dfinnegan

I am experiencing a battery drain problem which is killing the battery over a period of days of inactivity (3-5 days).

I have verified a bad interior light switch at the driver's door.

It has been somewhat intermittent in the past and has not worked at all lately. Upon inspection (removal of the switch) the interior light came on and would not go out regardless of switch manipulation (installed, removed, grounded, opened, closed; no change, light on).

I pulled fuse #11 (lights off) and measured a 37ma draw. Excellent.

Or so I thought. Several days sitting, another dead battery.
I've recharged (trickle charger) and driven the car a few times locally.

I've run some additional checks and have found battery voltages of

• 12.9 V prior to start with meter across battery terminals
• 13.65 V at idle (by meter at batt terminals) and 13.2 V (by Hammer)
• 13.4 +/- while driving and measured by Hammer; I'd like to call this 13.85 V "real" given the idle diffs of the hammer and meter; I can't measure the voltage and rev the engine at the same time while alone

It seems like my alternator/voltage regulator is working fine.

I then looked at draws at the battery (with fuse #11 still removed) and I now measure a 114 ma constant draw. Strange. A couple of weeks ago it was just 37 ma with fuse #11 pulled. No changes made since then.

I then pulled each fuse and relay, in turn, and noted a couple of 1 ma drops, a 14 ma drop pulling fuse #12 (diag, emerg flash, r wiper) and a 5 ma drop pulling fuse #38 (radio boost). Not very interesting.

Then I replaced fuse #11 and the boot light popped on and produced a 2+ A draw (2000+ ma). Okay.

Now the strange bit. I hit the boot switch button, the light goes off and the draw drops to 37 ma. Fuse #11 in or out, still 37 ma draw.

It seems that the interior light and clock circuit is the likely culprit.

However, I'm confused about how I could measure a 114 ma draw with fuse #11 pulled. Would that not isolate the interior light and clock circuit, eliminating it from consideration?

How does the 114 ma draw disappear after re-installing fuse #11 and lighting the boot lamp?

I have received two new door switches and will replace them, but fear that I've not figured out the root cause.

Any insights?

darth

Dear Dfinnegan

I'm not sure if you know this, or if it will help in diagnosing you problem, but, if I remember correctly the engine compartment light is tied in with the trunk light. The engine compartment light will come ON (i.e. viewable through the engine grill when engine lid is closed) when the trunk is opened.

"I can't measure the voltage and rev the engine at the same time while alone" If your meter has long enough leads that can clip onto the battery, so that you can view the meter (i.e. while it sits atop the drivers side front fender) from the drivers seat while you rev the engine, you should be able to see if it is charging properly.

Hope this helps
Bill

springer3

When things make no sense, there is usually a different explanation. My guess is you have an intermittent problem in a circuit different from the one you are troubleshooting. Perhaps what you did triggered something that is bi-stable, with one state being normal, and one state being "current draw".

A possible clue is the magnitude of the draw. The CCU and the spoiler module drive relays that pull about 100 mA even when the main power switch is off.

Good luck, and remember: patience, patience, patience.

Second Childhood

I just went through this issue with my 1993 RSA. I had about a 90ma draw regardless of what fuses I pulled. Both of my interior lights were on, so I switched them off. The trunk compartment light was unplugged. What I discovered is that if I left the trunk lid open and did not trip the micro-switch in the trunk latch, there was evidently a battery draw going on. Once I tripped the trunk latch, the draw went down to 18ma. Another thing that caught me was that the interior lights are on a 30 second delay after you close the trunk and/or doors. I was not waiting for those to go out before assuming I had a problem with the lights. I had already replaced both door switches.
Don't know if that helps.

dfinnegan

It always helps to have more data!

Thanks for the inputs so far. I'll continue chipping away at it and post back as I learn new bits of information.

Cheers

dfinnegan

I have some more data points for my electrical issue.

First, I've not been able to reproduce the high draw issue.
I am now seeing 26 mA draw.

As for the door light switch circuit, that appears to be fine, as well. I've "discovered" the 30 sec delay in the door switch circuit. So the lights do go off and on as expected.

I managed to get a view of my electric meter by positioning it on the fender as darth suggested.

The voltage on the battery is dropping and des not rise with rising rpm. Instead, it falls.

Does this suggest an issue with the alternator/regulator?

Indycam

What kind of battery do you have and how old is it ?

darth

Dear Dfinnegan

I'm assuming the battery connections are clean and there is no concern of a bad connection.
After the 30 minute drive what was the voltage right after you turned the engine off? It should be around 12.6Vdc. While starting the engine what is the lowest voltage observed? It shouldn't go below 9.9Vdc. The fact that it is 13.8Vdc at idle is OK but the voltage shouldn't decrease as engine rpm is increased. The battery is suspect, I think a load test is in order.

Bill

dfinnegan

The battery is an Interstate and it is 5 yrs old.

After further diagnostics and researching today the final entry in my notes was "battery suspect". Interestingly enough.

I plan on bringing the battery in for a load test tomorrow.

In the mean time I've been searching for local sources for an Optima Red Top Group 35. I believe this is the correct model for our cars.

Is that correct?

As for futher diagnostics, I failed to note the voltage during cranking, but did see the voltage drop into the 11V range upon turning the ignition on to position 2 (just short of running the starter motor).

I noted 12.3V and 25 mA draw at the start of this session; after having left the battery connected for 24 hrs.
It ran 13.8 down to 13.6 while idling and rev'ing to 3k rpm (cold engine) with various lights, high beams, radio and fan. After 5-10 mins the level was 13.6V.
During a 30 min run the Hammer indicated 13.4-13.6 with occasional 13.7-13.8 peaks. Remember that the Hammer, on my car, reads ~0.4V lower than my meter on the battery terminals.

I was unable to check the voltage at the termination of the run as I arrived home late and had to run out immediately.

I agree that a load test is in order and will try and get that done tomorrow.

Thanks, again, for the insights and input.

I'll post additional information as it becomes available.

Cheers,
Dave

chris walrod

Typical battery life is 5 years. With that, I would replace the battery. Also, have a look at the batt ground strap condition, and its connection to the chassis.

Causes of drains like this have been attributed to bad radio's, CCU's and like you've already mentioned interior dome lights and their associated switch gear.

Good luck with this -- drains can certainly be frustrating!!

wit007

Check the small CCU fan.

dfinnegan

I've purchased and installed a new battery.

I'll continue monitoring and post back if I learn anything of significance.

For now I have:

12.6 V out of the wrapper
12.59 V after first 20 min drive; Hammer showed 12.4-12.7 throughout (+0.4 to get battery terminal voltage).

It sat for 24 hrs and I then ran a few errands, got an inspection, gas, tootled around town and went for a 20 min drive.
12.64 V upon return.

After 5 mos without the car, I'm back looking for excuses to go for a drive; as if I need one!

Indycam

Test test test , keep on testing mile after mile .
Data acquisition by the tank full .
Make the sacrifice for science .

darth

Dear Dfinnegan

What type of battery did you purchase and what are the specs? Did you have the old battery load tested? If so, what were the results? Does the voltage still decrease as engine rpm increases?

Bill

Indycam

https://rennlist.com/forums/964-foru...st-option.html
"I ended up with an Interstate MTP-91 Mega-Tron Plus, 85 Months, 700 CCA, $124 plus tx.

Thanks, all, for the input!

Cheers
__________________
1991 C4 Coupe, Polar Silver
The hours a Porsche spends parked. You don't get those back."