Delco Truck Radio

[Ed446]

At work we have a 95 Chevy truck with a factory Delco AM FM radio. The clock display stays on all time. If the truck is not driven for a few days, the clock will drain the battery.
Ed

[jimandy]

Are you sure it's the clock display? Several things usually run all the time in most vehicles but draw very little current, and the battery should hold them up for weeks. Have you tried disconnecting the radio to see if it's the problem? (EZ way to do that - pull the fuse).

[Sterling Martin]

Hi Ed,
I used to work on cars and trucks for a living, and I seriously doubt that the draining problem is your display. If you want to check, a very easy way to do that is to disconnect your battery cable and insert an ammeter between the battery and the battery cable. Start unplugging fuses untill you find the one that drops the current to almost zero. Be advised that when you disconnect the cable and reconnect it, there is a little bit of current moving normally to reset the computer, etc. Leave it settle down, and then do your testing. Good luck!

[jimandy]

Actually, using Sterling's suggestion, you might pull fuses one at a time and measure with the ammeter across their open terminals to isolate the guilty circuit (the one drawing the most current). But I'm not sure what else that is normally fused, other than the radio's clock, would be drawing current. From my limited knowledge of auto batteries (lead acid) you could have a bad cell in the battery. What say you Sterling?

[gerty]

I had a '89 Chevy pickup that had the same clock problem. The 'RCL' button was stuck, it allows you to check time with ignition off. But like the other posters I don't think that'll run down your battery, didn't mine anyways.A common problem is the tilt switch for the underhood light getting out of whack, usually loose screws. If you have one just raise the hood and see if the bulb is hot. Make sure you're parked level, or in the same position as usual when you check it.Another problem is the brake light switch sticking.
Then again you might just have a weak battery

[Chris Smith]

Don’t forget to wash down your battery top. <p>Acid vapors deposits crystals over the top of the battery and form a path to cause a short. <p>All of the GM classes I have attended show this as the main cause [but not exclusive] of battery drain. <p>All of the above advise not withstanding. <p>Pull fuses, and check all possibilities.<p> Do a battery positive lead current draw, at the battery with a ammeter and find out just how much is being withdrawn. <p>Electrical and electronics faults was my speciality at GM. <p>Boil some hot water, wet the battery down, pour baking soda all over the battery top, wet, repeat, and wash off with plenty of boiling water, followed by the cold running water. <p>Then clean the terminals the same way, including Filing and or brushing.

[terri]

Using similar diagnostic techniques I found an intermittent current draw from the battery, cycling about every twenty-thirty seconds or so. Tracked it down to the cigarette lighter, which had been pushed in just enough to make contact, warm, slightly and disconnect itself again and then repeat the cycle when it cooled.

[gerty]

Terri, I'll bet that was a tough one to find..

[Ed446]

The battery is not over 6 months old, the top is clean. The under hood lamp is cold, also don't light with the hood open. Pressed the recall button several times, don't seem to be stuck.
Probably will try pulling the radio fuse.
Thanks
Ed

[Sterling Martin]

Yeah, jimandy, your suggeston of connecting the ammeter across the pulled fuse jack is a good idea! I have never seen that done, but it has got to work. I'm positive that just a few minutes of working with it would find the circuit that is still drawing current after the ignition is off. I also think that if I remember right, there might be a small steady state current ( less than 1/2 amp. )

[philba]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Sterling Martin:
Yeah, jimandy, your suggeston of connecting the ammeter across the pulled fuse jack is a good idea! I have never seen that done, but it has got to work. I'm positive that just a few minutes of working with it would find the circuit that is still drawing current after the ignition is off. I also think that if I remember right, there might be a small steady state current ( less than 1/2 amp. )<hr></blockquote><p>Take a burned out fuse and solder on a wire to each contact (but not so it makes it hard to insert the fuse). Hook the other end of the wires to you meter probes. Now you can just insert the special "fuse" rather than fumbling with probes while trying to see the meter.

[terri]

Oh, another one was a neighbor's car where the glovebox light switch button was worn down enough to keep the glovebox light on. Hard to spot the light being on with the glovebox closed.<p>I dunno, somehow it seems to me these little "trickle-drains" are far more significant in draining a battery than would be indicated by just dividing the Amp-Hour rating by the current draw of the appliance.<p>One car I owned was so highly engineered that nothing would work if the battery dropped below 10 V. It was the first year that they used computer control, and I guess their Teutonic minds thought, "Vat? You cannot haff die Komputer run on less zan tsehn folts! Ve cannot allow ziss to hoppen! Nicht wahr? Ja wohl!"<p>So it shut down at ten volts and nothing would work! And I mean Zero-Point-Zero nothing!<p>
Boy, do I have a story about that car's electrical system! Talk about uber-engineered!<p>[ January 29, 2005: Message edited by: terri ]</p>

[mick]

I would not use an ammeter to check an open fuse. When the fuse is out and you use an ammeter like that, the circuit is complete adn current flows. I work in an duel GM & Chrysler dealership. I am a Chrysler Master Technician and our training is now checking voltage drop accross the fuses to find the drain. You have to very small voltage signals.

[Chris Smith]

But mick, current is not supposed to flow, thus if it is, its most likely the cause. <p>Yes I too worked for GM, and thats exactly how we found current flow, that was supposed to be current off, when the car was at rest.
Tiny as in LED displays was ok, larger was not.<p>A voltage leak around a fuse will only indicate a resistance in the fuse, one that should not be there.

[terri]

Gerty: Yes, it was a tough one to locate. But process of elimination plus a schematic plus lotsacusin did the trick. As a matter of fact, the cigarette lighter was the very the last thing I checked.... (har-har-yuk-yuk.)<p>Chris, fuses have a small but significant resistance which will translate into a readable voltage when they are carrying their load. After all, if they had no resistance, they'd never blow, right?* <p>*P = I squared R, if R = 0, then power = 0. No power, no heat, no melt, no blow. I know you must know this Chris, so I wonder if you meant to say something else? (--I spelled out the power formula for other persons who might not realize that a zero resistance fuse will never blow.)