Positive power passing through chassis
Thread Starter
2nd Gear
Joined: Jun 2013
Posts: 2
Likes: 0
From: Davao City
Positive power passing through chassis
Hi Guys
Decided to sign up after being lost for direction. I have a 1988 Corvette L98... Just recently the battery has been draining completely and would not charge after starting. I swapped it out with a brand new battery wich started no problem and seemed to be charging... the volt meter ranged from 11.6 volts when braking, ac, flashers etc to 13.1 idling. I know its supposed to be 13.9...
Thenew battery is also draining or close to dead during starting, I disconnected negative terminal and put a test light from the negative terminal of battery to chassis of car. It lights up. This shows that positive power is passing through engine block and chassis when only the negative terminal is disconnected. Is this normal?
I would assume it would cause a short but no fuses are blown.
I also tried to disconnect the socket of alternator and the red + wire but positive power still running through block.
Any suggestions?
Decided to sign up after being lost for direction. I have a 1988 Corvette L98... Just recently the battery has been draining completely and would not charge after starting. I swapped it out with a brand new battery wich started no problem and seemed to be charging... the volt meter ranged from 11.6 volts when braking, ac, flashers etc to 13.1 idling. I know its supposed to be 13.9...
Thenew battery is also draining or close to dead during starting, I disconnected negative terminal and put a test light from the negative terminal of battery to chassis of car. It lights up. This shows that positive power is passing through engine block and chassis when only the negative terminal is disconnected. Is this normal?
I would assume it would cause a short but no fuses are blown.
I also tried to disconnect the socket of alternator and the red + wire but positive power still running through block.
Any suggestions?
Safety Car
Joined: Aug 2002
Posts: 3,842
Likes: 230
From: SANTA CRUZ CA
Disconnect one of the batt cables, and place an ammeter between the cable end and the batt post. Check the amp reading........ should be about 30-60 ma.
If amps exceed the milliamp example, you might pull one fuse at a time to determine if there is a parasitic charge. If the amps drop when a particular fuse is pulled, you have achieved part of the process..
Many fuses protect several circuits, so circuit investigation may be required.
Re your batt charge numbers........ you should see 14.3V (+/-) after start-up, and then 14.0V (+/-) after about 10 minutes.
You might have the alternator checked under load...... usually free at many auto stores.
If amps exceed the milliamp example, you might pull one fuse at a time to determine if there is a parasitic charge. If the amps drop when a particular fuse is pulled, you have achieved part of the process..
Many fuses protect several circuits, so circuit investigation may be required.
Re your batt charge numbers........ you should see 14.3V (+/-) after start-up, and then 14.0V (+/-) after about 10 minutes.
You might have the alternator checked under load...... usually free at many auto stores.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The battery is a series circuit. From the battery + terminal to the various electrical items and then back through the engine block and frame to the negative terminal. It doesn't matter where you break the circuit to measure current.
There are several circuits that are "on all the time". ECM, radio, dashboard, C68 HVAC controller. You will always see a small current draw because of these guys.
The problems happen when the current is more than it should be. The only way to find out is to measure it with a meter.
There are several circuits that are "on all the time". ECM, radio, dashboard, C68 HVAC controller. You will always see a small current draw because of these guys.
The problems happen when the current is more than it should be. The only way to find out is to measure it with a meter.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
There are circuits that are powered up when the car is sitting. A small drain of anywhere from 15 to 30 milliamps would be normal. At that rate, the battery should be able to easily start the car after sitting for a month, maybe 6 weeks.
You should check for a battery draw using a digital volt/ohm meter. Also check the voltage output at the alternator terminal (where the large red wire connects. I'm thinking the alternator is bad. Fully charge the battery, then start the engine and check alternator voltage output at the alternator. Your reading are way too low.
A fully charged battery will show something like 12.8v across the battery terminals. When the engine is started, you should see something like 14.1 to 14.3v at the battery. As the alternator returns the charge to the battery, you should see something like 13.6 to 13.8v.
You should check for a battery draw using a digital volt/ohm meter. Also check the voltage output at the alternator terminal (where the large red wire connects. I'm thinking the alternator is bad. Fully charge the battery, then start the engine and check alternator voltage output at the alternator. Your reading are way too low.
A fully charged battery will show something like 12.8v across the battery terminals. When the engine is started, you should see something like 14.1 to 14.3v at the battery. As the alternator returns the charge to the battery, you should see something like 13.6 to 13.8v.
Thread Starter
2nd Gear
Joined: Jun 2013
Posts: 2
Likes: 0
From: Davao City
Thank you very much guys, I did not do the meter test yet but as I'm seeing its normal for the + from the battery to jump onto the engine block with the negative terminal diconnected?
I tried removing all the fuses 1 by 1 and the test light dimms when I remove clk/sys... However it still has power running to the block.
I do not have a meter handy, but I have a digital battery tester that states 13.5v at battery terminal. This is a new alternator but I had a cousin purchase it, I am not in the US. How I wish I could go down to the parts store and get it tested, dont have that kind of convenience in asia.
I will be working on the car this weekend, off to buy a multimeter... Thank you, I have a direction, I will update on my findings...
I tried removing all the fuses 1 by 1 and the test light dimms when I remove clk/sys... However it still has power running to the block.
I do not have a meter handy, but I have a digital battery tester that states 13.5v at battery terminal. This is a new alternator but I had a cousin purchase it, I am not in the US. How I wish I could go down to the parts store and get it tested, dont have that kind of convenience in asia.
I will be working on the car this weekend, off to buy a multimeter... Thank you, I have a direction, I will update on my findings...
