Weird bulbs

[rodo]

And... I removed the dimmer. I connected the two wires with a 10v fuse. Battery connected: Blew instantly. Hm, okay. So I used a 15v fuse. Blew the fuse in the fusebox. Replaced that fuse and I'm back to where I started but, now, I know I'm shorting somewhere. It all worked before I installed it...

[Akspider]

Agree with spider2081 - if you have the connection to the cigar lighter bulb jumped that will tie +12 to ground and definitely will blow a fuse. Maybe check your marker lights if they're out fuse 8 could be blown. No problem jumping across the lamp dimmer to bypass that - just won't be able to dim the dash lights. Good luck

[spider2081]

I connected the two wires with a 10v fuse.

Fuses are in a car to protect the cars wiring from overheating and causing additional problems like electrical fire. One should never put a larger fuse in a circuit than the circuit is designed for. Fiat designed the circuit for a 8 amp fuse. troubleshooting a portion of that circuit one should use a fuse smaller than 8 amps. A 2 to 5 amp fuse would be a better choice.
Yes there is a short after the dimmer control if you are blowing fuses when you connect the dimmer wires together with a fuse. You didn't mention removing the wire you installed in place of the cigar lighter bulb. Was it removed for your tests??
The Dimmer's internal fuse is most likely blown, before that is addressed you need to get the lights to work by locating the short to ground and correcting it.

[rodo]

Okay, I got something messed up: all this time I thought I was discussing the lighter lamp. No, it is...something else. My lighter lamp is still wired in; I actually read the schematic this time instead of assuming. I have NOT rewired the lighter lamp. This "other thing" plugs one end into the ground pod near the ignition and the other into the back of the lamp for the fibre optics. So it is a ground. That is the one I "jumped". I wrote it like that as this wire isn't just a plain wire. both ends go to a..sort of black rubber cap. Inside it was a tiny light bulb. Looks like the cap slides over something. Bulb is gone. I just ran a wire from fibre optics bulb to the ground pod. (But what the heck is that tiny bulb for, what does it illuminate...in a tiny way?)

So that does not seem to be the issue. Now I'm popping the fuse in the panel when I jump the dimmer. I get that. My guess is that one or more of the wires that go to gauge lamps is shorting, somewhere. At least it is a relatively contained part, only the gauge lights.

Could be worse.

Thanks for the continuing help, everyone.

[spider2081]

This "other thing" plugs one end into the ground pod near the ignition and the other into the back of the lamp for the fibre optics.

OK so does this mean you have not removed the connection to ground that you installed ?? No matter how convinced you are that it is not part of the issue it may be the last thing that changed before the fuses started to blow. You have the wire diagram can you find the wires you are dealing with on the diagram ?

I have an 80 Spider I just checked (visually/physically) its Fiber optic lamp connection. The power to the lamp socket is a single push on spade terminal. It has 2 white/red wires in the spade. One is the power from the dimmer and the other continues on bringing power to the other dash instrument back lighting. There is no ground wire for many lights in Fiat Spiders. The light sockets are grounded to the chassis by the way they are physically mounted. The fiber optic socket is grounded to the chassis so there is no ground wire needed for it to function. Maybe a previous owner added the wire you are talking about for some additional lighting.

[rodo]

Good thought. I'll give it a try. I also noticed today that the female part for the fibre optics, the part that is screwed to the metal, is a bit loose. Off to the garage.

[rodo]

BAM. So, the saga... removed the unnecessary ground and tried it. Nope. On a whim, removed the dimmer and did the jumper. Yep. Lights on. Okay, so bad dimmer. Put my spare on. Nope. Two bum dimmers. Figures. Already taken one of them apart. Fuse in the dimmer somewhere? Anyone else repaired one?

Thanks for all the advice. Another step done.

Now...just need to call my therapist and warn him that I'm attempting to reinstall the gauge cluster and attach the (hard to find, hard to reach) odometer reset knob.

[18Fiatsandcounting]

Okay, so bad dimmer. Put my spare on. Nope. Two bum dimmers.

I seem to recall that two bum dimmers are known as a bummer....

But seriously, you can take the dimmer apart, at least on the models I've had. There should be 3 tangs on the back that you can very carefully bend to pull it apart. Don't bend the tangs any more than you absolutely have to because they tend to break. Carefully pull apart the switch, and watch for the spring loaded contacts that will try to shoot off into the dark recesses of your garage if you disassemble too fast. Clean it up, lubricate, put it back together, and maybe it will work.

-Bryan

[spider2081]

If you know how solder electrical connections the dimmer can be repaired. Originally i took them apart and soldered a single strand of 19 strand #16 wire in place of the blown fuse. Now I don't take the dimmer apart. I connect an external in line fuse holder and use a 2 amp fuse. Here is the process.

looking at the back of the dimmer rotate it until the 2 terminals that the cars wires were on are facing 12 o'clock. the one closest to the center will be facing 3-9 o'clock. at the bottom of the black are 2 brass tabs that stick out of the bakelite about 1/16 of an inch. Clean then with with a file or Dremel wire brush. Apply electrical solder flux paste to them. Heat with solder iron and the tin with electrical solder. Take 2 lengths of #22 wire strip about 3/8 inch of insulation off one end of each. Heat the bare wire and apply solder to the wires . Reheat the terminal on the dimmer and solder one wire on each of the terminals. Splice the inline fuse holder to these wires. Plug in and test. Or you can test with an Ohm meter be connecting it to the 2 wire terminals. I don't remember the value range but I think its something like 1/2 to 10 ohms as you rotate the knob.
Secure the fuse holder where it can be accessed for fuse replacement in the future.

[rodo]

Okay, first of all, great joke about "Bummers".

thanks for the directions on how to patch the dimmer. I'll add it to the list.

[18Fiatsandcounting]

This is just some extra information. I happened to be sorting through my box of spare electrical odds and ends yesterday, and I found two extra dimmer switches. Given the discussion on this thread, and since the measured resistance across the two terminals as I turned the knob was very erratic on both, I took them apart. What was interesting is that one of the dimmers had that little internal "fuse" wire between the two halves of the inner assembly, and the other didn't. So I guess some model years had that internal fuse and some didn't. I don't know what model years my two spare dimmers are from, but they are probably pre-1978.

The good news is that they both cleaned up fairly well and now sweep from about 5 ohms at one end to close to 0 ohms at the other, with an open circuit when the switch is "clicked" all the way counterclockwise.

-Bryan

[RRoller123]

That is really useful info! I just jumpered across mine, so it is permanently at 0 ohms.

[18Fiatsandcounting]

Thanks, and I also did some quick mental calculations on the heat (watts) in the dimmer switch. I seem to recall that the type of bulbs used in the instrument cluster are about 0.3 amps each, so if you have 10 bulbs between the instrument cluster and the other illuminating lights, that would be about 3 amps. Watts = current squared times resistance, so that would be 9 times 5 ohms, or 45 watts, when the dimmer is set to low. Assuming the bulbs still draw 0.3 amps each when turned down, which they might not.

45 watts in a small enclosed space is significant, so you can see why the dimmer switch has holes in the side to dissipate heat. And beefy contacts inside.

-Bryan