Help in testing circuit in a 1986 3.2

[GeorgeW]

Hi everyone.

I have missed reading this forum and have not really done so for about 3 years, but am now committed to fixing as many of the bugs and quirks in my 86 which I bought five and a half years ago. It has been and still is a great car and I love the feeling when driving it. Soon, I will have access to a shed, a quasi garage of sorts, and will be able to start projects requiring more time.

One of the bugs is that my battery is undercharged in the winter and I think I have identified the 'total interior lights' circuit as the problem. When its fuse is removed the current at the battery drops from 780 milliamps to 70. Bentley says anything over 400 is a potential problem. Sooo, what now?

It isn't clear which components are included in the 'total interior lights' circuit. Bentley lists several in its fuse location section and has a 2 page wiring diagram for the Instrument Panel ( assuming interior lights = instrument panel ) which shows things I don't think are in the car such as brake pad wear lights which seems to be part of a combination indicator lamp etc.

The circuit does include a clock which has never worked and also an after market radio/sound system which when off still has its LED display lit up.

I am hoping someone has been down this road and will share his or her experience. I can follow cook book like instructions and just bought a great Sears digital multi-tester ($20) which I love.

Would appreciate any thoughts comments. Thanks for reading the above.

[ChkbookMechanic]

To find which item/s that are causing a drain on the battery you'll probably have to go item by item unplugging / plugging them back in to see which one is causing it. However, you can speed up the process if you can find the wire that starts a circuit where the components are in series and just unplug it and test to see if the drain is caused by that particular circuit.

For the clock you can just pull it out then unhook and wrap up the 12V wire going into the clock then push the clock and 12V wire back into the dash. That way the clock won't be getting 12V since it isn't working anyway.

[911pcars]

That's good advice. I would begin with a copy of the wiring diagram. Photo-enlarge the circuits connected to the fuse circuit in question. Then take a colored pencil or marker and trace the current path to each of the loads in the circuit. This helps identify the wire color codes and the specific loads to inspect.

Begin by identifying, then disconnecting a suspected branch circuit in turn from the main circuit - one at a time. Separate the harness connector if one is available. Sometimes worn insulation allows a partial short circuit, not enough to blow the fuse, but enough to draw current. Wiggle the harness while observing the ammeter display.

Once you have identified the malfunctioning path or branch circuit from the "total interior lamps circuit, you can zero in on the actual load itself (bulb fixture) or path (source wire to load). Remove the bulb fixture from the vehicle and bench test using the continuity tester section of the meter.

Hope this helps,
Sherwood

[darrin]

George -- does your interior dome light still work? (i.e. do your interior lights go on when you open either your driver's side and passenger side door). My driver's side pin switch failed causing my dome light to no longer work. Subsequently, I too developed a battery drain problem which I eventually traced to the faulty door switch. Turns out that my electric window motor circuit was the culprit. The electric window circuit stays "armed" after the ignition's turned off to allow one to finish raising the window but is supposed to become disabled when one opens the door. Thus, since my switch had failed (it was really just dirty), the window motor circuit remained "armed" even after opening my door (the window would still go up and down with the door open) and drained my battery.

Since this is easy to check and a not-too-obvious cause of your problem, I thought I'd mention it.

[GeorgeW]

Thanks guys! Great tips on how to proceed and what to check.

I went through all the old documents which came with the car and the PO installed an audio amplifier under the passenger seat. My first check will be see how it is connected to power source(s).

Also, the alternator charging light in the tachometer never comes on. Strange I hadn't noticed it before. I hope it is a bad bulb and not indicative of an alternator/regulator problem.

[ChkbookMechanic]

Audio installs are some of the messiest things to diagnose in my opinion. The people installing audio equipment normally do a terrible job and take shortcuts anywhere possible. Splicing wires, leaving things dangling and in general doing a terrible clean-up and install job.

If your car is starting I wouldn't worry about the alt. charging light.. it is probably just a bad bulb. (I could be wrong on this)

[T77911S]

Originally Posted by ChkbookMechanic

Audio installs are some of the messiest things to diagnose in my opinion. The people installing audio equipment normally do a terrible job and take shortcuts anywhere possible. Splicing wires, leaving things dangling and in general doing a terrible clean-up and install job.

If your car is starting I wouldn't worry about the alt. charging light.. it is probably just a bad bulb. (I could be wrong on this)

as a former auto electric guy, some good points above. car alarms were my nightmare. when you start hacking up the wires for starting or running, your asking for trouble. nice tip about the door switch.

just to be safe, go have your battery load tested.

[rick-l]

+1 for the power window relay and the door switch.

How does the alternator work without the current through the bulb? I've heard they can start with residual magnetism at higher rpms but for how long?

[GeorgeW]

Have not had a chance to check anything yet. Will get to it this weekend.

Darrin - when opening the driver door the interior lights are not reliable. You may be on to something. Also, the passenger side power window switch does not function for the down cycle. The window has to be lowered at the driver side control. I remember the PO saying several years ago that he had replaced the passenger side control switch. Not sure why it was done.

Question: if the window power circuit were to stay armed due to a faulty door pin switch, when the power window circuit's fuse is removed shouldn't the amperage measured at the battery be lowered? When I removed that fuse it made no difference to the high amperage, 0.78 amps. Not sure if i am following all the information correctly

[RoninLB]

The alternator idiot light should should be on with the key in the "on" position and engine not running.

The idiot light is part of the charging circuit. Bad bulb = no charging.