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Regarding 79 K5 Dome light Wiring

L

ladybugblazer

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Howdy folks.

So I decided to start digging and finding out why my dome light wasn't working today. I took off the cover and found found that both the leads were hanging only with a few strands of wire and bundles of electric tape. After taking off the electric tape to see what was under I was greeted with the attached image. Not sure why there are 3 wires I labelled them 1, 2, and 3 in the picture. Two are yellow (1 & 2) and one is red (3). The two that are yellow (1 & 2) seem to be going to the back of the truck, and the one that is red (3) seems to be coming from under the headliner towards the front of the truck. Wires 2 & 3 get combined on one of the leads. Could it be possibly that this is to continue power to the back lights?

My plan was to cut off the two bad leads and crimp/heat shrink in two new ones that I already bought, but because there are three wires I need to figure out how to connect those 3. I don't wanna solder. I found this WAGO Connector of amazon and was thinking about using this:
https://www.amazon.com/Wago-221-413-...dp/B06XGYXVXR/
But I was just wondering if this is a good fix or if I am even doing this job right because I'm looking at the wiring diagram and I see that there are supposed to be two splits from each lead to go to the back and with this setup I'm not sure whats going on.

Thanks,

-Ladybug

IMG_2711.jpg
 
The orange (#3) should be constant "hot" going to the light, the white wires are switched ground from your door switch and headlight switch. A good quality crimp "butt" connector and some heat shrink should patch that mess up just fine. I prefer the crimp fittings that are heat shrink...
 
Yes the orange wires are battery hot for the courtesy lights and cigar lighter. To me I see the 2 "yellow" wires appear to be dirty white 1, and faded orange 2. The red wire 3 seems to be an add on for battery hot power.
Wire #2 should have battery voltage at all times, it has a fuse in the fuse box, courtesy fuse. Wire 1 is a switched ground, the door jam and headlamp switch all wired in parallel. Check wire 2 for battery voltage, and ohm check the white to ground ( after making sure there is no power on wire 1)

Welcome to CK5 @ladybugblazer
 
Thank you guys this is all good information. Wes, should the battery be disconnected before testing the wires for voltage/ohm? Also what values should I be getting for this two procedures?

Thanks
 
Thank you all this is all real good information.
Wes Harden said:
Yes the orange wires are battery hot for the courtesy lights and cigar lighter. To me I see the 2 "yellow" wires appear to be dirty white 1, and faded orange 2. The red wire 3 seems to be an add on for battery hot power.
Wire #2 should have battery voltage at all times, it has a fuse in the fuse box, courtesy fuse. Wire 1 is a switched ground, the door jam and headlamp switch all wired in parallel. Check wire 2 for battery voltage, and ohm check the white to ground ( after making sure there is no power on wire 1)

Welcome to CK5 @ladybugblazer
Click to expand...
Wes, should the battery be disconnected when testing the wires for voltage/ohms? Also what values should I be getting

Thanks
 
To test for voltage you'll want the battery connected. You never want to ohm check a circuit with live voltage on it, doing so will blow a fuse or damage your meter.
So battery is better disconnected for ohm checks.
You can and should check any circuit for voltage before you you use the ohm setting.
 
Wes Harden said:
To test for voltage you'll want the battery connected. You never want to ohm check a circuit with live voltage on it, doing so will blow a fuse or damage your meter.
So battery is better disconnected for ohm checks.
You can and should check any circuit for voltage before you you use the ohm setting.
Click to expand...
Alright Wes thanks for clearing that up for me. I'm getting around 12.2-12.4 volts from the end of that Wire #2 that has #3 spliced into it. For Wire #1 I'm getting around 2 volts for some reason should I still Ohm check it?
 
My blazer also has a dome light in the hard top behind this one. This one doesn't work either and has only 2 wires the white one and then and orange striped/white one. Not sure if they are the same as the 2 that I've been testing though seems no red #3 wire here.
 
My current suspicion is the added red wire's load caused a heavy draw, and might be some melted insolation mid loom allowing a short between orange and white.
Disconnect the battery and ohm check both wires to ground and the 2 wires to ea other. Remove any bulb in the other lamp. Remove cigar lighter or USB adapter, and inspect socket for debris.
 
Last edited:
Wes Harden said:
My current suspicion is the added red wire's load caused a heavy draw, and might be some melted insolation mid loom allowing a short between orange and white.
Disconnect the battery and ohm check both wires to ground and the 2 wires to ea other. Remove any bulb in the other lamp. Remove cigar lighter or USB adapter, and inspect socket for debris.
Click to expand...
Alright Wes I separated all the wires out so I just have white 1, orange 2, and red 3. I tested each wire on eachother and each on ground, The only test that got a reading was the orange wire #2 to ground and it was around 11 ohms. This was the only wire that got continuity and it was to ground. I don't have a cigar lighter and all I have there is a connector with a single orange wire on it (see attached picture).

IMG_2712.jpg
 
hmm strange wire #2 was the wire I would have thought to be battery hot. There might be another lamp under the dash completing the path to ground, if so remove that bulb. Twist the headlamp switch knob to middle of rotation, just to make sure dome lamp is not switched on.
Also check the #1 to ground with either door open or both, giving the door switch plunger a little twist can help get better contact.
 
Alright I've attached a new picture of the setup I've been testing with. I pulled out a light bulb under the dash and now #2 shows around 300 kilo ohms of resistance and doesn't beep for continuity anymore. #1 also I tried getting a reading for it but still nothing and I was pressing against the door switch plunger with my toes and set the headlamp switch in the middle.

IMG_2713.jpg
 
the switch door should be in the out position, to close the circuit to ground. I like the ohm reading on #2 much better.
 
Regarding you pressing the door switch plunger with your toes, that is a "normally closed" switch which means it turns the light on when it's not pressed. Pressing it will open the switch and cut power.

A very common failure on these switches is that they will be stuck open regardless of the plunger position. I'm not saying it's your issue, but you definitely should pull the switch and check it with a meter. Every old GM I bought has had bad door switches (stuck open).
 
Sorry to further clarify I tested the switch with it both closed and open. I believe the switch is fine because that same light that I removed under the dash would light up with the door open and turn off when the door was closed. However I do have one question if I rotate the headlamp switch knob should the light under the dash turn on too with door closed? Because it would not
 
ladybugblazer said:
However I do have one question if I rotate the headlamp switch knob should the light under the dash turn on too with door closed? Because it would not
Click to expand...

Mine does, but mines got at least a slightly newer wiring harness. I doubt this would have changed.
 
Yes I believe it should, not turning on with the switch is/could be a second issue.
I forget what year is this Blazer ?
 
Looking at a 77 wiring diagram the ground goes to the under dash lamp 1st, then on to the roof dome lamp, it appears there is an open between the 2.
 
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