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No reverse lights


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Today at work I was flagged down by some kind people I work with and told me I have no reverse lights. I stopped by my dad's and asked him to look as I reversed. He also said I had neither left or right side. So this has me left here scratching my head. Would this be the NSS [Neutral Safety Switch] a fuse, or maybe somthing else? I don't know if any of you guys have had a issue with no reverse lights exclusively. I have tail lights. I have brake lights. I don't exactly know what I'm getting into here or if I need to be scavenging for a rare or unique part. The transmission is a AW4 Automatic transmission I6 4.0L engine. 

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I do not know what wire goes where and what does what. All the wires look dirty and one color from dirt. Is there a trick to taking the harness apart to clean it? Last thing I need to do is bust the harness and short something out. The harness I managed to find was near the rear of the truck that had I think 6 wires running into it. I couldn't see good since it was completely dark

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Crawl underneath the truck.  Locate the switch screwed into the trans.  With KOEO, use a test light to check for power getting to the switch (black/yellow). 

 

Put the trans into reverse.  Back probe the wire coming out (brown/white?).  Does the test light lite up? If not, replace the backup switch.

 

If you have power in, the check for power back. From the rear, locate the wire coming the back (brown/white).  It you have power at the rear, then check the light and the sockets

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Alright so here's my fuses. Here's the harness I speak of. I found my NSS on the passenger side of my transmission up towards the front. Where is the back up switch? I've had reverse lights before. I replaced a bulb one time early early 2022 or 2021. All of a sudden I don't have reverse lights. It's also dead of night here lol. Also there's my NSS. Managed to get myself in a spot to see it

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The last picture is the gear selector switch.  The rev. light wires run through that connector.  Unplug the connector and test power on the engine side of the connector.  It should be a Black/yellow wire, pin A.  (The wire is Yellow on the switch side.  )  Test for power on the engine side with KOEO.

 

Power runs back to the lights first through a White/Black on the switch wires then to a Brown/white on the engine side - pin E.

 

Keep working backward until you find where the power stops.

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Will do! Is the gear selector switch a common tail light no show? Truck cranks fine and goes into gear smooth. I do have a strong feeling this is indeed it since it's so oily and greasy in that area from oil and trans fluid over the course of almost 4 decades. Also what's the difference between a gear selector switch and NSS? Are they the same with different names or two totally different parts. Please excuse my lack of knowledge of this. Electrical stuff and switches of things like this are not my strong point. When I type "1988 jeep Comanche Gear selector switch" it gives the pictures and options for the NSS. Which sits up front of the passenger side transmission 

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I don't have an auto.  The 88 electric manual labels it the "Gear Selector" switch, but I think its the same as a NSS.  The TCU reads when the trans is in N or P.

 

Don't let the wiring scare you.  If you haven't downloaded the 88 electric manual, you should do so.  Print out the pages for the wiring you a researching.  Study it.  Get under the truck and examine the wires and connectors carefully before taking things apart.

 

In simple terms: electricity flows from a power source (Bat +) through wires and connectors, to a switch, to a load (like a light), then to a ground (Bat -).  The switch will either close the circuit - allowing electricity to flow to the load (light on) - or open a circuit - breaking the flow (light off).  When the trans is shifted in to reverse, the switch closes allowing electricity to flow to the lights.  That's why I have you test the electric at the connector feeding the switch.  If you have Bat + in to the switch, but not coming out of the switch when KOEO in reverse, then the switch is bad or just dirty from 40 yrs of dirt.  If power is coming out of the switch then the issue is further down the line.  Use the wiring diagram to assist with tracing the wires.

 

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Yeah I'll definitely troubleshoot that. I work 12 hour shifts from dusk till dark. It'll be cold for a while around here too. The bulbs I think are fine since I have replaced at least one of them in the last year or so. It more leads me to the NSS or a bad wire/bad harness thats at the back of the truck. I can "think" all i want and be wrong. Knowing is half the battle. So ill start with the bulbs first and see if I get anything with them. The harness I'm skeptical about taking apart because I can't tell what wire does what or goes where because they are all black/brown from crud. The NSS I'm hesitant to touch since I read that it's got a metal washer or like a connection patch and needs to pried off with care. I also don't have a way to read volts. But I so hope it's simply miraculously the bulbs burnt out simultaneously 

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If you end up having to look at the Underbody Tail Lamp Connector, these images may help.  

Unfortunately, I must offer the disclaimer that this is just my interpretation of the '88 electrical manual, and I haven't (and can't) confirm this on a vehicle.  My '91 uses a different connector.

Screen Shot 2023-02-03 at 10.27.51 PM.png

Screen Shot 2023-02-03 at 10.19.56 PM.png

MJ reverse light circuit 1G.jpg

MJ reverse light circuit 2G.jpg

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  • 2 weeks later...

Reverse lights fixed! I had my tailgate down and ran into it hard not paying attention when I was on my phone like a dork. Guess there was a loose connection. I was texting one of my buddies then BAM ran right into the side of the tailgate winding myself. I then got back in my truck to go get groceries. Ding ding ding! I now have them with the power of being clumsy!

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You should consider removing the driver's side taillamp and refreshing the ground wire/screw connection as a matter of course. To further improve that ground circuit, which is also for your fuel pump, do this:

 

IMPROVING THE FUEL PUMP GROUND

The fuel pump and fuel tank sending unit ground at a sheet metal screw up behind the spare tire on an XJ, XJ-Body-Ground.jpg?resize=300%2C162and behind the driver’s taillamp on an MJ.

Not only is a sheet metal screw a lousy way to ground things, this ground path is long and travels through some connectors that are prone to corrosion and moisture.

Locate the black wire on  the HARNESS side of the fuel pump/sender 3 wire connector. Remove a 6″ length of the split loom covering. Strip back about 1/2″ of insulation from the BLACK wire.1-fuel pump ground MJ

Take your new ground wire, preferably at least 14 gauge and 12 to 18 inches long as needed, strip it about 3/4″, and wrap it around the exposed part of the harness plug wire.1-fuel pump ground mj-002Solder the connection. Tape it up and reinstall the split loom covering.1-fuel pump ground mj-003

At the other end of your new ground wire, add a crimp on eyelet. Attach the eyelet under a bolt that goes directly into the chassis. Be sure to clean the attaching point til shiny and apply OxGard to the contact surfaces.1-fuel pump ground mj-004

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