97 855 GLT - (more) electrical gremlins

Post by **vjaneczko** » 03 Jun 2014, 16:53

I'm STILL in the process of running down an electrical gremlin and over the last year or two I’ve replaced the alternator & serp belt, replaced the battery, replaced a few of the ground cables, but I still deal with a battery drain, poor idling & charging, etc. I don’t believe it’s the B+ cable from the issues I’m experiencing. I figure it’s gotta be the positive connection from the alternator to the battery, so I purchased a new cable – only later did I discover I need two cables; one from the battery to starter and from the starter to alternator, but I'm curious about a few things.

First off, the battery was dead so I left it in the car and charged it overnight with a Black & Decker 10 amp charger (https://www.amazon.com/Black-Decker-BCS1 ... 0024GJ4IM/ if you’re curious). The next afternoon, it was fully charged. I cranked the engine to make sure it started properly and it did without hesitation. I shut it off and went to remove the battery. Oddly, the positive battery terminal was very warm and the negative side wasn’t. Is this normal from overnight charging? I’d think if it was, both sides would be warm.

So just to see if I could stumble upon anything else, I hooked-up my ohmmeter to various parts under the hood and I'm getting some odd readings. I was getting no resistance when connecting along the various cables, such as positive battery connector to positive alternator post. That told me that I didn’t need a new cable, but still had no clue what could be causing the problem. Then in frustration/silliness, I connected the positive & negative battery connectors and found resistance! Seems really weird. So I started poking around some more and decided to note some of the readings.

- From the top of the engine to the positive battery connecter, I read 2.116 M ohms.

- From the positive connector on the alternator to the negative battery connector is 14.16 M ohms.

That seems bad, in my mind. I shouldn’t have resistance between those parts, should I? That tells me that there’s a problem with one of the bazillion wires somewhere, right?

Post by **abscate** » 03 Jun 2014, 19:41

You can only measure resistance of isolated components and wires, so your connected resistance measurements don't tell much. You can also fry your meter if you aren't careful.

Post by **vjaneczko** » 03 Jun 2014, 20:59

I pulled the battery before I started probing and was only checking resistance so I wasn't too worried about the multimeter. I did check a few other things, such as the cable from the alternator to the start, and the starter to the battery but got 0 ohms which I expected so I didn't bother to note them.

1998v70xcbill · Post by **1998v70xcbill** » 03 Jun 2014, 21:49

the Meg ohms readings you got are fine. That's a very high resistance for 12 volts.
The warm battery cable should not be from the over night charging. Did you connect the charger cables to the battery posts? If no current should go though the cars cables. The warm pos+ cable was possibly from starting the car (high current). Maybe the Pos+ cable is getting old.
To drain battery you should have a much lower resistance between plus and ground (like 100's of ohms or 1000's ohms)
Maybe someone could measure A good car and post. I will try to do this

Post by **vjaneczko** » 14 Jun 2014, 16:31

so I pulled things apart and I'm getting 1800 ohms between the negative post cable and the b + cable. I pulled all the fuses one by one and nothing changed so it must be something coming off the b+ cable that is not fused - but what could that be? I've already ruled out the radiator fan and the sas pump.

Post by **Ozark Lee** » 14 Jun 2014, 17:18

Measuring resistance between the positive B+ cable and negative terminal is pretty useless. It doesn't tell you anything. A resistance measurement between the positive terminal and the B+ cable at the fuse box can be helpful if you suspect a bad B+ cable.

What are the underlying problems?

...Lee

Post by **vjaneczko** » 14 Jun 2014, 18:25

Battery won't keep a charge, headlights dim when you're not accelerating, low idle at a stop light & sometimes dies.

I'm curious why you say measuring between the B+ cable and negative terminal is useless. Except for open doors which turn on the overhead lights, shouldn't resistance be zero?

Post by **Ozark Lee** » 14 Jun 2014, 20:07

In a perfect world the resistance would be infinite. There are enough items in the circuit though that there will be some measurable resistance if you disconnect the battery and measure between the cables. Measuring resistance with an applied voltage just doesn't work. With an old school analog meter it will actually blow the meter or at least blow the fuse.

It sounds like you just have a bad battery, have you had it load tested?

...Lee

Post by **vjaneczko** » 15 Jun 2014, 07:55

Now you've got me thinking about the battery - could it be older than I remember, or just a dud?! I've not had it tested so maybe that's something I can pull off today.

Post by **vjaneczko** » 15 Jun 2014, 10:51

And now that I've had my morning (pot of) coffee, another thought enters my mind about the battery. Maybe I need more caffeine but once the car is started, shouldn't the alternator provide all the juice needed for the car? I thought the battery was only to start the car, with the alternator providing all the necessary electricity during driving but your question makes me question that belief.