HVAC Control Fuse

[H3 Hummer 64]

So I hook up a pair of 520s about a week ago. I tapped into the brown wire that goes into the 12 pin connector on the back of the HVAC controls for power to the switch. This was recomended by Fstop in another thread. Everything works great. Now I got the factory switch to replace the PIAA switch and when I hook that up it blows the fuse everytime. The fuse for the HVAC controls is only a 10 amp fuse. If I put the PIAA switch back on it works fine. So how do I fix this? Can I put a larger fuse in its place? Do I have to find another 12 volt power source? Please help.

[f5fstop]

DO not put in a larger fuse, the wiring is not capable of more current.
Can you explain the differences in connection between the two switches. Does the PIAA have a LED light? Then again, a LED draws such little power it should not matter.
Possibly, the factory switch is bad.
Hard to say without knowing exactly how you wired the system.
If you can, make up a hand wiring diagram of what you did, and scan it and send it to me at f5fstop@comcast.net. I would be curious.

[H3 Hummer 64]

Ok I'll working on scanning a diagram. Its actually installed how the PIAA instructions show. I'll explain it to you for the time being. From the relay there is a direct main power wire to the battery, a ground to the battery, the wires to the lights, the relay ground (grounded to the chassy), and the wires that run to the switch (power, ACC, ground). I spliced into the Brown wire going to the gray 12 connector that plugs into the HVAC controls behind the selector/rear defroster knob for power. The Piaa switch has a small LED that is lit green what the lights are off and red with the lights are on. The factory switch has the one orange light that lights up with the lights are one. The wires off the factory harness were not labeled except for A, B, C. But after testing them I found A is power, B is ACC, and C is ground. All I did was cut off the Piaa switch and hook in the factory one. The lights will come on for a split second and the switch will light up then the fuse blows. I believe its #59 a 10 amp fuse in the box. I just cant see how the factory switch could draw that much more power. One other thing I noticed but I dont think should make a difference is that the wires from the factory switch are much thicker than the Piaa wires. I hope this helps. Thanks for taking the time to figure this out. Also once I put the Piaa switch back on it works fine. Even turn on the rear defroster which lights up on the knob and all is fine.

[f5fstop]

Not sure which Pin A you tapped into, but you should have probably tapped into Pin K, which is Ign 3 voltage.
However, the problem is probably with the different types of switches. I will assume PIAA has the same type of switch as KC.
12 Volts into the switch, inside the switch 12 volts goes to the green LED. When the switch is pressed, 12 volts to the green LED is removed, and 12 volts to a RED LED is applied, as well as 12 volts through the switch to terminal 86 of the relay, which energizes the relay and allows full B+ from pin 30 to the lights on pin 87.

The factory switch is designed differently. B+ is applied to both pins A &C of the switch. When the switch is pressed power is sent to ground. Pin A will light the LED, Pin C supplies the ground path for the relay, allowing the relay to close supplying power from pin 30 to pin 87 and to the lights.

In other words, the factory switch is operating the ground side of the relay's coil, while the PIAA switch is probably operating the hot side of the relay's coil (supplying power).

When installing a factory switch with the KC lights, I could not use the same wiring diagram supplied with the KC lights. I had to do some splicing and reverse the relay pins.

Easy fix, with some small changes. If you send me the schematic, I'll mark it up and send it back.

[H3 Hummer 64]

Ok F5, I've sent you an email to your comcast account. I included a PDF of the schematics. Thanks for taking the time to look at this for me.

[f5fstop]

Did you ever get the reply, and get the switch rewired?

[H3 Hummer 64]

I just got to look at your email today. I'm on a Mac at home so I need my computer at work which has Microsoft to open your emails. I'm not sure if Im going to attempt it or not. I have to look at it a little closer but might to a little too difficult for me. Either way that was awesome that you took the time to do that. Thank you. Ill let you know if i try it and the out come.