are closed!!!! If you get some sort of number you may have a problem.

Thanks. My auto electric knowledge is growing from a very low base.

I've interpreted voltage at both ends of the fuse to mean current was passing through on its way to somewhere. However all that meant was the circuit was live. Current was passing through on its way to my test lamp and then multimeter only.

I did as you suggested. Power feeds into the fuse from the left. There was no ohm reading on the right terminal, which I interpret as no open circuit?

Thanks

[BilboBoggles]

The only way to easily measure current is to put a meter in line with the circuit. the simplest is to pull the fuse, put the meter in 10A range and jam the probes into the socket - so in effect your meter becomes the fuse- you'll need to probably move your terminals to the 10A current range. Most meters will survive high currents for a second or two - it probably won't be very high current other wise the fuse would have blown.

It's correct for those two circuits to be permanently on with a voltage present, your interior lights will work without ignition key and so will the hazard lights.

[steveG]

The only way to easily measure current is to put a meter in line with the circuit. the simplest is to pull the fuse, put the meter in 10A range and jam the probes into the socket - so in effect your meter becomes the fuse- you'll need to probably move your terminals to the 10A current range. Most meters will survive high currents for a second or two - it probably won't be very high current other wise the fuse would have blown.

It's correct for those two circuits to be permanently on with a voltage present, your interior lights will work without ignition key and so will the hazard lights.

The gotcha with using your multimeter as a current meter is you need to make sure you put the probe lead back in the voltage socket afterwards, otherwise when you go to check a voltage next you'll dead short through your meter from the supply to earth. When that happens some have protection and you can simply replace a fuse (usually a strange size one that you don't have at home), but cheap ones may just let the smoke out :(

Although I know my way round a multimeter, I've also got a current meter similar to this one these Automotive Current Tester Mini ATM APM Blade Fuse BOX Board Meter Circuit Test | eBay (http://www.ebay.com.au/itm/Automotive-Current-Tester-Mini-ATM-APM-Blade-Fuse-Box-Board-Meter-Circuit-Test-/170936154549?pt=UK_Diagnostic_Tools_Equipment&hash=item27cc96b9b5)

Easy to use and leaves your hands free.

Steve

[manofaus]

My advice is not to use your multimeter to measure current. You will get caught out one day.

Thats why you check resistance first. 10a is not much for a short to ground. If you must measure amperage get a set of tongs.

[rar110]

My advice is not to use your multimeter to measure current. You will get caught out one day. Thats why you check resistance first. 10a is not much for a short to ground. If you must measure amperage get a set of tongs.

I will probably buy a DC clamp meter one day.