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post #1 of 3 Old Oct 15th, 2011, 9:30 pm Thread Starter
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The mystery of my PIAA system solved

The mysterious behavior of my PIAA fog lights has finally been solved!

A few days ago, armed with a new light switch and a new relay, I rewired my fog lights. It didn’t solve any of the mysterious behavior of my system.

I could only get my PIAA fog lights to work by using the plus line on my turn signal as the source for the PIAA switch. No other voltage source worked. Plus, the LED just would not work in the new switch.

This simple DC circuit has kicked my ass after many hours of trying everything I could think of.

Once again, I verified that the PIAA switch LEDs light up when I ran 12V directly to the switch. I verified that the relay was closing when I connected it directly to the PIAA switch.

When I put everything back into the wiring harness, the LEDs lit up, the relay clicked when I hit the switch. But, the fog lights would not come on.

Once again, the PIAA fog lights beat me. The score was PIAAs 3, zero for me.

I remembered what this fellow from VT told me one time: “When all else fails, check the fuse.”

Yup. The fuse was blown. I let out a bid sigh of relief—I had extra fuses. So, all I needed to do was replace the fuse and I’d have beaten my PIAA lights!!

When I inserted a new fuse into the fuse holder it sparked?! Course, it shouldn’t spark with the switch off.

Puzzled, I reattempted to put the fuse in the holder watching the sparks fly as I did. Yup, the fuse blew!?

When I ran the pair of wires to the fog lights, I used a pair of wires with a fuse holder near the connections to the battery. The line was a pair of black wires, like speaker wire, but heavier. Just like speaker wire, one wire had white printing on it.

I checked the direct run from the battery into the nose cone. When I check for continuity between the ground wire from the battery to ground in the harness, it was an open circuit?

The plus line from the battery, with out a fuse in it, showed continuity to ground!!

When I wired up the direct run to the fog lights I had run the ground wire of the wiring harness to the plus wire from my battery. And, the negative wire from the harness was connected to the plus terminal on the battery.

Since the wiring harness to the battery was a closed system, it worked when connected to the turn signal. Course, since the plus voltage was running thru the ground wire on the switch, the LED would not work. The switch worked, but not the LED.

Once I got the home-run from the battery connected correctly I was able to use a switched wire from the map light as the trigger for the switch instead of a wire connected to the turn signal.

The Led lights up for when the lights are on, and the fog lights work.

Mystery over!

Best from Gorham ME

"He was a foul caricature of himself, a man with no soul, no inner convictions, with the integrity of a hyena, and the style of a poison toad." H. S. Thompson
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post #2 of 3 Old Oct 17th, 2011, 7:50 pm
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Re: The mystery of my PIAA system solved

Not sure I'd publicly admit to an accidental wire swap on this simple job but 3 points for doing so!

Actually, I think many of us know how easy it is to make this kind of an error in bad visibility in the shop or when one is in a hurry. That's why I'm in the habit of testing everything I do as I do it. What I really want to avoid is accidentally frying all or part of a wiring harness and what fuses can do as protection may be limited if the circuit is wrong.

Generally I wire with standard colors (eg black grounds and red pos) or sometimes factory colors (BMWs brown ground) if I've got them in inventory in the right gauge (I've got a fair amount of different wire). Helps prevent stuff like that. I never use any of the speaker wire or similar but I will sometimes use various types of outdoor cable instrument or comm wire especially where the sheathing may help keep random RF crap out of something where it might matter. Most industrial plants generate a lot of this kind of stuff as scrap and a few bits go a long way on the bike though almost all is 20 gauge or less so is for low currents only. I use a lot of shrink wrap, loom, and cable ties and solder almost everything- except the rare use of a posi-lock. I avoid spades (except when making relay sockets, etc) where possible - only weatherpacks, deutsch or similar, also. I don't get failures in service but it does take me a bit longer to do most jobs. The connectors I use allow disconnectingl for service easily when needed without cutting any wires.

Last edited by racer7; Oct 17th, 2011 at 8:34 pm.
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post #3 of 3 Old Oct 19th, 2011, 10:35 pm Thread Starter
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Re: The mystery of my PIAA system solved

One of the hazards of working on my LT in the early AM using coffee to stay awake in a dust filled garage--I'm allergic to dust. dust is a part of life in Tucson.

best Bob

"He was a foul caricature of himself, a man with no soul, no inner convictions, with the integrity of a hyena, and the style of a poison toad." H. S. Thompson
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