Let me say thank you in advance to everyone here. I've gotten a lot of good advice and troubleshooting steps from this forum. Next, my Jeep is a 1998 cherokee sport 4.0L.

Initially started out with realizing the backup lights weren't working. Started with the simple stuff. Checked the fuses and bulbs. Then I read about the neutral safety switch. There was an issue there, wouldn't start in neutral. Took it off, cleaned all of the contacts, lubricated it, and tested all of the positions for continuity. No issues. Put it back on, properly aligned it. Starts in park and neutral. Put it in reverse, no lights.

Next, I removed the tail light assembly, and checked the voltage between the contacts = motor off 3.9v, running 11.9v. Also checked between the contacts to the vehicle body = motor off 3.9v, running 12.1v. Bulbs are visually good and have continuity. I'm at a loss, any help would be greatly appreciated.

 

Check for resistance in the sockets, If it's above 5 ohms something's wrong. Also make sure both bulbs have a good connection when in the sockets.

 

Alright, I'll look into tomorrow evening after I'm off duty. I'll let you know what I find out. Thanks.

 

What exactly were you measuring? There should be no voltage at the sockets unless a light was turned on.

 

Alright, round 2. I checked the resistance in the sockets with my multimeter set at 200 on the ohms setting. The following is what I got.

Everything off in the vehicle:
Between contacts- both 1.1 ohms
Between each contact and the body- all four 1.1 ohms

Key in the ignition(just before starting the motor), in reverse:
Between contacts- left .5 ohms, right .3 ohms
Between each contact and the body- left .3 ohms, right .1 ohms

Cleaned the contacts with a fingernail file and electrical contact cleaner, made sure the contacts were pushed forward enough they would actually touch the bulbs, and swapped the brake lights and backup lights to ensure the bulbs were good (they are matching bulbs). Swapped bulbs worked on the brakes but not on the backup lights. So, still nothing.

 

I was measuring the voltage between the socket contacts, and between the vehicle body and the contacts. With the engine running and set in reverse with the emergency brake set.

 

Not necessary to have the engine running. Key "ON", shifter in "R", parking brake "ON", should suffice. So the reverse lamps have never worked? With 12V and a good ground they should.

 

No they've never worked. I bought it late 2011. Then deployed a couple of weeks later. Been getting it back to standard since I returned home. I'm only getting 3.9 volts with the engine off, 11.9 and 12.1 running.

 

I would go ahead and replace both bulbs then, see if that helps.

 

Alright, sorry for the delay in getting back with you all. Anyway, I borrowed a friends multimeter (one of the more expensive ones that automatically selects range), and I was only getting 2.5 volts at the socket. I don't know if something is loose somewhere else or I simply wasn't paying attention and set mine to the wrong range. Either way not enough volts. So I checked the voltage at the NSS harness, getting 2.6 volts.

Started tracing wires from there. The wire that delivers voltage to that circuit ties together with the a/c clutch control relay and the cooling fan relay. I can't say I've figured that one out yet. Got a lot more wire tracing to do. I came up with a temporary solution. I ran and splice a new wire with an in-line 20 amp fuse until I can get the whole wiring harness torn apart. Also, the contacts at the sockets weren't touching the bulbs, added some solder to the contacts and solved that problem.