I'm having problems with my 93 pickup in the electrical system. My stop lights work, but my taillights do not, my front signals work but the rear do not. my right front high beam does not work. My dash lights do not work except for the shift position light(its an automatic) Also my license plate light does not work...what I'm wondering is do al these problems relate to something simple like a relay or do I need to look at having the whole electrical system redone? I have checked all the fuses and none are blown, also I have replaced the 2 front lights at the same time. so I know its not that. Any suggestions on where to start would be appreciated. TIA Matt Noyes
I would start by obtaining a service manual (I have a new one I would sell you $15 + shipping), or visit your local library to look at one, and check the wiring diagram. Following the circuits one by one would allow you to get to the root of the issue.
Louis--
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How did you check them, visually? I've seen hundreds of fuses that the owner swore they had "checked" which looked fine, were not "blown" but wouldn't conduct electricity. the only way to checl them is with a test light.
Headlamps? sounds like you have multiple problems, probably a bad headlight switch and a dead dash lamp controller? I'd get a test lamp and start looking for power and ground.
DON'T use a volt meter, they put no load on the circuit and while there may be milliamps of current and 12V, there isn't enough current to power the lamps. A test light is cheap and will always show you if there is "power" where you are testing. I've watched too many people get lost in cars wiring using a voltmeter, I never use one myself unless the testing procedure demands it, i.e. computer curcuits.
The above is good advice. A visual test alone can be very misleading. Using the test lamp as above, or an Ohm meter to check continuity through the fuse will also work. The beauty of checking the fuse in circuit is that you are also testing the wiring to the fuse, and the fuse holder. A test lamp with the long sharp point and the clip for ground is the most useful.
Correctly used a voltmeter usually isn't too misleading if properly applied, and the results correctly evaluated.
Voltmeters used when measuring AC can be very misleading. Wires that aren't live can have voltage induced into them when run near a live circuit. The more current the live circuit carries the more pronounced the effect on the wires surrounding it. The problem is most pronounced where a high impedance voltmeter is used. The average digital voltmeter can have an input impedance of 20 meg Ohm and up. This allows measuring a circuit where little loading of the circuit takes place. This is useful where the circuit is an electronic one with low capacity, and connecting a low impedance load would alter the circuit characteristics to the point of rendering it inoperative, or altering the logic level where the input is unreliable. A wire with no voltage feed, run close to a live circuit for a distance can indicate substantial voltage when measured with a digital meter, but if a load (lamp, coil, etc.) is placed on the wire in addition to the digital meter the indicated voltage will drop to zero. In the above example if you desire to use a volt meter you could use a cheap analog meter (with a moving needle) which has an input impedance near 2,000 Ohms or so. This will allow more accurate readings at times than a digital meter where lack of circuit loading is an issue.
A voltmeter can be quite valuable for trouble shooting electrical systems. One use I find very helpful is a voltage drop test. On a circuit that I'm having trouble with I start at the battery and place the leads one at the battery, and the other at the first connection point in the circuit. With the range scale set very low (2 volts or so on a 12 volt system) I check for voltage drop. If the reading is more than a few millivolts there is likely a problem with a connection at that point (broken partially connected wire, dirty connection, etc.). I keep moving the leads up the circuit testing each wire length and connection. When I get to a point where the needle swings full scale I've usually found the problem (bad connection, switch, fuse, wire section, etc.). If you have a wiring diagram the process goes very quick, and the problem is usually found in short order. Without a wiring diagram the process can take enormous amounts of time, and a bad element (usually the hidden one responsible for the trouble) can be easily overlooked.
The problem is they put zero load on the circuit and I've seen severely corroded conections that wouldn't begin to operate even a dash bulb show
12V with a digital volt meter. The higher load analog type aren't as bad about this but most people try to use the digital type.
Oh they are useful but I think for trying to diagnose things like tailights that don't work at all, a test light (the screwdriver looking kind with a ground wire and a sharp pointed end) are a much better tool to use. It too easy to get lost using a volt meter and using a test light is pretty simple, either it lights up or it doesn't and tests both for voltage and amperage at the same time.
But as you said without a wiring diagram and the ability to read it, you're probably not going to have much luck solving the problem unless you just get lucky.
A voltmeter is like any other tool. It needs to be understood, and applied properly. If one were to "play around" a bit with both a digital, and analog meter investing the time to learn the idiosyncrasies of each it would be time well spent. Using a volt meter like I described earlier for a "volt drop" test would illustrate exactly the amount of voltage dropped, or lost by each element of a circuit. The volt drop test will, if executed properly, locate precisely where the problem element in a tail light, or most other circuits as well, is. It will also alert of brewing trouble (increasing levels of resistance while the circuit still operates) in a connection where the test light indication might not be as easy to pick up on.
The advantages of the test light are ease of operation in trouble shooting (very low learning curve), compact size (easy to store), and usually very tolerant of abuse. It's a good go, no-go type of tester.
For vehicle electrical system trouble shooting I prefer to have access to both. If I had to choose between the two and only carry one I would probably opt for the test light.
Louis--
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Someone sent me a reply to this thread today, but for some reason it was mangled to a point where the message and sender information was unintelligible.
If you will resend the message so I have a readable copy I would appreciate it.
Thank you.
Louis--
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Sure, but in my experience with thousands of customers over the years, most don't take the time to learn how to properly use them and come in proclaiming how they checked this and that with a voltmeter and then want to argue after I find the real problem that they already checked that and it's fine etc etc..
How many people are going to be checking circuits that still operate? :-) As far as finding the source of the problem, it's just as easy to search for the place where there is still power along the problem wire as doing a voltage drop test, in fact it's easier as you only have to probe with one lead not connect two.
Exactly, for 99% of electrical problems on a car, it's what most people should be using.
The problem again is people don't have both, most don't understand how to correctly use a volt meter (load the circuit before testing it..) and are just trying to use what they have at hand. Again IMHO for most wiring issues like the OP's a voltmeter is overkill and will just confuse most people unless they really think through what they are doing and then why make things more complex an they need to be unless you just enjoy complex problems!
I would be tempted to offer the old sage advice to "never argue with a moron", but if you next have to collect money for services the options are somewhat limited. :-]
You gotta love someone that pays you good money for your knowledge or services, and then argues with your results!
If the problem is at a single point I would tend to agree with you, but where multiple degraded connections or points in a single circuit are an issue, the combined voltage drop could limit the voltage available to a high current devices, but still pass enough current to light a low draw device such as a test lamp.
I agree, but I still maintain it's worth the effort learning to correctly use a volt meter for the occasional issue that a test lamp wont address.
I don't look for, but enjoy being able to solve the occasional complex problem. :-]
I agree with most of your last paragraph with the exception of "loading the circuit". Implementing a voltage drop test can be accomplished even with a high input impedance (digital) volt meter. Loading of the circuit is primarily an issue where measuring AC voltage, and in some instances with DC at some point along the circuit to ground. When performing a voltage drop test loading of the circuit, at least from the perspective of a volt meter, isn't an issue.
Louis--
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After intending to do so for some time I finally checked out your web site. I was very impressed. Particularly with the pictures accompanying the articles. They were clear, of high quality, and added a lot. I especially liked the Z FAQ article.
Louis--
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Hi Matt, I had a similar problem with my 95. It turned out to be a problem with the tail-light assembly. I saw problems in the rest of the truck so I never figured it was all from the tail. I found out there was a recall for the tail-lights. Once my dealer fixed them for free I have had no more problems. Wish I figured it out sooner - I burned through
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