Tail lighthelp needed

[Bagneaux]

My right tail light has no power at the plug that plugs into the tail light module. The turn signals, brake light and reverse light all work on that side. All other lights work on the left side except the license plate after I found the short and rewired the tail light. The yellow/black wire that goes into the plug goes to the left side and then into a really big wiring harness. The wiring diagram shows the left license plate light and the right tail light use the same yellow/black wire. I am very familiar with Fiats, having owned six, an 850 spider, two X1/9s, a Spider 2000 and two 124 Spiders, but I have little experience with electrical issues. What steps should I now take to get power to the tail light? I am hesitant to dive into that big wiring harness without guidance. Is splicing a power wire into the yellow/black wire at the plug a viable option? If so, where would a good source be?

[aj81spider]

I took a quick look at the 1978 wiring diagram. It's a simple (but sometimes hard given the routing of wiring) task to move down the connections to find where the break is. The wiring bundles themselves are almost never the problem - it's almost always connectors that have gone bad. The way I would approach this, based on the wiring diagram is as follows:

- The license plate light passes power to the tail light. The fact that your license plate light isn't lighting indicates it doesn't have power. I would check that at the connector to be sure. If you confirm it doesn't have power the wiring goes through a number of connectors.

- One of those connectors is the trunk light. Since you are back there already I would check to see if power is getting there. You're already in the trunk and it should be easy to find. If the trunk light has no power then ...

- The easiest next place to check is the fuse. I believe it is fuse 7 in your car. Check that there is power at the output of the fuse. This will bracket the problem as the wiring between the fuse and the license plate light.

- There is one connector between the fuse and the trunk light. I don't know where it is in the car, but unless you've cut a wire somewhere that is the remaining logical place for your problem.

Continuing to work down the diagram will eventually find where the power is being broken. I would not simply string another wire for a couple of reasons. First, if this circuit is interrupted and it's in a connector, then it's just a matter of time until other circuits in the connector go bad. Second, you are creating new electrical paths that may or may not be problematic, depending on where the break is and what else you are powering via that wire.

[18Fiatsandcounting]

One question for Bagneaux: How about the right rear side marker lamp? It should also be dead as it's on the same circuit as the right taillight and the left license plate light.

-Bryan

[Bagneaux]

Other lights on that circuit are working such as instrument lights and front left parking light and marker light. The right rear marker light is also off. There was a wire splice going to the license light so I was able to cut it out and add a spade connector for the existing female spade connector. BUT, still not on. I cannot find the trunk light so it was removed or hidden by PO. I do see a yellow/black wire loop in the opening right behind the left rear shock housing so I bet it was shoved up there and that is probably the problem. It is stuck in place and won't budge. I don't want to pull too hard. I will check this later today when my garage door is not in the direct sun. 95 degrees here today.

[18Fiatsandcounting]

Since the front marker lights are working, it does sound like the problem is a connection with that yellow/black wire for the right rear marker lights (taillight and side, and left license plate). It also sounds like the issue might be with the disconnected trunk light, and maybe a wire got disconnected that should be connected. I don't know where the trunk light is supposed to be on your model year, but on the earlier spiders, the switch for the trunk light runs off the left trunk lid hinge, and the light itself is up near the right rear shock absorber mount. Regardless of model year, the trunk light is hard to find, up under the sheet metal just behind where the convertible top mounts.

If you have a voltmeter, I'd start checking the voltage (with the parking lights turned on) on that yellow wire as it enters the trunk compartment and then the various places it goes. Sounds like somewhere there is a break.

-Bryan

[ORFORD2004]

Power to rear light goes from left side to right side. It's the big connector near the center on the left light assembly. Use test light to see if you have power at the connector both end.

[Bagneaux]

There is power at the connector for left tail light but not for right taillight not left license plate light.

[18Fiatsandcounting]

There is power at the connector for left tail light but not for right taillight not left license plate light.

Then it sounds like the "break" in your connection is occurring closer to the front of the car. Unfortunately, the only solution to that is to work your way back in the wiring to find where the issue is.

One thought: I know you said the fuse was OK, but try a different fuse for the right taillight/left license plate light circuit. Some fuses can look OK but actually be bad, or sometimes the fuse end connections are marginal.

-Bryan

[Bagneaux]

I pulled (with great force) out the trunk light wire and it was a bare spade connector touching metal, so that made the left license light work. Then I tried a jumper wire from left to right tail light and right one worked. I ran a new wire and spade connectors, and,voila, lights!

[18Fiatsandcounting]

Glad you were able to figure it out!