Headlight sw. problem

Ed ke6bnl · April 26, 2007, 05:50:01 PM

Here is my problem, I have no instrument panel lights. I have a working dome light and just found out I have no tail lights working. The fuse that is listed as being the instrument light fuse has tested ok but there is never any power going to it with the headlights on, the ignition on, I show no power to either side of the fuse. All other fuses have power at one time or another with the ignition sw. on. This is an 80 GMC dually 1 ton pu. I am not clear how the power is fed to the light sw. and its rehostat. This is my thought, the power is fed to the light switch and goes through a resetable breaker to one side of the rehostat to the other and then to one side of the fuse and out the other to the lights. My plan so far is that I need to change out the light switch. Am I going in the right directions. Can I feed power to the fuse for the instrument light and will that test the instrument lights?? kinda confused and the wiring diagrams aren't helping me much. Thanks for your suggestions. I have head lights and signal lights..

Dave · April 26, 2007, 06:22:28 PM

Hey Ed being a fellow ham radio operator dont you know your kinda groping in the dark with out a schematic? I never try to figure out this new junk without one.. Actually whenever anyone asks me about electrial i tell to get a manual and then bring it over..
Dave

WZ JUNK · April 26, 2007, 09:16:17 PM

Quote from: "Ed ke6bnl"Here is my problem, I have no instrument panel lights. I have a working dome light and just found out I have no tail lights working. The fuse that is listed as being the instrument light fuse has tested ok but there is never any power going to it with the headlights on, the ignition on, I show no power to either side of the fuse. All other fuses have power at one time or another with the ignition sw. on. This is an 80 GMC dually 1 ton pu. I am not clear how the power is fed to the light sw. and its rehostat. This is my thought, the power is fed to the light switch and goes through a resetable breaker to one side of the rehostat to the other and then to one side of the fuse and out the other to the lights. My plan so far is that I need to change out the light switch. Am I going in the right directions. Can I feed power to the fuse for the instrument light and will that test the instrument lights?? kinda confused and the wiring diagrams aren't helping me much. Thanks for your suggestions. I have head lights and signal lights..

I would change out the switch. I guess that at one time everything was working and now it is not. The headlight circuit should be protected internally in the switch with a circuit breaker. Your tail lights and instrument light are powered through the switch but then fused at the fuse box before the power goes on to the lights. My guess is that something mechanical is broken inside the switch and it is no longer making the internal contacts to route the power out.

My best guess.

John

Pep · April 26, 2007, 10:15:35 PM

What you suggested is fine...Just make up a test probe so you can tap off another live circuit. Just include a 10 amp fuse in your test probe, just in case you short it out to ground. By doing that, you can eliminate a lot of the wiring. If it still doesn't work, keep going futher towards the rehostat.

Ed ke6bnl · April 27, 2007, 02:49:16 AM

Quote from: "Pep"What you suggested is fine...Just make up a test probe so you can tap off another live circuit. Just include a 10 amp fuse in your test probe, just in case you short it out to ground. By doing that, you can eliminate a lot of the wiring. If it still doesn't work, keep going futher towards the rehostat.

Well here is the good news so far, I work nights and so by myself during the daylight I could not press buttons and look behind the truck and even see the lights for the instrument panel. Before going to work tonight i went out and used my power probe tester and energized the fuse that had no power for the gauge lights and energized it and the lights for the gauge came on and I could see some of the clearance lights on from the cab where glowing. So tomorrow mourning I will pick up a light sw. and tear into the dash to install it. thanks for all your advice ED

WZ JUNK · April 27, 2007, 06:16:49 AM

Quote from: "Ed ke6bnl"
Quote from: "Pep"What you suggested is fine...Just make up a test probe so you can tap off another live circuit. Just include a 10 amp fuse in your test probe, just in case you short it out to ground. By doing that, you can eliminate a lot of the wiring. If it still doesn't work, keep going futher towards the rehostat.

Well here is the good news so far, I work nights and so by myself during the daylight I could not press buttons and look behind the truck and even see the lights for the instrument panel. Before going to work tonight i went out and used my power probe tester and energized the fuse that had no power for the gauge lights and energized it and the lights for the gauge came on and I could see some of the clearance lights on from the cab where glowing. So tomorrow mourning I will pick up a light sw. and tear into the dash to install it. thanks for all your advice ED

The light switch should not be difficult to replace. I have not done one just like yours lately but you should be able to do it in a short time. First disconnect the battery. The switch lever is removed by pulling the lever out until it stops, pushing in on the spring loaded button on the side of the switch and then pull the switch lever out. Remove the trim nut on the outside of the dash and then pull the switch and wiring down from under the dash. Unplug the old switch, plug in the new and reassemble. I hope it goes that easy for you but sometimes there are some glitches. I will pm you my phone number and you can call me if you need some help.

John

kb426 · April 27, 2007, 06:46:30 AM

In recent years, all GM vehicles have the dash and tail lights on the same circuit. I have no idea why it's done that way other than if you have no dash lights, you should know you have no tail lights. I've had friends that had to replace some relays under the dash. I don't know what specific item they needed.

Ed ke6bnl · April 27, 2007, 07:04:39 AM

Quote from: "kb426"In recent years, all GM vehicles have the dash and tail lights on the same circuit. I have no idea why it's done that way other than if you have no dash lights, you should know you have no tail lights. I've had friends that had to replace some relays under the dash. I don't know what specific item they needed.

My old econoline with its limited fuse system had this same set up and I am told the same that it was done so you where aware that you had no tail lights. i would be more concerned that I did not have any brake lights though.

BFS57 · April 27, 2007, 08:46:10 AM

Hello;
I'm the guy that has the same problem on my 57 chevy!
The "made in mexico" headlight switches aren't worth poop!
The real problem is: the tail lights (rear park light circuit) also feeds the license light. Now, in my case, the license light got wet and shorted the circuit making the tail lights and dash lights go out. This is because there is a set of "points" inside the switch.
Now, I have the replacement switch which I did some surgery on, opened it up on the side and back where these contacts are, removed the contact, bridged the two points with a soldered wire with a 20 amp fuse on it! I also created a "pig tail" with a 10 amp fuse on it that connects to where the dash lights come from off the switch and the wire leading to the dash lights goes on the other end. I also rewired the license light with a 10 amp fuse (in the trunk area) on it so if it gets wet again, it should blow the fuse there!
This seems to be an on going problem as when I purchased my car, the tail lights and dash lights were "hot wired" to the ignition, so when you started the car (day or night) the tail lights and dash lights were on!
Don't know what else to ad except use good judgement and keep in mind that most parts you buy these days ain't worth the materials there made of!

Bruce

Ed ke6bnl · April 27, 2007, 09:09:47 PM

well first off thanks for all the suggestions, I found there are two feeds for the light switch and the one that feeds the tail lights and gauge lights did not have power I tried to trace the two yellow wires and had no luck I then splice in a fused hot lead to the yellow wires and now all is good. The new light switch did not help but while it was out I replaced it. I am sorry I could not find the real source of the problem but it is all working now. I learned a lot on how this portion of the electrical system works. This will all come in handy when it is time to properly rewire my 50 F1 truck. I still will be in new territory when it comes time to do the steering column work but some of the new kits are plug and play but best to have a well grounded understanding of its wiring(sorry about the pun). thanks again ED

WZ JUNK · April 28, 2007, 07:53:10 AM

Quote from: "Ed ke6bnl"well first off thanks for all the suggestions, I found there are two feeds for the light switch and the one that feeds the tail lights and gauge lights did not have power I tried to trace the two yellow wires and had no luck I then splice in a fused hot lead to the yellow wires and now all is good. The new light switch did not help but while it was out I replaced it. I am sorry I could not find the real source of the problem but it is all working now. I learned a lot on how this portion of the electrical system works. This will all come in handy when it is time to properly rewire my 50 F1 truck. I still will be in new territory when it comes time to do the steering column work but some of the new kits are plug and play but best to have a well grounded understanding of its wiring(sorry about the pun). thanks again ED

The GM style light switches that I buy from Haywire are much like the one for your truck. When I add the GM plug connector to the harness for the switch, I have to add a jumper wire from the main feed to a terminal on the plug to power the dash and tail lights. So if I understand you correctly, you did the same thing on your truck.

John

Ed ke6bnl · April 28, 2007, 10:35:10 AM

Quote from: "WZ JUNK"
Quote from: "Ed ke6bnl"well first off thanks for all the suggestions, I found there are two feeds for the light switch and the one that feeds the tail lights and gauge lights did not have power I tried to trace the two yellow wires and had no luck I then splice in a fused hot lead to the yellow wires and now all is good. The new light switch did not help but while it was out I replaced it. I am sorry I could not find the real source of the problem but it is all working now. I learned a lot on how this portion of the electrical system works. This will all come in handy when it is time to properly rewire my 50 F1 truck. I still will be in new territory when it comes time to do the steering column work but some of the new kits are plug and play but best to have a well grounded understanding of its wiring(sorry about the pun). thanks again ED

The GM style light switches that I buy from Haywire are much like the one for your truck. When I add the GM plug connector to the harness for the switch, I have to add a jumper wire from the main feed to a terminal on the plug to power the dash and tail lights. So if I understand you correctly, you did the same thing on your truck.

John

That is what I am saying. I did get the hot from the engine compartment but what you did is similar but the plug and its wires would not drop down far enough from under the dash to make those connections at the plug. Well I went out last night and checked it all out when it was dark and it was all working fine. Thanks for your offer of help. Ed

UGLY OLDS · April 28, 2007, 10:40:32 AM

Hey guys...After seeing more & more posts about electrical "issues & adventures" people are having with cars that other folks have wired, an idea came to mind..

While I don't know the boards policy about vendors & suppliers,( Frank..feel free to remove this if improper ) , Ron Francis has a very good troubleshooting "guide" & tech manual" in the back of his catalog...Lots of advertising for his products, BUT, lots of good basic auto electrical info...90% of the info comes under the heading of "snow is cold" for those of us that have been building & repairing cars for ever, but LOTS of good info for the guys that are just starting out or whose expertise is in other areas...( Gee, Isn't EVERYBODY a car EXPERT ) :?: The best thing is that they are free...Go to his website...Plug in your name & info...He mails it to you...Again...Not a plug for him or his product...Just a heads up...

enjenjo · April 28, 2007, 02:20:22 PM

No problem with the francis post.

Another tip, most aftermarket harness are based on a 70's GM schematic, and in that era, most of them were wired the same, with the same colors. So most any GM wiring diagram from that era will be an aid to troubleshooting.

UGLY OLDS · April 28, 2007, 03:58:28 PM

Quote from: "enjenjo"No problem with the francis post.

Another tip, most aftermarket harness are based on a 70's GM schematic, and in that era, most of them were wired the same, with the same colors. So most any GM wiring diagram from that era will be an aid to troubleshooting.

For those needing the " E-Z Wire " instruction manual & schematic , it can be found here & downloaded :

http://www.clparts.com/faqwiring.html#dl_ez