Technical Help: bad electrical component causing dead battery?

[GeigerUncounter]

I've acquired a 1977 124 Spider that hasn't seen much action in ~1 decade. I've had it ~1 week & the most important stuff works. I've done a number of small trips around town. Yesterday in the garage I wanted to catalog everything that needs repair by flipping all knobs/switches and marking what's not working. I found that the wipers don't work (but the wiper fluid pump does) and the cabin air/defrost fan doesn't come on, and one of the air levers is locked/frozen. I left the car for a couple of hours and when I returned I thought I could smell plastic burning. I hunted for the smell & found a small electronic component under the hood that seemed like it might be hot, but I wasn't sure. I left the car overnight with the hood up and when I returned I the smell was gone but the battery was dead!

I figured I must have left something on by mistake so I went through all knobs/controls using the owner's manual to make certain that everything off (it was). Then I jumped the car & drove it around for ~20 minutes. Left it in the garage ~1 hour being very careful that the doors were closed, no lights were on, etc. & checked on it to see if the burning smell returned (it hadn't). Left it overnight & in the morning it was dead again!

I don't think that there's anything wrong with the battery or alternator because it had run fine all week with multiple short trips around town. I think it's more likely that an electrical component is shorting somewhere & draining the battery. Perhaps turning knobs & flipping switches pushed an old brittle electrical part over the edge?

My question is: what is the best way to find the malfunctioning electrical component? I was thinking of the following:
- Jump the car & recharge battery by driving around town
- Park in the garage and disconnect all fuses
- Return every ~8 hours and check the battery, if it looks OK then replace a fuse
- Repeat the above step until the battery dies

Using that approach I can isolate the bad component to the circuit running through that fuse. It's a slow process though, is there a faster or more efficient way to do this? Any other ideas as to root cause? Any thoughts appreciated, thanks!

EDIT: typo fix

 

[bugsymike]

I've acquired a 1977 124 Spider that hasn't seen much action in ~1 decade. I've had it ~1 week & the most important stuff works. I've done a number of small trips around town. Yesterday in the garage I wanted to catalog everything that needs repair by flipping all knobs/switches and marking what's not working. I found that the wipers don't work (but the wiper fluid pump does) and the cabin air/defrost fan doesn't come on, and one of the air levers is locked/frozen. I left the car for a couple of hours and when I returned I thought I could smell plastic burning. I hunted for the smell & found a small electronic component under the hood that seemed like it might be hot, but I wasn't sure. I left the car overnight with the hood up and when I returned I the smell was gone but the battery was dead!

I figured I must have left something on by mistake so I went through all knobs/controls using the owner's manual to make certain that everything off (it was). Then I jumped the car & drove it around for ~20 minutes. Left it in the garage ~1 hour being very careful that the doors were closed, no lights were on, etc. & checked on it to see if the burning smell returned (it hadn't). Left it overnight & in the morning it was dead again!

I don't think that there's anything wrong with the battery or alternator because it had run fine all week with multiple short trips around town. I think it's more likely that an electrical component is shorting somewhere & draining the battery. Perhaps turning knobs & flipping switches pushed an old brittle electrical part over the edge?

My question is: what is the best way to find the malfunctioning electrical component? I was thinking of the following:
- Jump the car & recharge battery by driving around town
- Park in the garage and disconnect all fuses
- Return every ~8 hours and check the battery, if it looks OK then replace a fuse
- Repeat the above step until the battery dies

Using that approach I can isolate the bad component to the circuit running through that fuse. It's a slow process though, is there a faster or more efficient way to do this? Any other ideas as to root cause? Any thoughts appreciated, thanks!

EDIT: typo fix

If you have a decent amp meter in between battery lead and post, unless you have an accurate clamp on type , then turn on individual switches etc until you see a large drain on the battery.
Don't try and start the car , unless you have a good clamp on amp meter (600 amp plus) otherwise you will destroy the amp meter, what you are looking for may only be a .5 of an amp drain overnight.
Can be anything from a boot light , courtesy light, wiring wrongly connected to a switch, a headlamp wired wrongly, the wrong design of bulb in a socket (single instead of twin contact etc. even an alternator with a duff diode can drain a battery although still provide some charging to the system.
A quick test with everything switched off , is to disconnect and reconnect one terminal of the charged up battery and check for a slight spark.
This is harder on modern cars as alarms and ECUs don't shut off immediately.
Best to charge battery overnight with a good battery charger as if battery totally flat you would have to cover some distance to fully charge a battery.

 

[GeigerUncounter]

If you have a decent amp meter in between battery lead and post, unless you have an accurate clamp on type , then turn on individual switches etc until you see a large drain on the battery.
Don't try and start the car , unless you have a good clamp on amp meter (600 amp plus) otherwise you will destroy the amp meter, what you are looking for may only be a .5 of an amp drain overnight.
Can be anything from a boot light , courtesy light, wiring wrongly connected to a switch, a headlamp wired wrongly, the wrong design of bulb in a socket (single instead of twin contact etc. even an alternator with a duff diode can drain a battery although still provide some charging to the system.
A quick test with everything switched off , is to disconnect and reconnect one terminal of the charged up battery and check for a slight spark.
This is harder on modern cars as alarms and ECUs don't shut off immediately.
Best to charge battery overnight with a good battery charger as if battery totally flat you would have to cover some distance to fully charge a battery.

This is a great idea! I'll do this! And thanks also for the caution about attempting starting the car in this configuration!!

 

[s130]

Parasitic Battery Drain Testing. Nice video here.

 

[Pugglt Auld Jock]

This is a great idea! I'll do this! And thanks also for the caution about attempting starting the car in this configuration!!

As usual, great advice here from Mike. I remember having amps and volts explained to me by my college tutor back in the '60s as being like water in a pipe. Volts is when you hold back the flow of water and measure it's pressure - so things stay quite nice, tidy and clean - whereas Amps is like you removed the tap altogether and measure the water cascading out of the end of the pipe - makes a hell of a mess! So it's always worth remembering that measuring Voltage is a "safe" thing to do but measuring Amperage can be catastrophic if you don't know exactly what you're doing.

I prefer not to use an ammeter in series with a car battery because as it doesn't limit current flow like a voltmeter you can burn stuff out if you don't take great care - there's a lot of checking you can do using a voltmeter - but when I really have to I check for residual current draw with my 10 amp analogue meter and would never even think of operating the starter. Also make sure all systems are "off" before connecting - stuff like heated rear screens can draw heavy currents. If I connect it and find there's a substantial draw I then start removing fuses one at a time until the one i just removed causes the meter needle to drop. Then I know it's something in that circuit which is the problem. It's often something "silly" like a boot (trunk) light which has failed "on" so the light is still drawing current when the lid is closed.

Things are not so simple with more modern cars as they have systems which seem to draw current all the time but you're looking at resting current expectations of well under an amp after the car has been dormant for a wee while - probably less than 100 milliamps after maybe say 15 minutes so systems have time to go dormant. On my 10 amp analogue meter I usually say to myself that if the needle "kicks" I've probably got a problem worth investigating. I tend to stay away with multimeters as I've "blown up" more than I've had hot dinners doing this!

 

[Pugglt Auld Jock]

Parasitic Battery Drain Testing. Nice video here.

I was just watching this video and it's pretty good for the basics. However, I'd strongly advise against simply removing a battery terminal, as shown here, on a modern vehicle. Doing so will cut power to systems which need to stay permanently powered on and you may find that stuff like radio codes, automatic window up/down settings and a host of more important functions may be lost. In extreme cases this may not be rectifiable without an expensive visit to a main dealer and his diagnostic machine. It's one reason why I only use my 10 amp meter for testing. I clamp the meter's neg lead to the battery earth cable before disconnecting from the battery and then hold the meter's positive lead against the battery negative post as I slacken the negative lead and remove it. I then reposition the meter's positive lead, maintaining connection all the time, so it can be clamped to the battery negative post thus keeping electrical continuity at all times. - essentially it's repalcing the battery negative lead (battery negative post to earth) If I subsequently need to connect a multimeter to read milliamps, it's then easy to simply interpose it between the negative gauge lead and the battery earth lead and, because the "big" ammeter has done little more than "kick" I already know I'm not going to short the milliampere reading multimeter.

I have to say, Electronically I'm a dinosaur so I don't get involved in anything I'm not pretty sure about. Getting it wrong on modern vehicles using ammeters can end up very expensive!

 

[Pugglt Auld Jock]

By the way, while we're talking about using meters, You need to think carefully about how you may be intending to use an ohm meter. I used to use one for checking continuity and I was lucky enough to have a very nice analogue Avo minor gifted to me by a retired friend. Many years ago I acquired an old vertical receiver air compressor which was ideal for my workshop as it had a small footprint. The electric motor on it didn't work when I connected it up, just "hummed"" but didn't rotate, so I started "investigating" - not really knowing what I was doing as all my experience is with DC car stuff. Anyway, some of you guys will be ahead of this story already? A mains motor has capacitors to aid starting? and yes, Despite the motor being unplugged I wrecked the meter by using it on the ohms scale measuring a circuit that included the , still charged, capacitors. I'm still very angry with myself to this day, some 45/50 years later!

 

[bugsymike]

Easily done if distracted by something or someone.
I have used a simple multimeter for check steam cleaners aa wel as lots of vehicles over the years, however it takes me a long time tracing a fault on those and a lot of talking to myself.
When I feel like really chancing my arm I wire up my three phase 415volt motors etc. and check the voltage across the phases of my 10Hp Rotary phase convertor. I am the only one likely to use any of it and so far still here to tell the tale

 

[s130]

It goes without saying that all tools can be use correctly and incorrectly. Despite having a degree in electrical and electronic engineering, a career designing and testing both power electrical systems and electronics I made a simple and stupid mistake a few years ago.

A lamp outside my front door was not working. Was also dark with limited light from the hall light. I went to check the supply voltage not realising the meter was set to Amps. Big blinding SPLASH and a shower of molten cobber from the mains leads and the meter tips. Thankfully I was wearing glasses otherwise I could have seriously damage one or both eyes.

The splash was bigger than one might get somewhere else in the house as the light was only 12 inches away from the main consumer unit.

As with all these types of errors / accidents where you come out unscathed a second human feature occurs. "I hope nobody was watching out of their windows when I screwed up"! They would have seen a man standing in his porch messing with a light followed by flash and bang and the image of a brightly illuminated person looking rather jumpy and sheepish.

Next, do you tell the wife or just quietly retreat ......

 

[bugsymike]

It goes without saying that all tools can be use correctly and incorrectly. Despite having a degree in electrical and electronic engineering, a career designing and testing both power electrical systems and electronics I made a simple and stupid mistake a few years ago.

A lamp outside my front door was not working. Was also dark with limited light from the hall light. I went to check the supply voltage not realising the meter was set to Amps. Big blinding SPLASH and a shower of molten cobber from the mains leads and the meter tips. Thankfully I was wearing glasses otherwise I could have seriously damage one or both eyes.

The splash was bigger than one might get somewhere else in the house as the light was only 12 inches away from the main consumer unit.

As with all these types of errors / accidents where you come out unscathed a second human feature occurs. "I hope nobody was watching out of their windows when I screwed up"! They would have seen a man standing in his porch messing with a light followed by flash and bang and the image of a brightly illuminated person looking rather jumpy and sheepish.

Next, do you tell the wife or just quietly retreat ......

I once held the relay in manually on a old garage chain driven ramp motor as I was keen to get a job done, stupidly forgetting what I was doing bypassed the cut out when it reached the top thereby breaking the four threaded nuts on the pillars!
I was not very popular at the time.
It was called a Coronation Ramp so I am guessing the Queens Coronation around 1952? ish.
We had another similar at a previous garage which regularly broke it's chain drive due to mechanics (not me this time) leaving blocks of wood or bars etc. on the floor when it came down as this was well before "toe protection".
On another related point after a "incident" have you ever noticed a tang or taste in your mouth, I put down to an Adrenalin rush as opposed to the other type described as "brown trouser moments".

 

[Pugglt Auld Jock]

It goes without saying that all tools can be use correctly and incorrectly. Despite having a degree in electrical and electronic engineering, a career designing and testing both power electrical systems and electronics I made a simple and stupid mistake a few years ago.

A lamp outside my front door was not working. Was also dark with limited light from the hall light. I went to check the supply voltage not realising the meter was set to Amps. Big blinding SPLASH and a shower of molten cobber from the mains leads and the meter tips. Thankfully I was wearing glasses otherwise I could have seriously damage one or both eyes.

The splash was bigger than one might get somewhere else in the house as the light was only 12 inches away from the main consumer unit.

As with all these types of errors / accidents where you come out unscathed a second human feature occurs. "I hope nobody was watching out of their windows when I screwed up"! They would have seen a man standing in his porch messing with a light followed by flash and bang and the image of a brightly illuminated person looking rather jumpy and sheepish.

Next, do you tell the wife or just quietly retreat ......

Oh Lordy no, never admit to something like that. Mine has a memory like an elephant and still casts up things that happened years ago and are long forgotten by me.

 

[Pugglt Auld Jock]

I once held the relay in manually on a old garage chain driven ramp motor as I was keen to get a job done, stupidly forgetting what I was doing bypassed the cut out when it reached the top thereby breaking the four threaded nuts on the pillars!
I was not very popular at the time.
It was called a Coronation Ramp so I am guessing the Queens Coronation around 1952? ish.
We had another similar at a previous garage which regularly broke it's chain drive due to mechanics (not me this time) leaving blocks of wood or bars etc. on the floor when it came down as this was well before "toe protection".
On another related point after a "incident" have you ever noticed a tang or taste in your mouth, I put down to an Adrenalin rush as opposed to the other type described as "brown trouser moments".

I learned my lesson about mains electricity at a very young age and have never forgotten it. Towards the end of my time in school I was a classroom monitor and it was my responsibility to check the lights were all out after classes. On this occasion I was in a hurry so went down the row of doors reaching round the door frame whilst actually standing in the corridor to switch each light switch off - which was just inside the door on the wall. Unbeknownst to me the plastic fitting had been damaged and some of the plastic was missing so when I put my hand over the switch I was able to touch the bare metal parts inside the switch. The resulting shock I remember to this day. It was violent and seemed to make my whole arm jerk and the next thing I remember was finding myself sitting on the floor feeling very shaky indeed. It's given me a lifelong respect for mains electricity - I was a very lucky boy to get away with it.

 

[GeigerUncounter]

I'll give a quick update for anyone interested. Bugsymike's post and s130's video were extremely helpful. I followed that advice and measured 7 amps of parasitic current draw! 7 Amps at 12 Volts corresponds to >80 Watts, which is much larger than I expected! This must be quite a short!

Pulling fuses one & a time I was quickly able to isolate the short to a single circuit. The owner's manual says the offending fuse runs the "Windshield wiper, Heater fan motor, Windshield washer pump". I disconnected all electrical from windshield washer pump but the parasitic draw remained, so the washer pump is exonerated. I figure the bad component must be either:

(1) the windshield wiper motor
(2) the wiper switch on the steering column
(3) the heater fan motor
(4) the heater fan switch in the center console
(5) a random wire connecting to those components shorting to ground somewhere in a wiring harness

I think components #1-4 are most likely because I was futzing with them immediately before the problem appeared. I'll investigate those more closely when I have time this weekend. Thanks again for the help everyone!!

 

[Pugglt Auld Jock]

I'll give a quick update for anyone interested. Bugsymike's post and s130's video were extremely helpful. I followed that advice and measured 7 amps of parasitic current draw! 7 Amps at 12 Volts corresponds to >80 Watts, which is much larger than I expected! This must be quite a short!

Pulling fuses one & a time I was quickly able to isolate the short to a single circuit. The owner's manual says the offending fuse runs the "Windshield wiper, Heater fan motor, Windshield washer pump". I disconnected all electrical from windshield washer pump but the parasitic draw remained, so the washer pump is exonerated. I figure the bad component must be either:

(1) the windshield wiper motor
(2) the wiper switch on the steering column
(3) the heater fan motor
(4) the heater fan switch in the center console
(5) a random wire connecting to those components shorting to ground somewhere in a wiring harness

I think components #1-4 are most likely because I was futzing with them immediately before the problem appeared. I'll investigate those more closely when I have time this weekend. Thanks again for the help everyone!!

Just a random guess, self parking circuit in the wiper motor?

 

[bugsymike]

Does it still drain with key out, if so I suspect someone has wired in something non factory.
Check any aftermarket radio wiring etc.
Also see if disconnecting all alternator wires affects it, as I mentioned before a faulty diode in alternator can cause battery drain.
Safely insulate wires against shorting when doing this test.

 

[GeigerUncounter]

Does it still drain with key out, if so I suspect someone has wired in something non factory.
Check any aftermarket radio wiring etc.

This is a very interesting comment. Yes, the parasitic current persists even with the key out. An aftermarket radio/cassette player was installed in 1992, so that counts as non-factory wiring. However, what catches my attention more is that a bunch of aftermarket emissions compliance gear was installed in the mid-90's and then ripped out shortly before I acquired the vehicle last month.

There are strict emissions rules where I live, but recently exceptions were carved out for antique cars. This 1977 124 is old enough to qualify for the exemption, so the prior owner removed the gear immediately before I acquired it. It's only had ~250 miles on it since the gear was removed, so it's a recent change. When I look around the engine bay I've counted at least 6 wires mysteriously terminating into nothing. Two of them exit the carburetor before terminating, so I've assumed that these mysterious wires must be remnants of the removed emissions gear?

Perhaps the emissions gear was patched into this fuse's circuit, and was removed sloppily producing this short? This certainly gives me a new angle & a lot to think about...

Also see if disconnecting all alternator wires affects it, as I mentioned before a faulty diode in alternator can cause battery drain.

This should be an easy test. Thanks for the suggestion, I'll try this as well!