truck electrical problem

This is where I am. I have quite a few of accessories on my truck, lights, amp/subs etc, and I have a draw. This is not a normal draw from what I can come up with, talked with a couple different mechanics everyone says to start pulling fuses, well I have. I have a diesel so two batteries, pulled both neg. straps, put a test light from the strap to the post to do the "drain test". Well, on a normal drain its a steady dim or bright light, mine is different. It starts really bright and within two seconds or so goes dim to nothing. I have pulled every fuse on the truck, relay powers, and still just have that bright to dim affect. Anyone ever seen this or can explain to me what is going on? Checked the alt, batteries are new and charged, im lost thanks for any help. Kevin

What kind of truck? This may be normal. It could be the ECU going to sleep or an accessory powering down.

For starters, throw your test light back in your tool box and buy a digital volt meter that can handle a minimum of 10 amps when hooked up to measure current. Get yourseld a battery shunt or shut off tool that can work with your style batteries (either top post or side post). Temporarily disconnect one battery and make sure the remaining one is fully charge. You need to disconnect it from the vehicle and use a proper battery charger before making any tests. After you have the battery charged and reconnected, install the shunt inline in the negative terminal. Close the shunt to allow current to flow. If you have done it correctly the interior lights and such will still work. Shut off all possible draw sources such as cigarette light power adaptors and such. Connect your meter to each side of the shunt and set it up to measure amperage. With the shunt closed you should see virtully no reading on your meter. Open the shunt so all current flows through you meter. You may have to wait for a few minutes, up to a few hours for all things in your vehicle to completely shut down. Modern vehicles are like this and may look they are off but aren't. Take a reading after 2 hours once the reading is stabalized. If it is more than 50 ma (milli amps) you have too high a draw. Ideally, the reading wwould be better if it were closer to 20 ma. If the reading is high then one by one start disconecting suspect circuit which you have added. Only do one at a time and then recheck the reading. Most of your equipment will consume power, but you need to find the one that is creating the biggest problem. If all your equipment checks out OK, then start removing one fuse at a time from the factory fuse boxes to check the remainder of the vehicle. It may also be neccessary to disconnect the starter solenoid and alternator in the process, as these are not usually fused. It is a good idea to disconnect any door jamb switches before you start to keep the doors open while checking things.sparky

A capacitor....

sparkie wrote: For starters, throw your test light back in your tool box and buy a digital volt meter that can handle a minimum of 10 amps when hooked up to measure current. Get yourseld a battery shunt or shut off tool that can work with your style batteries (either top post or side post). Temporarily disconnect one battery and make sure the remaining one is fully charge. You need to disconnect it from the vehicle and use a proper battery charger before making any tests. After you have the battery charged and reconnected, install the shunt inline in the negative terminal. Close the shunt to allow current to flow. If you have done it correctly the interior lights and such will still work. Shut off all possible draw sources such as cigarette light power adaptors and such. Connect your meter to each side of the shunt and set it up to measure amperage. With the shunt closed you should see virtully no reading on your meter. Open the shunt so all current flows through you meter. You may have to wait for a few minutes, up to a few hours for all things in your vehicle to completely shut down. Modern vehicles are like this and may look they are off but aren't. Take a reading after 2 hours once the reading is stabalized. If it is more than 50 ma (milli amps) you have too high a draw. Ideally, the reading wwould be better if it were closer to 20 ma. If the reading is high then one by one start disconecting suspect circuit which you have added. Only do one at a time and then recheck the reading. Most of your equipment will consume power, but you need to find the one that is creating the biggest problem. If all your equipment checks out OK, then start removing one fuse at a time from the factory fuse boxes to check the remainder of the vehicle. It may also be neccessary to disconnect the starter solenoid and alternator in the process, as these are not usually fused. It is a good idea to disconnect any door jamb switches before you start to keep the doors open while checking things.

Thank you very much sparkie, I will hopefully get to this tomarro night. I started digging through my stuff and found This , is this adequate to use or should I buy something different? Sorry I have never used a multimeter so new to this

I can't find the rating for DC current on that listing. It is usually a # just above the port for the lead at the bottom left of the meter. If it is the # 10, then it should work OK. Read the manual for the meter and it will show you which settings to use to safely measure DC current. It will also tell you how to interprut the readings. Understanding where the decimal is on the reading makes an enormus difference.sparky

Nothing wrong with a test light for quick and dirty, that brightness could be a fade-away dome light. With charged batteries, depending on make and year you should be drawing 40-60 milliamps. Or as my antipodean buddy suggests, an amp capacitor or condenser depending on where you live.