The Stovebolt Site Forums The Shop Area The Electrical Bay Dome light wired backwards?

Ok, so I have been slowly replacing all the chewed up wires in mt 62 GMC 3/4 ton, (cab was so full of rat poops that it was up to the dash) I'm pretty close to having it all going just need to finish fuel gauge and brake lights, blinkers, and dome.

The wire for the dome light was pretty much gone so I ran new wires up to it but was not sure what wire went to what side and figured I got a 50/50 shot. hooked it all up and hit the switch, but nothing. I then flipped the bulb around and it lit up but with the dimmer in the off position. I figured I had the wires backwards, so I swapped them around, and flipped the bulb again, and same thing happened just this time the bulb had to be put in correctly to light up (with switch still in off position).

I left it that way for 2-3 days with the switch in the on position (with the light off). This morning when I went out to the truck for round 2 the battery was was almost all the way dead, it just cranked over 1 time then nothin'.
I have it on the trickle charger now and will start again this evening.

No combo of swapping things around got the dimmer to work correctly it's only on in the off position and when I roll through the dimmer nothing happens.

The bulb is a LED DC-12 error free 3 SMD 42mm dome trunk cargo area light. seemed to fit well and lit nice and bright just in the wrong position.

Would this be a problem at the switch itself? I know the PO methed up the wiring quite a bit before the rats got to it all. (some of the intact wiring was really weird with alot of "extras" like 3 horns and 4 antennas 2 blinker switches doubles of most gauges and brake lights that ran separate from the original tail lights that appeared to be from a trailer) The rest of the switch functions properly with all other lights working (besides blinker and brake)

I would not be surprised it the wiring at the switch was backwards, but it does not appear to wired by the PO as his stuff was pretty obvious. Although the switch appears to have stock wiring he may have just done a better job that time.

The dome light has 12volts hot to it all the time, the door switches and dash dimmer ground the other wire to complete the circuit. It sounds like you have a short to ground and that is keeping the lite on, also draining the battery if the hot is shorted.

That makes perfect sense, when I connected it all I left a section of original wiring coming off the back of the dome light and down towards the fuel tank, I didn't want to remove the dome light itself and risk damaging the brittle bits of it. I would imagine that even though its a slim fit a rat must have squeezed up there and chewed a spot in there that's grounding out against the cab.

I will remove the entire dome light and run brand new wires through the whole deal. I hadn't been leaving any original wiring in place if any section of it was damaged except for this and now I know why.

So you are aware, almost all L.E.D. bulbs are polarity sensitive.

I figured as much, that's why when I thought I crossed the wires I flipped the bulb.

I'm scared of breaking the tabs that hold the dome light itself in the cab, I was able to un-clip one of them with some light wiggling and soft tab pushing. sprayed some oil on it and let it sit overnight, will try to get it the rest of the way off without breaking those tabs off.

Well, I pulled the wires and dome light out, hooked it up the new wires (took a minute to figure out which orange wire was what but a small piece of the ribbed/plain wire stuck in the old plug helped out along with a wiring diagram I got here). hooked up the light itself to the wires before install to make sure I do it right the first time, and it responds same as before. I used a test light on the wires as well (so i don't have to worry about the aforementioned polarity of the LED light) but to no avail. Same results all around.

Looking at the switch itself it seems untouched, sometimes it has the occasional flicker of the headlights but a light wiggle stops that. So I don't think that my problem is there.

My fuse block however is a different story, I think the problem could be closer to here. I have noticed some damage to it but it seemed minor mostly (except for the spot light fuse).

As I follow the ribbed/plain black wire from the light itself it goes to the 3 pin connector below the fuse block I think one orange wire goes to the fuse block, and the other orange wire goes behind the fuse block and up to the switch. there is a third white wire coming from behind the fuse block along side the 2 orange ones, so now I'm a bit confused.

What is it I'm missing here? it grounding out made sense and the wire wasn't pretty, but with that replaced I would think my problem would have gone, along with that wire.

I will try to remove the fuse block later and see whats goin' on behind it. I have a strong feeling that I must be grounding out back there.
While I'm back there I wanted to check the back of the male tab for the fuel gauge, I was reading F all the time then I replaced the grounds at gauge and sender and now I'm always on E even with full tank.

does anything on the fuse block look altered or non-original?

Think about replacing that LED with a regular bulb. LED's draw so little current that you can get real strange errors in older slightly corroded automotive circuits that are designed for amps, not milliamps. Also check that you have the not hot wire from the dome light going to the correct terminal on your switch.

Mark

I used a regular bulb as well with the same results. Also cleaned the tabs the bulb makes contact with.
I will take a closer look at the switch and chase some wires with the diagram tomorrow or the next day, I have looked at it and all the colors matched up to the diagram but both wires for the dome are orange so I will need to chase that down.
Only reason I thought it was coming from the fuse block is because I don't have blinkers at the moment or brake lights (although my tail lights do work), but some of the under bed wiring was obviously altered over the years as well as the blinker mechanism so those may all be separate issues.

Ok, so I followed the wires down and saw that at the plug with the 2 orange a 1 white (or natural).
White (or natural) goes up to the top of the switch on the drivers side. (terminal 7 on the switch)(this is the wire that at the 3 pin connector turns into the ribbed black wire).
The 2 orange wires lead up to the bottom of the switch on the passengers side closest to the driver. (terminal 6 on the switch)(wire at 3 pin turns from 2 orange to 1 plain black HOT)

From what I can tell it is wired properly and all the wires are intact and not grounding out that I can see.

I also grounded out the black ribbed wire (while using a non LED bulb).
With the switch in the Off position the light was on before grounding and brighter after grounding.
With the switch in the On position the light was off before grounding and on after grounding.

I'm thinking it may be in the switch itself? maybe if its grounding out internally that would produce the symptoms I'm experiencing.
Would rebuilding the switch be of any benefit or am I just spinning my wheels here?

Ok, I'm going to put the dome light back in and solder the wires back together. (at least now I know what ends ribbed/plain go to).
I'm just gonna leave the bulb in the ashtray and pop it in when I need it.
I'm going to move on to brake/blinker lights. Maybe I will stumble onto the answer later, if so I will post here for future reference.

Well without the bulb in place there is still a power draw. battery was almost dead this morning. Maybe my power draw isn't coming from the dome light, but it wasn't a problem before I did stuff to the dome light.
all I did was put a bulb in it and replace the section of wire from light to the plug right below the fuse block. The wires were definitely grounding out before, but should not be now.

The mystery continues...

could the switch be draining the battery if it was grounding out internally?
with it in the off position (rotated all the way to the left until it clicks) its all on, could it draw power without the bulb in? since it's not a complete circuit i thought it wouldn't really draw power but I'm open to being wrong.
with the switch in the on position (clicked over to the right but with the switch not rotated fully to the right, just to where it clicks) I get no light but still seem to be drawing power. Same results as the switch is rotated to the right the rest of the way there is no change.

Man Oh Man, what a saga. I can help if you will restate what is wrong with what.
1. How are you testing what you call a "draw" ? with what meter? set to what? Test probes touching what? Be specific so I don't have to ask a million questions.
2. Using ONLY a known good regular incandescent bulb, what is the problem with the dome light? Let's stick with the dome light issue first because it is so easy.
3. If your problems are already solved or don't wish to use my methods. No problem.

Thank you for the response, problems not solved and I'm open to any method (wouldn't know very much if I wasn't)

so I'll start at the beginning and finish at the end.

I noticed while cleaning the grounds on the fuel tank sending unit that the wires for the dome light where chewed through. I followed what was left of them and it seemed pretty straight forward.

I soldered some wire to what was left of the plain/ribbed wired at the light and to the ends of the plain/ribbed wire at the plug that is below the fuse block.(I followed the wires past that up to the switch and they were in good condition and followed the wiring diagram.

Once I finished that I put in an LED bulb. It lit up the second I put it in. I went to the switch thinking I left it on but it was in the off position (rotated all the way to the left).

I then flipped the LED bulb around thinking I had crossed the wires somewhere along there and it stayed dark the whole time.

I then tried a regular bulb, It stayed lit up with switch in off position and turned off when the switch was turned.

next I cut the wire I had previously soldered and swapped it around to no avail. Same results.

Then I grounded out the plain wire, with the regular bulb and it was on in all positions with some flickering as I rotated the switch back and forth.

that confused me so I put it all back together according to the diagram and just left the switch in the on position to keep the light off ( I was using the LED at this time because it was much brighter than the regular bulb and I was using that to read my wiring diagram).

the next morning my battery was dead (it's a fairly new battery and has never been weak or dead after just 1 day). I assumed it was the dome light draining it even though the light stayed dark.

I charged it over night and it started no problem. I popped the bulb out an left it like that (I figured I would just stick the bulb in when I need it seeing as my dome light has no lens).

next day battery was very weak, the truck started and the generator did it's job but I can tell somethings not right and it's likely the thing I just changed.

now I have the truck on a 2-amp charger to sustain the battery while I investigate.

I have a decent multi-meter but have not used it to check yet (Christmas presents ate my garage). I will dig it out tomorrow morning.

I'm at a loss here. It feels like it must be grounding out somewhere but all the wires seem intact that I can tell (the only section I have not looked at is behind the fuse block but I highly doubt that those are damaged based on surrounding wires (I don't think the rats got back there).

thought maybe the switch but all other functions of it work normally and it would seem odd for just that part of it to not work properly.

Your dome light and the battery draining may not be related issues
I suggest you debug them as two unique issues


Dome light
Your switch is still a switch no matter what direction current flows
The switch physically has to be oriented so that off is aligned with the housing the wires on the switch can be either way and the circuit will work correctly.


Battery drain
Start at batter and follow the current,
check the voltage regulator, the cut out coil could be sticking shut
Engine off check for voltage at the generator, everything should be 0V at generator if not that’s where your battery is draining.

-s

Forgive me for being blunt, but it's time. I hoped to avoid the big long rambling answer and story again.

What you have done to investigate is not what I asked. I also must ignore your assessments so I can think on my own with pointed questions. I wanted to start with questions 1 and 2. They are the beginning of how I can help. Just need those answers to get me started. Lets try it again. Short, sweet and make sure you answer the two initial questions accurately. You don't know where I'm going yet and either do I. So don't guess.

I helped you with your cluster and I will help you here if you will slow down and let me guide you.

Here they are again:

1. How are you testing what you call a "draw" ? with what meter? set to what? Test probes touching what? Be specific so I don't have to ask a million questions.
2. Using ONLY a known good regular incandescent bulb, what is the problem with the dome light? Let's stick with the dome light issue first because it is so easy.

@2ManyTrucks- I thought it may not be related,just thought I should check where I changed stuff first.

@bartamos- sorry for my rambling,
1. Have not started probing around yet. Just this morning got enough Christmas stuff wrapped to access my toolbox.
2. Using a brand new regular incandescent bulb, switch turned all the way to the left, clicks at end of rotation (to off position) the light turns on.
switch turned all the way to the right past the click then almost a full rotation (to on position) the light turns off and is dark (no flickers) through entire rotation.

again, I'm sorry about my long rambling stories.

1. You said: "Well without the bulb in place there is still a power draw". That statement is what I am asking about in question no. 1.
2. You are mistaken: Turning the headlight switch knob to full left (CCW) is the dome light ON position. Once it leaves that position, the dome light goes off and the rest of the rotation to the right is dash light dimming.

So what's the next problem? Remember...short and sweet. Don't want your tests or diagnosis, just the next complaint. One at a time. Then I will ask a few Q's and suggest a procedure.

Sweet= precise

I will assume that in the statement about draw is that you were just reading 12V at the dome light socket. As others have said, there is 12V there all the time. That is normal. Draw would be the wrong word. Draw means measuring amp draw/current load when using the amperage setting on a meter. That's why I asked my question the way I did, to see exactly what you were measure and with what settings to be able to say you had a "draw" somewhere. You are doing just fine. Not trying to be hardazz, but if folks are not versed on electrics, it can throw off the person trying to help and make me make mistakes.
If you meant something else, please advise full answer to no.1.

Thank you for correcting my mistake. I was under the impression that the rest of the rotation was for the dome (I listened to my old mechanic friend who is more of a benz guy).
I was aware that it's 12v at the dome light all the time. I get a reading of around 0.2amps regardless of switch position at the dome light.

I know I'm not well versed at electronics but I know just enough to be thoroughly confused by this.

thanks for working with me I know it's not easy to decipher my ramblings.

OK no problem. Here is question 1 again.
1. How are you testing what you call a "draw" ? with what meter? set to what? Test probes touching what? Be specific so I don't have to ask a million questions.

multi-meter set to 10amp test probes to each tab of dome light 0.2amps stays consistently while rotating the switch on/off.

So the black test probe to one tab and the red test probe to the other tab at the same time? Meter set to DC and red plug to amp port on meter and black plug to Common port? and 10A scale. 0.2 would be 200 Ma.
But need to know how each probe lead was connected to the light tabs during each test. You may or may not have detected a parasitic leak. Back when you did this test you thought knob at far left was off. But I see you tested with switch on and off and got same reading? That's why I'm asking specific meter lead placement for each lead during test. Trying to confirm if you have a leak.
There is a better way to test for a leak. We will go into that later.

Did the battery get drained overnight with no bulb in dome ? Is this a known good battery?

A shorted wire usually causes a fuse to blow. Not the usual cause of battery drain. That is more of a power left on to a bulb, a switch not turning off all the way, radio memory, diode in alternator, security system light and etc.......and a BAD BATTERY!!!!!!!

yes black probe to the tab that has plain/nat wire and red to other tab (ribbed/orange (hot) at same the time meter set to DC and yes red to amp port black to common. connected with those little alligator clip style probes (I wiggled them around a bit and made sure it's making good contact). Rotated knob and watched the multi-meter no change.

battery was drained overnight, only enough for it to turn over 3-4 times without the bulb in place (also had the switch in OFF position, though I had it all backwards I left it in what I thought was ON because that turned the light off)
battery is less than a year old and reads 12.8v consistently when it's not in the truck (only had it out for about 3-4 days). so I assume the battery is good. it's still under warranty so I can take it in for testing and replace if necessary.

If your meter is set to amps, it has to be inserted in SERIES in the circuit. In other words, remove a connection at a terminal in the circuit and connect one lead to the terminal and the other to the wire you just removed. If you're connecting to the contacts at the bulb socket, you're measuring the amps drawn by the meter by completing the circuit through the meter. Doing that can blow the fuse in the meter if the circuit is powered. (Don't ask how I know that. )

Are you actually draining the battery or are you just going by what your meter is telling you (connected incorrectly)?

no radio
I have the old generator still, need to update to alternator but the genny has been working well so I haven't replaced it.
no security system (most people I know don't know how to use a choke so I rely on that)
still have a few chewed up wires laying around, mostly under bed.
will get the battery load tested tomorrow.

3 days in a row of weak almost dead battery, charge in the morning and seems fine. Starts strong in afternoon but by morning is dead. if bat terminal is removed battery does not drain.
and ty for the heads up about the fuse lol will retest and post results

battery had no issues with draining or charging before, and I only reconnected the dome light wires. did not touch anything else .

I retested, this time with it in series lol not sure if I did it right (0.00 all the way across)? but not sure if it matters anymore. I feel dumb, It's only when I got down to unplug the wires below the fuse block that I saw a small chip of isolation missing from the back side of one of the orange wires, It was in turn making contact with the floor of the cab and grounding out. I didn't see it before but this time it threw a spark as I lifted the plug.

Shouldn't that blow a fuse though?

I suppose PO could have hard wired that spot in the fuse block, I have seen it before on some really methed up fuse blocks. will have to pull it off and make sure it's not to altered.

Glad you found the culprit.
It could have been a high resistance contact with the floor, acting like a light bulb and drawing little enough current not to blow the fuse.
Electrical Gremlins are tough to track down and kill.

Alright we can all take a deep breath now!

Yes, for a while I was thinking it was just haunted.

It is haunted with bad wire/wiring that needs redone.

it's getting closer all the time, just wish I had the $ to get it there a little quicker. as for now it gets me from a to b when I need it to.