Great! you are learning where everything is. Have you checked all the fuses? Could you post a picture of the light sockets and show where you have been testing. A few pictures of the wiring on the back side and where it mounts to the frame would be good also.
1994 Class A chassis electrical issue
- Thread starter Rhianntp
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The left picture is a factory GM fuse box. The one on the right was probably added on by the motorhome manufacturer. My wild guess at this point is still a rusty bolt, screw or stud in the rusty frame not providing a proper ground to anything mounted to the fiberglass body that requires a frame ground to work properly. Most likely it is toward or at the rear of the frame. Following the main wiring harness should lead to somewhere on the frame with a wire or more likely several wires attached to it which will be probably a connection that will need to be cleaned and checked. The wire terminals will have continuity but none will have continuity with the frame even though they are secured to the frame the electricity just ain't getting to the clean metal part of the frame. Sounds crazy but it happens all the time especially on older vehicles.
Like I said before things are not always what they seem. The results of turning on and off circuits isn't compatible or giving the results of the tests you are doing, one reason I need the pictures of the sockets and where you are doing the tests is I cannot justify the results. The other thing is that simply getting underneath and following the wires to where multiples attach to the frame cleaning and physically verifying a good ground to the metal frame may solve the majority of the problems of the way your circuits are operating. The results of your testing says the circuit has a good ground, bulb and power yet the the bulb doesn't light. There must be something wrong with the way we are communicating on how to do the tests. Circuits have to have a problem or they don't back feed. Your circuits are back feeding. There are a few reasons that happens. It most usually in my experience is a bad physical ground, a shorted socket or every so often a bad dual element bulb. You have checked and physically looked at everything except the physical grounds on the frame, it is time to do that. Do everything above and let us know what you find. We can do all the trouble shooting but only you can physically do the labor and checks. This is far from the best way to communicate but pictures help and if you have questions ask but don't skip steps when trying to trouble shoot it just makes it harder. We are 9 pages in and just now to a point of checking something that should have been checked first! Lol!!!
highdesertranger
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"I am able to see 2 fuse links under the "hood" a 20 amp and a 30amp.. they both are good."
So you checked them both with your meter, right?
Also that wire I have been telling you about on the starter HAS a fuse link on it somewhere have you check that?
That big fuse block is factory GM. You can see, tail lps, stop haz, and turn bu. have you checked all those with the meter. the first 2 of those should be hot with the key off. the trun bu should be hot with the key on.
Highdesertranger
So you checked them both with your meter, right?
Also that wire I have been telling you about on the starter HAS a fuse link on it somewhere have you check that?
That big fuse block is factory GM. You can see, tail lps, stop haz, and turn bu. have you checked all those with the meter. the first 2 of those should be hot with the key off. the trun bu should be hot with the key on.
Highdesertranger
Yes that is one way, you can also use the volt meter when there is power on the circuit by grounding the negative lead on a known good ground and at the top of modern fuses like yours there two access slots to the metal prongs on either side of the part of the fuse made to melt ( the little shaped section ) if there is 12 volts on one side and the fuse is good there should be 12 volts on the other side. Sometimes the tips of your meter leads need to be ground or filed to get into the metal as the slots are very small. Trouble shooting usually begins with checking the battery for good connections and charge then the fuses.
A hot touching ground somewhere should blow a fuse, or make a circuit breaker click like crazy. How are you measuring the negative side? If the socket is not grounded, and you apply 12v to the positive and the meter between the socket and a good ground you should get voltage, but I don't know if it'll be 12v once it runs through a bulb which will act as a resistor.
Again more progress, we are getting somewhere! Picture #1 the bulb socket in your hand is for a dual element bulb. The low wattage element is the tail lights, the high wattage element is for the brake light and if there is no separate yellow lens the turn signal/ hazard light. One of the terminals in the socket will have power when the running lights are turned on and the other will have power when the brake is activated, intermittently when the turn signal is on or the hazard flashers are working so neither of them are grounds. The bulb is grounded when the pins and metal case that hold the glass part of the bulb on is installed in the metal part of the socket. You should have 3 wires coming out the back, one ground attached to the metal housing in the bulb socket and two powered wires going to the insulated pins in the bottom part of the socket that complete the circuits for the brake and tail lights when the bulb is installed. Place the red probe on the inside of the bulb socket against the outside metal part while the black lead is connected to the shinny metal frame and check continuity , it should be connected and sound. Be sure to let us know what you find. Picture #2 the white wire screwed into the frame is probably the ground for your trailer plug and looks to be rusty metal. Make sure there is shiny metal under the terminal and continuity between the plug terminal and you clip on the shiny metal frame. The large black wire loom that is tucked up in the frame just behind your clip is probably what we want to follow there should be power and ground wires for all the rear lights inside it and some where nearby there will be a ground or several ground wires the exit the loom and are attached to the frame (that is where I believe we will find a problem) as your frame appears to have severe rust. There is a green wire there loosely strung that is probably a brake light wire that has bee spliced into a brake light circuit that will also go to your trailer plug. Picture #3 looks like you did a good job with your test lead, to test it put your meter on continuity and touch the red lead to the clip on the frame, it should sound.
All sockets sound when probed as you asked..the ground wire connected to rust also sounds fine ... The neg wire that would go to the license plate light also sounds ..so does the positive wire there though .is that an issue?
I do not intend to tow anything so have no use for the electric harness to be hooked up at all..would it be smart to just cut if off? Someone installed a brake controller after market as well...would not need that either
I think the problem with the testing is we failed to explain the metal outside of the bulb is the ground and the metal outside part of the socket is where it connects. I believe you have been trying to test for a ground using one of the two pins instead of the outside housing, is that what happened?
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