I have a '99 Ranger 3.0 ext. cab. I have no dome light or cargo light when I move the light dimmer up past the detent. When I open the doors they do not trigger the dome light, but they do trigger the "door ajar" light on the dash, and the drivers door triggers the dingger if the key is in the ignition. Does this sound familiar to anyone? Does anyone know how to check the GEM module for proper operation?

 

Sounds to me like a blown fuse. Look for a diagram of fuse locations and start there.

 

Darn, I checked the fuse at the start of the struggle and forgot to mention it. The fuse was hot on both sides, and I removed it and reinstalled it in case the contacts had deteriorated, but it felt good going in. I also checked all three fuses for the GEM in case it is involved, and they are all good and hot both sides with the switch on. Thanks for reminding me to complete my previous post.

 

The next step I would suggest is scooping up a wiring diagram book for your truck and following the circuit path for the lights. Here's a dumb question though, could the bulbs be burnt out?

 

The main bulb on the dome light is good. Today I checked on the cargo light, thinking it should be simpler than the dome light. Both bulbs were good and I back probed the connector and found no voltage with the dimmer switch rotated to on. The third brake light uses the same ground wire and it works so I guess the ground is good. I found a wiring diagram that shows a wire from the light switch to the dome light, but no cargo light, so I wonder if it is correct. It does show the door switches coming from the light switch and connecting to the dome light wire. I should check the door latch switch feed from the light switch for voltage, but I am a bit old for crawling upside down under the dash. Since all the important lights work, I might leave good enough alone. Thanks for your input.

 

I remember sitting upside down in the drivers seat a couple times when I tied into my turn signal wires when I added my signal mirrors. They weren't fun. Try pulling the headlight switch out and probing that connector maybe? It wouldn't involve standing on your head.

 

Today, on line, I found someone with a '99 B 4000 with the same inoperative dome and cargo light. He fixed it by replacing a relay in an under dash relay box to the right of the steering column. I found a stylised drawing of a '99 ranger dash showing a relay box containing a battery saver and gear shifting relay. Is anyone familiar with this relay box? It looks like I can reach it by removing the radio and center instrument cluster.

 

Well, there is no relay box under the dash of my 99 ranger. The Ford pickup must be a bit different from the Mazda version. I thought the problem relay might be in the under hood box so I swapped them around but it did not fix the dome/cargo problem. Perhaps the problem is in the GEM. I'm not willing to buy a module so I will just live with the problem. Thanks for the encouragement.

 

That sucks. It does sound like it could be a GEM issue at this point, since everything is routed through it. I'm glad my '05 has a SJB (smart junction box) instead of the GEM. Its all fuses and relays for the body controls

 

You can get to that relay box by looking at the top of the gas pedal to the right. It will have a black cover on it, contains several relays. One of them is for interior lighting.

 

Thanks, I have seen a picture of it and know where it should be, but that space is empty on my truck.

 

Well, today everything started working, for no apparent reason. The dome light works when opening either door, and the cargo lights work with the dash dimmer switch. I have not worked on the truck for at least a week. Strange.