Dim headlights

[Eric]

Hey guys. I recently purchased a 97 s10 2.2 liter. I noticed the other night that the headlights are dim. Not one but both, and they seem to be dimmed about the same amount. It makes it pretty hard to see while driving. I can see but it’s like a 10 foot in front of you kind of driving which is not safe. I have yet to replace the lights yet because I’m wondering if this is an electrical issue. I’m not very good with a multimeter but I do have one. Am I right in thinking that a simple check at the connector of one of the lights would rule out/ confirm the low voltage to the lights? What should these voltages be? What would a normal voltage drop with the headlights on at the connector be as compared to what I get at the battery, which I believe was a 12.8 or somewhere in that neighborhood. I know my battery is good I just pulled it out of my 98 Grand Prix that everything works just fine. Thanks for any input. I plan on grabbing another headlight today to check it out but since both are dim I just don’t think it’s a bulb issue.

Topic

[jason]

you need to check the voltage at the battery with the engine running it should be 13.5 to 14.8 it sounds like you may have a alternator not putting out wright.

[dan]

with hamby on this one, the heart of your electrical system is the battery and the alternator, check those first, if those are bad everything can screw up, the battery should be putting out 12.6V or around that number a little more or a little less give or take, and as hamby already stated if your vehicles running voltage is not 13.5-14.5V then there is either a issue with your alternator or the connections.

also check the connections too your battery, make sure the terminals are tight and not corroded, check the grounds, make sure they are tight and not corroded, and if all checks out here check the wiring too your lights, any connectors make sure they aren’t corroded and they are correctly installed, check the ground for your lights and make sure it is snug and clean.

also here is this.
http://www.ericthecarguy.com/faq/solving-automotive-electrical-problems

good luck and keep us posted.

[Eric]

Okay guys, I’ve done some tests. I had my alternator checked and it tested good… I believe it was 14.25 volts. My battery tested good at 12.83 volts. Now here’s the thing, I turned on my lights and checked the connector for the headlight and it only read at 10.61 volts. A big voltage drop, or maybe a normal one… I’m not sure. I’m pretty sure it should read higher than this am I right? What’s my next step/ probably cause? I will head back out right now and check for bad grounds and re-ground the wire. One thing i did do is I hooked the positive end of the tester to the headlight plug and then I placed the ground wire of the tester to the negative battery cable. This read at 12.83, the same as the battery voltage. So… A bad ground? And I’ve grounded the tester on a couple of other places on the engine and they all read 12.83… Does this indicate that the bad ground is at the lights themselves?

[Bill]

I think you’re on track with the bad ground theory. I believe the grounds are under the hood on the rad support. Also make sure that the battery ground connection is clean where it attaches to the body of the truck. Usually the small wire that runs along side of the negative battery cable.

[Eric]

If grounding the negative lead on the engine reads the exact same as on the battery terminal does that mean that the main ground wire is fine?

[Eric]

I still can’t seem to find the ground for the headlights. Is there just one or one for each light?

[Eric]

I think I’ve figured out which wire should be the ground on the socket. To test this can I take a jumper wire and ground it to a known good location on the engine then touch it to the ground wire on the headlamp. This should make it light up fully if the problem is a bad ground right? then I should be able to splice that wire into the existing connector and make a new ground. Am I right in thinking this or would I mess something up by doing this? Sorry for all the questions but I am not good with electricity

[Lorrin Barth]

One of the wires from the headlight plug should connect to the metal shell of the truck in the vicinity of the headlight. There will probably be one for each side. Anyway, if you can get to them, cleaning the connection is easier than running a new wire.

I don’t know if it is still true but the last GM vehicles I owned had pitifully small wiring going to the headlights. I upgraded one of these cars to the largest wiring I could fit in the headlight plugs and the change was amazing. That combined with a couple of other things I did produced the best headlights I ever saw on a car and this still using legal bulbs.

[Bill]

There should be a ground from the battery to the body of the truck. The headlights a grounded to the body. To make it easy for you ,you could take a piece of wire or even a booster cable and connect one end to the negative cable at the battery and after cleaning a spot on the body to bare metal you can complete a ground connection to see if the lights are brighter.

If there is no difference then the battery ground is not the problem. If the lights are brighter then the battery needs to be grounded to the body.

[Eric]

Well turns out it’s a hot wire problem. I took a wire and grounded the bulb directly to the negative on the battery. It had no effect. I even did both lights at once and nothing. But as soon as ran a wire from the positive terminal of battery to the positive side of the battery, Bingo! Light came on bright. So what should I check now? I’m thinking either a bad wire or a switch possibly? What are your opinions?

[jason]

you know these s10 trucks were none for having bad ground problems anyway I have had about 6 of these trucks from 1992 to 2000 and really all of them had ground problems form the fuel system grounds to the light grounds even computer grounds and on all of them I have just added a few body grounds and it solved a lot of trouble.

[Lorrin Barth]

[quote=”ewhitaker0020″ post=100078]Well turns out it’s a hot wire problem. I took a wire and grounded the bulb directly to the negative on the battery. It had no effect. I even did both lights at once and nothing. But as soon as ran a wire from the positive terminal of battery to the positive side of the battery, Bingo! Light came on bright. So what should I check now? I’m thinking either a bad wire or a switch possibly? What are your opinions?[/quote]

I first did the above test on a 1970 Ford Maverick I owned (positive battery post to headlight) and discovered bright headlights for the first time on that car. Back then vehicles had no headlight relays so I installed one next to the battery. It was a big improvement.

Then I owned two firebirds and they both got headlight relays. When my wife had eye problems and had trouble seeing at night I upgraded the headlight wiring on her car and replaced all the sealed beams. That car had super headlights.

Anyway, I’m thinking you are looking at normal GM engineering for the period – crummy headlight wiring. The lights on that truck probably have always been dim.

Well, they can be fixed if you want to do the work to do it.

[Eric]

What do you suggest I do to fix this wiring issue?

[spelunkerd]

Here’s a practical opportunity for you to measure voltage drop and find the source of your extra resistance at the same time. As others have mentioned, most headlights are controlled by a headlight relay so the control wiring doesn’t have to be large gauge wire. I would search for a wiring diagram and find that relay, then measure voltage drop while current is flowing at as many places as you can find. BBB industries have posted some free wiring diagrams for many vehicles, you could look there if you need to. The wiring is a little more complicated than one would think because of the requirement for lights to work even when one side burns out, and of course you’ve got high and low beams. I would pay close attention to the connectors behind each headlight, looking for evidence that one of the connectors might have overheated (yellow color, melted plastic, etc). The extra heat behind the light can melt solder, increasing resistance which in turn causes more heat, eventually melting the connector. The other more rare and slippery issue is the off chance that you’ve got another source of current draw that is overwhelming your alternator, allowing system voltage to drop when under full load, robbing the headlights of power.

[Author]

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