fj62 dome light circuit parasitic draw (1 Viewer)

[Devils Paw 80]

I've recently developed a parasitic draw in this circuit, even with both lights switched off. It was enough to drain the batter after a few days, so I've pulled the fuse for it. I suspect the problem has to do with the rear cargo dome light wiring, but not sure. Anything else on this circuit, besides the clock? Also wondering if the clock could be responsible. So, if anyone else has had this issue, feel free to chime in.

 

[WHG423]

I put LED bulbs in my dome light and rear cargo light. When it is dark, I can see that the rear cargo light is always just faintly illuminated indicating that it is drawing a small amount current constantly. Being LED, the power consumption is minimal and not draining my battery. I assume you are experiencing the same condition. I have yet to trace mine down as it is not really a problem, but curious what you find out.

 

[Oaks]

Mmmyyy wondering if this may be happening to me. Subscribed

 

[C130FE]

I subscribed. I may have the same issue. Mine sat for a few days, actually seven, and the battery was dead. Granted it's an older battery.

 

[CardinalFJ60]

Carb cooling fan relay. BTDT.

 

[C130FE]

Carb cooling fan relay. BTDT.

Carb cooling relay? Parasitic? I ill have to check that also. Did you just replace yours? what did you end up doing? Thanks.

 

[CardinalFJ60]

Carb cooling relay? Parasitic? I ill have to check that also. Did you just replace yours? what did you end up doing? Thanks.

Yep parasitic draw..about .1v or more IIRC. try this...test the draw, then pull that fuse, then test it again. I bet it's gone. then...turn the key, with the fuse back in place. test it again, I bet it's back. I found when I powered that relay it would create that draw. you can also disconnect the relay (behind PS kick panel) to be sure.

I have the replacement relay, haven't put it in yet - I've been pulling the dome fuse if she sits for a while.

 

[justacruiser]

Check the little mehcanical sensor/switch on the door frame that turns on the light when you open a door. If the switch went bad it might be creating an open circuit, as if the door were open all the time.

 

[Francinoman]

I have a very similar problem. I have a 24v 1988 62 series and the batteries loose all charge after about 1 or 2 weeks. I've always just made sure I drive it frequently or turn off the isolated switch when not in use but this got me thinking...

I checked my dome fuse with a multi meter. The amp setting doesn't seem to be working but when a door is open there is 24 volts across the fuse. When all doors are shut, key is off and nothing is turned on (the dome light itself isn't on) there is still 23.5v across that fuse. Is this normal? Or could this be what is causing my battery drain?

Being a 24v system it's a bit of a pain to have to recharge both batteries completely before connecting it back up again...

 

[Devils Paw 80]

Pulled the bulb from the rear cargo light and the draw went away. The switch had been in the "off" position though. But, that light has rarely worked. There's got to be something amiss with the wiring in that run. Not sure it's worth fixing.

 

[Slow Left]

I checked my dome fuse with a multi meter. The amp setting doesn't seem to be working but when a door is open there is 24 volts across the fuse. When all doors are shut, key is off and nothing is turned on (the dome light itself isn't on) there is still 23.5v across that fuse. Is this normal? Or could this be what is causing my battery drain?

I don't think that measuring Voltage across an 'open' fuse is the correct measurement to identify a current leak (aka parasitic draw) and I will do my best to try and explain why.


DC (Direct Current) electrical systems (whether 12V or 24V) must obey Ohm's Law:

V = IR

where V is Volts (measured in Volts), I is current (measured in Amperes) and R is resistance (measured in Ohms)

Since the Voltage is a constant (either 12V or 24V), then Current (I) and Resistance (R) are inversely proportional (if one increases in value, the other must decrease...so that the product of the two always equals 12V or 24V or whatever voltage the DC system is spec'd out to be).

This means, if you measure Voltage across an open gap in the circuit (whether that gap is a result of an open switch or a pulled fuse), you should always read ~12V or 24V...since the one side of the open gap is connected to the +side of the battery (12V or 24V) and the other side of the gap is connected to ground (0V).
And since you are measuring Volts (not Current or Resistance), you have no idea how much of that 12V or 24V you are measuring is dedicated to the Current component of the product or how much is related to the Resistance component...so the measurement fails to tell you if there is a Current component 'leaking' through a closed switch.

I'll try to post up an additional explanation to follow up which electrical measurement is good for what diagnosis...

 

[JLH911]

@Slow Left What ever happened with this. I would like to know your method for finding a draw.

Thanks!

 

[Slow Left]

@Slow Left What ever happened with this. I would like to know your method for finding a draw.

Thanks!

These are tough to diagnose...it really depends on the circuit.

The first step is to try and isolate which circuit might be 'leaking' current. Since all the factory circuits run through the main fuse panel, you might begin by interrogating each circuit there.
Also, if any recent electrical work has been done, then that circuit would be suspect.

Has the battery in your vehicle been going flat after a day or so of not running it? Or what are the symptoms?

 

[JLH911]

Thanks for replying so quickly. Yeah, goes dead after about two days. I'm suspecting the dome light/carb fan circuit since the carb fan (when it's supposed to go on) keeps going on and off for about 15 minutes. Sometimes it doesn't go on at all and yes, the wire and terminal on the sensor are good. Also, the dome light isn't coming on when the door is open, so maybe it's the door switch causing it.

 

[Slow Left]

OK, so the battery is going dead after two days of sitting and not being recharged by the alternator.

Assuming that the battery is good (local auto parts stores will often offer free tests for both the battery and the alternator), then there is a short somewhere that is drawing power from the battery with the vehicle off.

Here is a wiki that shows the steps for how to test the OE circuits at the main fuse box:
http://www.wikihow.com/Find-a-Parasitic-Battery-Drain

With the engine OFF, if you disconnect the negative terminal of the battery and install an ammeter (capable of handling up to 20A) in line between the negative battery post and the negative battery cable you just removed. If the ammeter is showing more than 25-50 mA (milli Amperes), then there is indeed a short somewhere in a circuit.
If you remove a fuse at a time at the main fuse box, then the circuit that shows a drop down towards 0 A with it's fuse removed is going to be the suspect circuit.
A short in the voltage regulator on the alternator might also be the cause, so if you disconnect the low voltage wires to the alternator (just like you did for the fuses) and reading on the ammeter drops towards 0, then most likely a bad voltage regulator on the alternator.

The Dome fuse circuit that runs the cooling fan and the dome lights is not switched through the ignition switch, so it is 'hot' even when the engine is off...so a short here would certainly drain the battery.

Do you have a multi-meter that can read up to 20A?

 

[JLH911]

Just saw a similar way of hunting a parasitic battery drain on YT. Showed pretty much what you've laid out. Thanks. Will report back my findings. Oh, and Yes, I have a nice FLUKE DVM.

 

[Slow Left]

Just saw a similar way of hunting a parasitic battery drain on YT. Showed pretty much what you've laid out. Thanks. Will report back my findings.

Yeah, after you run this test, if you identify the circuit that is causing the drain, then post back up and I'll do my best to help you troubleshoot that circuit further.

Keep in mind that when you connect the ammeter in line like that, you don't want to let either of the two connections ground onto the chassis. The contact at the battery terminal shouldn't be able to (physically), but the connection onto the end of the negative battery cable might be able to.
In this case, it probably wouldn't be a safety issue because you are connecting to the ground side of the circuit anyhow (not the positive, 'hot' side) and with the engine off and the key out of of the ignition, no current should be flowing through the circuits (that is why if you do see a ~25-50 mA current reading on the ammeter, there is a short).

But in general, amps (current) kill, not volts. In the FSM there is a on-vehicle procedure for testing the high Amp alternator circuit (the one that charges the battery while the vehicle is running) which calls for installing the ammeter in-line between the alternator and the battery...on that test, you most certainly don't want to let a connection touch ground (or yourself be in the path to ground by accidentally touching an uninsulated connection)...those alternators are kicking out some serious current.

Here, on the other hand, the vehicle is off and you are not testing the high amp circuit on the alternator...but you should still train yourself to approach it as if it were a high amp circuit and not let the connections touch ground.

 

[JLH911]

(that is why if you do see a ~25-50 mA current reading on the ammeter, there is a short).

Do you mean a reading greater than the 25-50mA or around 25-50. I know the ~ means around, but just want to make sure.

 

[Slow Left]

I don't think that measuring Voltage across an 'open' fuse is the correct measurement to identify a current leak (aka parasitic draw) and I will do my best to try and explain why.

The guy in this video does a decent job explain the behavior of a DC series circuit and why, in the case of trying to identify 'parasitic draw' (i.e. current drain) in the circuit, measuring for current (as opposed to voltage) is preferable...since the current of an 'off' circuit should read 0 amperes and the current of an 'on' circuit will be the same throughout the circuit. So, if you get a current measurement on an 'off' circuit, then there is a 'leak' somewhere and current is being allowed to pass through the circuit when it should not be.

But voltage can vary along the series circuit depending on the components of the circuit...so measuring current is simpler in the case of hunting down a 'leak' in the circuit.



He's an electrical engineer, so the video is about as exciting as one would expect, but he explains it well...and in an British (I think) accent, too, so that's kind of a bonus if just to change things up and give this whole thing more of an international feel...unless you happen to be British, then it is probably just ho-hum...just another day of videos on DC circuits in my shared language...no biggie...

 

[Slow Left]

Do you mean a reading greater than the 25-50mA or around 25-50. I know the ~ means around, but just want to make sure.

Yes, ~ means around...so I'm saying if you see a reading of 50 mA then that is sufficient current to be considered a 'leak'. If you read 5 mA, then that is probably not enough to be considered a leak.

mA stands for milli Ampere

1 mA = 0.001 Ampere (1 mA is three orders of magnitude less than 1 A)

then

50 mA = 0.050 Amperes

The fuses in the main fuse box are rated for 10, 15, 20 or even 30 A, so the current flowing through these circuits you are testing when they are on is much much greater than the amount of current you will be measuring that is 'leaking' when the circuit is off.

An also remember, when you first hook up the ammeter in-line on the negative side of battery (between the neg post and the removed neg battery cable), if you see a reading of say 30 mA (milli Amperes), that indicates that there is enough current 'leaking' out of the a closed circuit to cause the battery to drain. Then, as you remove each fuse at the main fuse box, if you see that value of 30 mA drop towards 0 ( so say with the fuse to the Dome circuit removed, the ammeter now reads 5 mA), then that tells you that the Dome circuit was the cause for the 'leak'.
Because you have removed the fuse, you have broken the path and current can no longer 'leak' through that circuit, so your current reading drops towards 0...