1968 Current Drain Problem

[Paul P.]

All:

What would the expected current drain with the ignition switch off, doors closed, on a '68 convertible be?

Some background: I recently replaced the clock with an aftermarket unit. The new clock worked and the car started. About five days later I went to drive it to work and the (new) battery was completely dead. The clock wasn't even working as there was no voltage in the system.

After charging the battery I pulled the negative terminal and measured the current - approximately three amps!! That's way more than I would think it should be. I immediately suspected the new clock and removed it. But I still have around three amps of current draw, even with the ignition off and the doors closed.

I am now in trying to solve the problem by the ol' process of elimination. I have disconnected the factory alarm relay and the modern digital aftermarket radio (I do NOT trust those things!) along with the battery connection to the alternator. I also disconnected the gauges in the center console.

Does my '68 convertible have interior lights that go on when the doors are opened? Sorry for the dumb question but I don't recall seeing them and I am new to the car. It's too bright of a day now for me to give it a visual test. I know the center "glove box" compartment behind the seats has one but that one I can see but I can also witness a current difference of about .5 amps when I switch if off and on, so I know that isn't the problem. I can see the current increase to around 10 amps when I turn on the parking lights, so it is not like they are somehow accidentally on.

I do have a good DMM and an electronics background in my favor. I am considering pulling fuses one by one to see if the problem cab be further isolated.

As a matter of reference, my 1990 Mazda manual specified .020 amps of what they call "dark current". I had the chance to measure it and it was .005 amps.

Any ideas? I may start pulling fuses one by one to see if I can find the culprit, but am hoping to find a solution before resorting to that. I keep thinking that this problem only occurred after I replaced the clock, so I may have messed up something in the center instrument panel area. Before that I was able to go a week or two of inactivity and be able to start the car without a problem.

[Jim T.]

Re: 1968 Current Drain Problem

Paul I am long time owner of 1968 convertible, unplug the center "glove box " light. Mine has been disconnected for over thirty years. Next up is the windshield wiper switch. Start the car and turn on the windshield wipers, wet the windshield if you like, and let them do at least one swipe and using the windshield wiper switch turn off the windshield wipers. Now test for a current draw?
Reason I mention the wiper switch is that if my wiper switch is " accidentally" turned on/off when the car is not running it will pull current until the car is started and the wiper switch is used to cycle the windshield wipers on/off.
There is a inline plastic connection that is accessible from the jack storage area that I use to disable the glove box light from working.

[Larry M.]

Re: 1968 Current Drain Problem

Paul:

I measured 54 ma parasitic current draw on my 1967 convertible with original factory wiring. I read somewhere that less than 80 ma was acceptable (but somewhat high). I thought even 54 was a bit much. A good battery disconnect switch lowers this number down to zero.

Larry

[Paul P.]

Re: 1968 Current Drain Problem

Jim:

As my ~30 year old cubical neighbor at the day job might say: "YOU DA MAN!!!"

It was exactly as you described. Cycling the wiper motor brought it all under control.

Funny thing is, while I was working on the instrument console I noticed a bulb socket without a bulb. I didn't think much of it, figured it had been lost in the past or I had fumbled it loose. Since I had a spare I installed it. When it was all back together and I turned the key to the on position, a "WIPER O'RIDE" idiot light came on in the spot I had installed the bulb. I knew then that the problem was solved. Too bad the bulb hadn't been there all along, I could have saved myself some frustration.

Parasitic current is now around .030 amps, about what I would expect since it includes a modern digital radio (not my idea, no flames please) with it's memory requirements.

Thanks Jim for your prompt and excellent reply. Should you be in the Los Angeles area consider yourself do be due a beverage of your choice.

Now going for a celebration ride.

~paul

Next up is the windshield wiper switch. Start the car and turn on the windshield wipers, wet the windshield if you like, and let them do at least one swipe and using the windshield wiper switch turn off the windshield wipers. Now test for a current draw?
Reason I mention the wiper switch is that if my wiper switch is " accidentally" turned on/off when the car is not running it will pull current until the car is started and the wiper switch is used to cycle the windshield wipers on/off.
There is a inline plastic connection that is accessible from the jack storage area that I use to disable the glove box light from working.

[Jim T.]

Re: 1968 Current Drain Problem

Paul good to hear that the wiper switch was the problem area. My 68's original glove box cover/lid is hard plastic (FEB built) and is not flat/straight enough any more to keep the glove box light off when the door is closed. This is why the switch was disconnected. Your convertible should have three interior lights, rotate your light switch counter-clock-wise and this action should illuminate a light in the cargo area near the drivers side spring/hinge that supports the deck lid. The other two lights are also exposed light bulbs in holders for the drivers and passengers foot well. The switches in the front of each door opening controls the illumination of interior lights when the light switch is not used for this illumination.
Our 68 does not have the "Wiper O'Ride" light. If the wiper electrical switch mounted at the bottom of the steering column that stops the wipers over the windshield so the wipers can be cleaned or changed should always be in the off position unless it is being used for wiper maintenance in stopping the wiper action.

[Paul P.]

Re: 1968 Current Drain Problem

My '68 is a late July build. It still has the glove box light functional but I'll be aware that the switch can go awry. I now see the interior lights but they do not work, something I'll have to look into. In my case the wiper switch near the steering column is the only way I can get the wipers to function - the switch at the top of the center instrument cluster does not work. It's always something with cars of this nature, is that part of their charm?

Thanks again for your excellent help.



Regards,


Paul Pollock
WebCars! Webmaster
http://web-cars.com

Paul good to hear that the wiper switch was the problem area. My 68's original glove box cover/lid is hard plastic (FEB built) and is not flat/straight enough any more to keep the glove box light off when the door is closed. This is why the switch was disconnected. Your convertible should have three interior lights, rotate your light switch counter-clock-wise and this action should illuminate a light in the cargo area near the drivers side spring/hinge that supports the deck lid. The other two lights are also exposed light bulbs in holders for the drivers and passengers foot well. The switches in the front of each door opening controls the illumination of interior lights when the light switch is not used for this illumination.
Our 68 does not have the "Wiper O'Ride" light. If the wiper electrical switch mounted at the bottom of the steering column that stops the wipers over the windshield to the wipers can be cleaned or changed should always be in the off position unless it is being used for wiper maintenance in stopping the wiper action.

[Clem Z.]

Re: 1968 Current Drain Problem

a quick check for a light stuck on in the glove box or a trunk is as soon as you open the door or trunk touch the bulb area and if it is warm it has been on before you opened it