fj62 dome light circuit parasitic draw
- Thread starter Devils Paw 80
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
Here's a video on how to use a multi-meter to take continuity, resistance, voltage and current measurements on DC circuits. Again, narrated by an Electrical Engineer...but at least he is wearing a suit...
BTW, that site in general looks like it has good tutorials on DC circuits.
@gregnash : notice how the multi-meter he uses uses the same function for measuring continuity and resistance (continuity = 1/resistance)...and that when taking continuity or resistance measurements, the power supply must be detached from the circuit (because the multi-meter generates it's own current to send out through the circuit when taking a continuity or resistance measurement)...
http://mods-n-hacks.wonderhowto.com...tance-and-continuity-using-multimeter-422502/
EDIT: here's a more detailed set of tutorials on taking measurements with a multimeter...narrator appears to be South African, so everything might be upside down
BTW, that site in general looks like it has good tutorials on DC circuits.
@gregnash : notice how the multi-meter he uses uses the same function for measuring continuity and resistance (continuity = 1/resistance)...and that when taking continuity or resistance measurements, the power supply must be detached from the circuit (because the multi-meter generates it's own current to send out through the circuit when taking a continuity or resistance measurement)...
http://mods-n-hacks.wonderhowto.com...tance-and-continuity-using-multimeter-422502/
EDIT: here's a more detailed set of tutorials on taking measurements with a multimeter...narrator appears to be South African, so everything might be upside down
Last edited:
I have outlined the circuit(s) for the Dome Lights, Carb Cooling Fan and Alternator in the wiring diagram (split in two images) below.
NOTE: This is the wiring diagram for the 60 and in reference to the 60...the OP on this thread had originally inquired about the 62, but this addresses similar symptoms but in a 60...
Notice that all of these circuits share a common fusible link (labeled #3 in the image) coming off the battery. That fusible link does not pass through the ignition switch, so even with the engine off and the key out of the ignition, all the components on the circuits behind that fusible link 'see' 12V+.
That means, with engine off and key out of ignition, if there is a short in any of those circuits, then it will draw current from the battery.
A short meaning a 'shorter' path to ground than through the designed path of the circuit. In order to current to flow, there must be a continuous 'downhill' path to ground.
The top of the hill in this case is the 12V+ potential at the positive terminal of the battery.
The only time any current should be allowed to flow from this highest 12V+ potential at the positive terminal of the battery is when you do something that closes a switch, and when you close that switch you complete the path to ground.
Notice that ALL paths (circuits) on the wiring diagram end up at ground, but current will only be allowed to flow through that particular circuit when you close the switch that completes the path on that particular circuit.
The short is a failure in the circuit (a broken wire, a malfunctioning component like a switch or a relay) that touches ground (chassis or body) in a place along the path of the circuit that it should not be touching ground.
If there is a short on a circuit behind fusible link #3 (also #1 for that matter - the headlights/running lights), it will drain the battery even with the engine off and key out (for the reason I explained above).
The reason why hooking up an ammeter in-line between the negative battery terminal and negative battery cable works is that it can read that 'leaky' current as it travels back to the negative battery terminal, because all circuits go to ground (body/chassis) and the negative cable is also attached to ground (body/chassis).
Remember, the vehicle stands on rubber tires that are insulators.
So, when the short allows current to flow from the highest 12V+ potential at the positive battery post, out through fusible link #3 (for example), down the particular circuit behind that fusible link, through the main fuse of that circuit and to the body/chassis through the short contact....you can measure that current as it travels back to the neg terminal on the battery because it can't travel literally to the ground (Mother earth...Pachamama) because it can't travel through the tires.
And when you pull the main fuse on the circuit that is shorting, it stops the flow of current along the path of that circuit...and that is why you should see the ammeter value drop.
HTH
Last edited:
So here's what I found. I have a Blue Sea auxiliary fuse box installed for my CB, Ham Radio and Car stereo. When I hooked up my DVM inline, I had a reading of about 50mA. I removed the the 15amp fuses to the three aforementioned devices and the amp draw dropped to 30mA. Still a "leak" as you call it.
So I pulled some more fuses from the factory underdash fuse panel and when I got to the fuse for the "Horn/hazard lights" it dropped to almost zero mA. So there you have it. I have to troubleshoot that circuit now.
Thanks for posting up that info. When I get some time to troubleshoot some more, I'll report back.
So I pulled some more fuses from the factory underdash fuse panel and when I got to the fuse for the "Horn/hazard lights" it dropped to almost zero mA. So there you have it. I have to troubleshoot that circuit now.
Thanks for posting up that info. When I get some time to troubleshoot some more, I'll report back.
Nice.
Sounds like it might be a combination of circuits, but since the "Horn/Hazard" circuit gave you the biggest drop, sounds like a good place to start.
Notice on the wiring diagram that the "Horn/Hazard" circuit runs behind fusible link #1 (not the #3 link I highlighted above), which also doesn't pass through the ignition switch.
Behind the "Horn/Hazard" fuse, there are the 2 horns and the horn switch (the pin and plate on the steering wheel)...but there is also a connection to the Hazard switch and multiple components behind that switch (flasher relay, turn signal switch and all the signal lights)...so if there is a short in that Hazard switch and a malfunctioning component behind it, then it might be allowing current to be drawn from fusible link #1 to ground through that/those shorts....
Chassis-Body FSM should have procedures for testing the relays and switches. Broken wires at lights (running lights especially) that ground to the body are also common sources for shorts...but light shorts usually blow fuses and because of the circuit, there would have to be a short in the hazard switch too in order for a light to be causing this.
I would work back from the "Horn/Hazard" fuse, testing the components.
For the horns, you should be able to disconnnect the wire connector at each horn and then test for continuity (resistance) through the two contacts on connector on the horn side. No continuity (or a reading of infinity for resistance) means a short...and continuity (or reading of close to 0 ohms resistance) means a circuit in good working order.
The horn switch is a mechanical switch.
Next back would be the Hazard switch. I'll bet the FSM has a procedure for testing that one...
Last edited:
@JLH911 , you might have already thought of this, but a quick, low cost test you could run to confirm that the current leak is coming from the Horn/Hazard and/or the aftermarket radio circuit(s) is to pull each of the fuses from the suspect circuits one at a time and let the vehicle sit for those couple of days on a fully charged battery and then see if the battery holds it's charge with those fuses out...
Just a clarification: Tires have nothing to do with the circuit. The neg pole of the battery is connected to the frame, so ground is the frame, anything metal connected to the frame, or any wire that goes to the neg terminal. i.e. the return path to the battery. Not literally "the ground". If the tires were metal it would work the same. Glad they are not.
Thanks for rephrasing that Jaw...that's what I was trying to communicate but I guess it didn't quite get the point across...
EDIT: Hang on a second, I think I missed the point you were trying to make about the tires and the circuit, Jaw...
No, if the chassis/body of the vehicle were actually touching the ground (with either metal wheels or with a disconnected ground wire touching the dirt), then I do not think that you would be able to read a 50 mA current leak with a multimeter installed inline between the negative battery post and the disconnected battery cable...in other words, this trick for identifying a current leak would not work.
But easy enough to convince yourself, although I think it would be easier to run a wire from the frame to the dirt than to find and install metal wheels...
The reason why I don't think it would work is because current will always flow down the path of least resistance (to reach it's lowest energy state...which in this case is potential energy or volts).
And if the 'metal wheels' provide a path of least resistance, then the current will flow there and into the earth where it will dissipate...and you will not be able to read that current with the multimeter installed inline at between the neg battery post and cable because the current won't be flowing there...it will be flowing into the ground.
The point I was trying to make about the tires isolating the chassis/body from earth is better phrased by Jaw's post...that the chassis/body is actually part of the circuit (because it is isolated) because all circuits tie into it as a 'ground' as does the negative post on the battery.
Last edited:
You should see the switches for the front dome light in each of the door jambs. I think there is a thread about cleaning those contacts, but you'll have to do a search to find it.
I just ran across the thread for cleaning the ground on the dome light in the rear cargo area:
https://forum.ih8mud.com/threads/how-to-tailgate-light-switch-restore.679368/
Remember that those switches in the door jambs 'close' when you open the door. So, if the contacts on the switch are dirty, when you open the door and the switch closes, it doesn't make good contact and the circuit doesn't close (i.e. poor path to ground) as it should, so current will not flow and the light will not shine...
I'm a little confused. There was a 50mA draw. This means it would take 20 hours to equal 1 AH (amp hour). I thought the typical car battery has at least 40AH of capacity. Don't see how 50mA would drain a battery in two days.
The curve is probably non-linear. As the battery drains and looses power, the "AH" calculation will also lower. Condition of the battery could also come into play...like if the battery wasn't fully charged to begin with.
But it would be easy enough to set-up and run a test to convince yourself how long it would take to drain the battery on your vehicle to the point that it won't start.
But it would be easy enough to set-up and run a test to convince yourself how long it would take to drain the battery on your vehicle to the point that it won't start.
Another consideration is that even is the battery is old(er) and no longer meets it's Ah rating, the battery only has to loose enough power so that the starter motor can't draw enough current to run...in other words, the 'parasitic draw' doesn't have to entirely drain the battery in order to play it's role as a spoiler...just enough that you can't start the vehicle...
The Ah rating is for a specific amount of current over a specific amount of time.
For example, a manufacturer might rate it's 50 Ah battery as being able to draw 5 Amperes for 10 hours.
50 Ah x 12 V = 600 Wh (Watt hours) = ~2 x 10^6 Ws (Watt seconds)
The starter motor draws 1 kW, if it is completely efficient...which it isn't, so let's say it's 75% efficient and draws 1.5 kW (125 Amperes at 12 Volts).
Then a 50 Ah battery is rated to run a 1.5 kW motor for ~14.5 seconds (that's assuming a linear relationship between the 50 Ah rating at 5 A for 10 hrs the 125 Amperes the starter draws).
If the battery voltage drops from 12V to 10V, then that same calculation for a 50 Ah battery is now rated to run a 1.5 kW motor for ~12 seconds.
How much power would the battery have to loose then over a 2 day period in order for the vehicle not to start? ...and is a 50 mA continuous loss sufficient over a 2 day period in order to meet that threshold?
...don't know but there are a ton of assumptions here.
The Ah rating is for a specific amount of current over a specific amount of time.
For example, a manufacturer might rate it's 50 Ah battery as being able to draw 5 Amperes for 10 hours.
50 Ah x 12 V = 600 Wh (Watt hours) = ~2 x 10^6 Ws (Watt seconds)
The starter motor draws 1 kW, if it is completely efficient...which it isn't, so let's say it's 75% efficient and draws 1.5 kW (125 Amperes at 12 Volts).
Then a 50 Ah battery is rated to run a 1.5 kW motor for ~14.5 seconds (that's assuming a linear relationship between the 50 Ah rating at 5 A for 10 hrs the 125 Amperes the starter draws).
If the battery voltage drops from 12V to 10V, then that same calculation for a 50 Ah battery is now rated to run a 1.5 kW motor for ~12 seconds.
How much power would the battery have to loose then over a 2 day period in order for the vehicle not to start? ...and is a 50 mA continuous loss sufficient over a 2 day period in order to meet that threshold?
...don't know but there are a ton of assumptions here.
Last edited:
Any luck on this? Are you still seeing a battery drain?
Having the same issues and wondering the same..
Have you been able to narrow it down to a specific circuit(s)?...by pulling the fuses at the fuse box with the ammeter installed in line between the neg battery post and neg battery cable?
I think I found the issue, the dome light fuse, but my meter doesn't seem to be working properly...so until I can figure that out I can't be sure.
- Thread starter
- #38
Did I miss your tips on doing this? Turns out pulling the rear dome light didn't solve my problem. The draw is definitely in the dome light circuit. I've had the fuse pulled for a few months now..
No, I don't think the troubleshooting with JLH911 got into working through the Dome circuit itself...which means we didn't find a solution yet or reveal any tips/best practices on how to approach troubleshooting the Dome circuit (once it has been identified as a source of a parastic draw).Did I miss your tips on doing this? Turns out pulling the rear dome light didn't solve my problem. The draw is definitely in the dome light circuit. I've had the fuse pulled for a few months now..
Sooooo,....looks like it's about to get messy and gonna have to think...
JLH911 has a 60...and the Dome light circuit is different for the 60 and 62 (the 62 has a clock)
89GASHOG (I think) and EastCanFJ62 have a 62...and since the OP of the thread is 89GASHOG, and EastCanFJ62 seems to have the same problem, then maybe the best way to approach it is to continue working through the 62 troubleshooting on the Dome circuit.
89GASHOG, when you say "...pulling the rear dome light", did you just pull the bulb or did you disconnect wires going to and from the rear light fixture?
- Thread starter
- #40
Just pulled the light out (Yes, it's a 62). Should I try removing the fixture? It's never worked properly for me anyway...