I need electrical help
 

I need some help. I chased down a small current drain on my 65 and it turned out to be the aftermarket radio I had installed. No big deal, I just changed the wire for memory over to the switched radio connector so that it only holds memory when the key is on. I never listen to the radio anyway, so I"m ok with that.

Here's where I need help. While checking current draw with the negative battery lead disconnected and an ammeter in series with the negative post and the disconnected negative cable, what current should I read if I turn ignition to ON? I've never checked that before, and mine reads 4.6 amps. That seems high to me. It only reads 6.5 amps when the backup lights are on in addition. With the key in off position, I'm getting .001 amps, and in acc I'm getting about 1 amp. I know the key supplies voltage to the coil, and to the alternator, but everything else is off. Has anyone ever done that test before, checking draw with key ON?
When I turn the key to ON the battery gauge on the dash moves to the negative very slightly, but not much and I would expect that. Where are the 4 amps going?

Just FYI, I also have Classic Auto Air, Detroit Speed head light conversion, and 4 way flasher added. The headlight conversion works with the key off, so I don't think that's an issue since it's not drawing at all with the key off. I checked the courtesy lights and the glove box light and all are off. Any ideas? Maybe it's normal?

Current Draw
 

Hi 65GGVERT,

Assuming your battery is roughly at 12 volts, the primary resistance of your coil is .5 ohms, the ballast resistor is about 2 ohms, and the resistance across the points is .1 ohm, 4.6 amps is right on the nose.. 12 volts divided by 2.6 ohms equals about 4.6 amps.


RON

I guess I should have bumped it to see if the points were closed, thought about it but didn't want to blow my 10a meter. I'll check it to see if they're closed. Thanks.

Is not the alternator field coil (rotor) hot with ignition on?

Dan

I guess I'll check that next. With points open I'm still getting almost 5 amps with key on.

Depending on the amp rating of the alternator you field draw could be from 2-5A. Disconnect the two wire plug at the back of the alternator and see if the amps drop off.
Joe

I disconnected the red wire, no change, didn't try the plug. I'll do that next time out. The battery gauge in the dash just barely twitches when I turn the ignition on, just like they usually do. Reads positive when I start it.. I just never measured current with the battery disconnected and switch on before.

Disconnected the plug from the alternator and the current dropped very slightly to 3.9 amp. I have a friend with the same car, I'll measure his next time I'm over.

I work on these cars and I think you are chasing a ghost. A few amps at key on is fine. Gauges and senders have to be powered. Alternator, regulator, etc. When you said in your post that you turned the key on I was expecting the fuse in the meter to pop. It more than likely would on a modern car many of which don't use a battery that is much bigger than what is correct for your 65. I wouldn't worry about it, its in the range of normal.

LOL!!! I was thinking the same thing. 65GGvert is the "go to" guy for electrical issues. Let us all know if it turns out to be an "issue" or is completely normal.

Thanks, I've never had a reason to measure current with the key on before, and shouldn't have this time. The b/u lamps only drew 2 additional amps, so it made me curious what would draw 4 amps. I can sure see how leaving the switch on runs the battery down. The ballast is getting hot, so I'm going to assume it's passing through there and forget about it. I don't think the gauges or fuel sending unit all together would draw that much, and I don't see a path to ground when the points are open for the ballast. The fact that the battery gauge barely moves like normal also makes me think probably all my cars have done this and I never knew it.
Thank you to those who responded, I appreciate it. I'll still measure the friend's 65 sometime this week since it's sitting with the battery cutoff open and all I need to do is clip on the ammeter, but I think you're right about it being normal.

Funny you mention the fuse. I did pop the 300 ma meter circuit fuse when I connected because I forgot the Detroit Speed headlight actuators would reset when the current passed through the meter and completed the circuit. I was using the 10 amp meter circuit after that, so that fuse was ok. Just glad I didn't bump the starter to move the points without disconnecting and closing the shutoff.

[QUOTE=65GGvert;1597613871 The b/u lamps only drew 2 additional amps, so it made me curious what would draw 4 amps...….but I think you're right about it being normal.[/QUOTE]

The alternator field coil came to mind as it goes hot with key on (as does the field relay coil in the regulator). 4 amps isn't much given 12 volts (but you knew that). I might have been just as curious as you!

Dan

You know this is funny, I have not been here for a very long time, but it would be hard to deny that 65GGvert has his s--t together when it comes to electrical issues. it reminds me of the time someone checking AC voltage decided to switch the fluke meter to DC and measured 12 volts DC on an AC system, when asked why he did it he said he wanted to see what it would measure if anything at all. but that's a very long story. it turned out that there was 12 volts DC running along the neutrals on an AC system.

A great way to check for diodes on the way out is to set the DVM to AC volts and go across the battery, but you probably knew that too!

Dan

yea you and me both

I was curious so I looked at the key on draw of 70 which is the closest I could get with whats in the shop right now. Very similar electrically except the 70 has some minor differences. And, the 70 had 7.5 amps draw at key on with everything off. It just got me curious as well so I thought I'd share what I got off of a similar car with no known electrical issues.

**Wanted to correct this. 80 is the first year of the computer. We have one in the shop with issues related to the computer and just got my wires crossed early morning."**

Thank you very much for checking. I had a 70 and a 72, but there weren't any computers on board that I'm aware of. You have been a great help and I appreciate it.

No you're absolutely right. We've got an 80 in the shop also and got my wires crossed for a second. Didn't even cross my mind until I read your comment. Coffee needs to kick in. 80 is the first year of the computer.