1994 Chevrolet Suburban Electrical

Tiny
SDP0446
  • MEMBER
  • 1994 CHEVROLET SUBURBAN
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
There seems to be an electrical drain on my suburban. It was running fine, but suddenly started needed to be jumpstarted out of the blue. I've replaced the battery, alternator, and starter, and I've had all the tested numerous times just to be sure I didn't get a bad replacement. At the same time the battery started draining, I noticed that the tape deck was continuously cycling as if trying to eject something. I pulled the fuse for the radio, which cut power to the tape deck but did not fix the battery drain. Since the tape deck is obviously shot anyways, I cut and capped the wires for it, but once again it did not fix the battery issue. The previous owner of this suburban had a remote start and hornet alarm system installed on the vehicle. It always worked fine for me, but I can't rule that system out as a possibility and have no idea how to disconnect it to see if the battery stays charged without that connected. I should also mention that the previous owner managed somehow to bust all of the door panels inside this vehicle, resulting in the automatic door locks to not function. But again, this issue was sudden. One day everything was fine, the next there was a phantom drain on the battery. The only other issue that seemed top correspond was with the tape deck. Oh and I have checked all of the wires for the battery, alternator, and starter, and they are all fully and properly connected. Thanks!
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Friday, January 17th, 2014 AT 3:10 AM

3 Replies

Tiny
CARADIODOC
  • EXPERT
You don't have to cut the wires to the radio. Just unplug the connectors. There will be two power supply circuits for the radio, and either one of them can have a drain. Most commonly the display will fail to turn off when the ignition switch is off. That typically takes two days to drain the battery.

Did you have the charging system tested on the vehicle or did you remove the generator for testing? Does the "battery" light on the dash turn on, then go off once the engine is running? If so, to be sure we aren't chasing in the wrong direction, measure the battery voltage while the engine is running. It must be between 13.75 and 14.75 volts. If that is okay, you'll need a digital volt / ohm / amp meter to start testing for the current drain. You'll also need some clip leads, (jumper wires).
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Friday, January 17th, 2014 AT 3:39 AM
Tiny
SDP0446
  • MEMBER
The wires running to the tape deck and to the radio control panel may plug in somewhere up under the dash, but they do not unplug from the actual units. The alarm system has so many wires under the dash that there was no way to find where the radio wires were in there. It doesn't matter now, either way.

The alternator, battery, and starter I had tested individually while removed from the vehicle. I have not had any of them tested while still installed. It will be Tuesday before I can get back out there to try what you suggested, but I will update you after that. Thanks for your help!
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Friday, January 17th, 2014 AT 5:43 PM
Tiny
CARADIODOC
  • EXPERT
You must have an aftermarket replacement radio. If so, disregard my comment about the display failing to turn off. If you have an original system, GM used a lot of three-piece systems to prevent people from replacing them with something better. If you cut the wires on the control box with the switches and display, you still have the receiver box in the dash that could be causing the current drain.

Off-engine testing of the generator is not a good test of the unit. You can do the first part of the test with an inexpensive digital voltmeter. The second part requires a professional load tester to measure full-load maximum current output. That will require from five to eight horsepower to run the generator. In-store test benches rarely have motors larger than one horsepower. Also, they will run the generator at roughly idle speed which can show if there's some output, but not how much. All generators are very inefficient at slow speeds, so all on-car testers require engine speed to be increased to 2,000 rpm to get accurate results.

We also run into plenty of wiring problems that cause the charging system to be dead. Naturally, those won't show up with off-car testing. The other thing that doesn't show up is when the generator has one bad diode of the six. You will lose exactly two thirds of the generator's output. 30 amps from the common 90 amp generator is not enough to run the entire electrical system under all conditions. The battery will have to make up the difference until it runs down over hours or days.

As a side note, GM has had a huge problem with their generators since they redesigned them for the '87 model year. They develop large voltage spikes that can damage the internal diodes and voltage regulator. To reduce the number of repeat failures, replace the battery at the same time as you replace the generator, unless it is less than about two years old.

Holler when you have the amp meter and clip leads. To test for the current drain you'll need to use one clip lead to connect one meter lead to the battery's negative post, (you may need a bolt and nut to attach to the battery), another clip lead to attach the other meter probe to the cable, (you'll need a nut there too), and most importantly, a third clip lead to temporarily connect the two meter leads together.

Connecting to GM battery terminals and cables is a miserable and time-consuming job. For this low-current testing it is acceptable to clip a clip lead to the threads inside the battery's post, but contact on the cable is not made through the 5/16" bolt. Contact has to be made to the metal disc recessed in the end of the cable. That's where the nut comes in because there's nothing else to clip to.
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Saturday, January 18th, 2014 AT 1:05 AM

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