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roadsidejerry, auto mechanic
Category: Chevy
Satisfied Customers: 2948
Experience:  Auto Mechanic 39 years, 30 with NYPD Fleet Service Division
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Chevrolet Silverado 1500 I have a 1990 Chevrolet Silverado

Customer Question

I have a 1990 Chevrolet Silverado truck with 5.7 L engine. Last year, I did some extensive work on my steering column due to a loose tilt mechanism. After tightening the four bolts, I also replaced the turn signal switch, wind sheild wiper switch, ignition key cylinder, the brake light switch and the ignition switch. Everything worked great until recently when the turn signals stopped working. I reached down and squeezed the multi-wire connector/harness together (located near the bottom of the column) and the turn signals began working again. Last week while driving during the evening (with head lights on), the turn signals failed again, but this time the tail lights and break lights also failed.
The next day, I pulled the same multi-wire connector apart and reconnected it. With the ignition turned to "On", and head lights off, the break lights and turn signals work, but tail lights do not. If I turn the parking light switch on, the brake lights, turn signals and tail lights will not light up. The bulb filaments for the tail lights look fine. What might the problem be?
Submitted: 6 years ago.
Category: Chevy
Expert:  roadsidejerry replied 6 years ago.

Hi, most likely the circuit boards that the lamp sockets are mounted on are defective, losing ground. Make sure you have power to the lamps when turn on all the lights, and have a good ground to the circuit board, if so the circuit boards need to be replaced. Below is information on what the circuit board looks like nd where you can purchase them at a good price online. They fail often.


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Car and Truck Parts > Lighting & Lamps > Tail Lights 88-99 CHEVY PICK UP Tail Light Circuit Board NEW PAIR
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DESCRIPTIONBrand New Taillight Tail Light Lamp CONNECTOR PLATE ( WHERE THE BULBS PLUG INTO) for the following years and models:

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Affordable Replacement Auto body Parts

All our parts are NEW replacement parts for your vehicle manufactured in the aftermarket to be the exact replacement for your OEM part. Many times, our parts are manufactured to correct the defect that is forcing you to replace the original defective part now! All our parts are NEW, STILL IN THE BOX and ready to be installed without hassle or prep time. All our parts come with a complete one year warranty against manufacture defects so that you can be confident that your part will work for your project the first time! You can count on quality parts from NATIONAL AUTO PART!

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Expert:  roadsidejerry replied 6 years ago.

Here is a better picture of the circuit boards, the ones in my answer may be hard to find and open.


Customer: replied 6 years ago.
I have replaced both circuit boards as you suggested as a possible cause of my problem and the same problem persists; when I turn on the headlight/parking switch, my turn signals,tail lights and brake lights do not function (headlights do function correctly); when I turn the headlight/parking switch off, the turn signals and brake light do function correctly. All ground connections are OK and I traced the wires in the circuit that operate the tail, brake, and turn signals from the fuse block to both bulb circuit boards and have found no obvious worn off wire insulation or breaks in the wiring. I also put my ammeter between the positive post of the battery and the positive battery cable and got zero. however. when I put the volt meter between the negative post of the battery and the negative battery cable or the vehicle's frame, I get nearly 12 volts. Is that normal and do you have any other ideas? Thanks!
Expert:  roadsidejerry replied 6 years ago.

If you put an hook your ammeter is series from the battery terminal and cable, you should get a reading when you turn the lights on. Be careful since most ammeter only handle 10 amps, or you will blow a fuse in the meter. The reading you are getting with the voltmeter indicates you have no ground at the trucks frame. The reading SHOULD be ZERO. Just make up a jumper wire and connect one end from the battery negative post and the other end to a clean rust free area on the frame, this should get the lights to work.This info should explain the testing procedures.

Voltage Loss or Voltage Drop, That Is The Question?


We hear the terms "Voltage Loss" and "Voltage Drop" test frequently in the Automotive industry. But most refer to it as what's is really a Voltage "Drop" test. This is incorrect, these are two separate test with two separate purposes - however, many-times the same failure result can be determined with both test. So what is the difference between the two test, and why do we perform them?

Well, it's actually what it states:

A Voltage Loss test is testing for a voltage "loss" across one or more connections or components. This test is performed on "one" side of the circuit at a time - meaning to test the Positive side of the circuit, and / or then test the negative side of the circuit.

A Voltage Drop test is to test for a voltage "drop" across one or more connections and components. This test is performed across both sides of the circuit and requires a component - meaning to test from the positive side of the circuit to the negative side of the circuit. This requires some sort of resistance through a load component like a light bulb or resistor, etc...

. This test is typically not performed across a component - although you can in some cases. It is typically used to test circuit hard wire connections - like a starter cable, or for a lose ground with lights flickering or dim on one side. A "General" rule is 0.5 volt allowance across each connection. If you are testing across several connections, it would be 0.5 Volts "per connection." Three connections would be 0.5 Volts X (3) Connections = 1.5 Volts loss allowance. Now this is a general rule, realistically it would be typically in the 0.35 to 0.37 volt range depending on wire length, gauge, number of connections, quality of connection, number of components and the resistance or voltage loss value of each component (any resistance equates to a volt loss value).

Edited by roadsidejerry on 1/24/2011 at 5:22 PM EST
Customer: replied 6 years ago.
When I connected the ammeter between the positive battery post and the positive battery cable, I made sure everything was turned off, in an effort to see if I had a current draw from maybe a short in one of the circuits, but got no reading, therefore i assumed no shorted circuits. When I put the voltmeter between the negative battery post and the negative battery cable, I got nearly 12 volts. When I put the voltmeter between the negative battery post and the vehicle's frame (I had to scrape the voltmeter lead against the sheetmetal before I was able to get a reading) I got nearly 12 volts. I did not try the lights at that point. I assumed that there should be no voltage draw during these tests so I pulled each fuse while viewing the voltmeter, but that made no difference in the voltage reading that I was getting.
Expert:  roadsidejerry replied 6 years ago.
To do the voltage drop test at either the frame or body, leave the battery cable connected to the battery, then with the lights on, connect one end of your voltmeter to the battery and the other end to the frame and body panels, you should have less tan a half a volt. You can make up a long test lead and check for the ground at the tail lamp also. I appears you have a poor ground that cant carry the load of all the lights at the same time. If when you connect the meter from the neg battery terminal and the frame and you do get a reading, try using a jumper cable from the battery neg to the frame,it should cause your meter to drop to zero, this will prove that you do have a problem on the ground circuit. You can then make a permanent connection to alleviate the problem.
Expert:  roadsidejerry replied 6 years ago.
Hi, If this testing procedure is confusing you, a simple test you can make would be using a jumper lead. Get a 20 ft length of 16 gauge wire with an alligator clip on each end,connect one side to the battery negative post then with the lights on, connect the other end to various metal parts of the truck, the frame .radiator support,cowl,rear body panels, be sure to connect to a clean paint and rust free area,when the lights work, you may see an electrical arc when you make the connection,you will have found the area with the poor ground. You can then make up a permanent wire to cure the problem.
Customer: replied 6 years ago.
I disconnected and cleaned everything associated with the grounds at fender next to the battery and the ground at the rear of the frame to the tail lights and still no success. I have been told that one reason for my problem is that I could have a bad IAC valve on the throttle body, thereby causing insufficient idle when my headlights are turned on. I assume the reduced idle plus the headlights being on would be not able to keep up with the demand from the other lights, such as in my case, the brake lights, tail lights and turn signals, which by the way do function when the headlights are turned on, just very slowly.
Expert:  roadsidejerry replied 6 years ago.
Hi, the turn signal.flasher operation could possibly be caused by a low voltage condition, but this would not affect the brake or tail lights . If you suspect low voltage is you problem, due to a defective IAC, raising the idle by pressing on the accelerator would confirm this. If you believe your charging system is the problem, have the voltage checked , as long as you have at least 12.6 volts with the lights on and engine idling, the lights should work fine. You really need to do the voltage drop testing as I described. Check for voltage drop, right at the tail lamp assembly, or run a ground wire from the battery negative post to the ground wire at the lamp. I have seen this problem many times confuse many mechanics.I am trying to help you as best I can without being there i person.
Customer: replied 6 years ago.
I finally found the problem. The ground wire that I initiallly thought was the ground wire for the tail lights, turned out to be the ground wire for a tailer plug. I recently had the bed of the truck moved back to gain access to the fuel pump that I had to replace. Before removing the bed, I disconnected several ground wires at the rear to stay clear of the moved bed. This last weekend I reached up on top of the rear of the frame only to find the tail light ground wire that I had pushed on top of the frame, where it apparently made enough contact with the frame, to make ground, until it finally swung loose, giving me no or insufficient ground. After connecting that ground wire, all lights are now working, however, when I put the volt meter between the negative post of the battery and the negative battery cable I still get 11.50 volts, while the battery voltage reads 12.50 volts. I also again, put a ammeter between the positive battery post and the positve battery cable and got zero current draw. Do I still have a grounding problem, as I believe you stated that I should be getting no voltage on the negative side?
Expert:  roadsidejerry replied 6 years ago.

Hi, glad to hear you found the problem with the lights. If you are not getting a reading on the ammeter between the battery post and cable then you don't have a drain. As for the voltage drop testing, this is done with the cable connected to the battery post,you just touch one test lead of meter to the battery post, the other test lead to various points in the circuit .You should get less then .5 volts if you connection and wires are good. I am sending you a link to a video that will show in detail how the testing is done,and a photo I took showing how you test a connection at the battery. If my answer has helped,please click on accept,we don't get any credit unless you do. Thanks,Jerry


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Customer: replied 6 years ago.

Jerry, Thanks for the photo and video. It does help in understanding voltage drop testing. Is it possible to narrow down the faulty ground side of the circuit by putting the voltmeter between the negative battery post and the negative battery cable and then one by one, pulling each fuse untill the reading goes to zero volts?




Expert:  roadsidejerry replied 6 years ago.

Hello Art, I believe you have parasitic drain testing confused with voltage drop testing. To check voltage drips you connect your voltmeter between various connections with the cable and wire connected. To test for a drain condition, you use an ammeter that reads milliamps. I will send you some info on this and n illustration showing how the meter is connected. If you do get an excessive reading, this is when you pull fuse to try and isolate the problem circuit.

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