why not to interrupt an ignition wire

Copied from a GM TSB. Though they mention ignition interrupts, the same would apply to fuel pump wires. Stick with the starter wire like the manual says to do.

Accessories - DTC's P0300, P1380, P1381

Bulletin No.: 02-06-05-004b

Date: February 14, 2006

INFORMATION

Subject:

Misfire DTCs P0300, P1380, P1381 and catalytic converter Damage Due to Installation of Alarm Systems

Models:

2006 and Prior GM Passenger Cars and Light Duty Trucks2006 and Prior HUMMER H2, H32006 and Prior Isuzu Light Duty Trucks

Supercede:

This bulletin is being revised to add model years. Please discard Corporate Bulletin Number 02-06-05-004A (Section 06 - Engine/Propulsion System). General Motors Engineering, in an effort to determine the root cause of catalytic converter damage, has determined that aftermarket alarm systems incorrectly installed in vehicles have the potential to cause misfire codes and damage to the converter. These alarm systems use a circuit interrupt which utilizes the ignition circuit on the vehicles.

These alarm systems utilize mechanical relays and normal vehicle movement can trigger these relays to engage and disengage the ignition circuit while the vehicle is in motion. These disruptions of the ignition circuit, which occur in milliseconds, may cause more fuel to be commanded. Overtime, this dumping of fuel on and off again can cause misfire codes and ultimately damage the converter assembly.

Important: Engineering could not identify any alarms that utilize solid state circuitry that would eliminate this concern. Because of this, it has been determined that all alarm systems must be routed through the starter circuit in order to avoid this condition.

Dealers must be aware of this issue and take note of the wiring on vehicles with alarm systems that come in for repair, particularly for catalytic converter damage that seem to have no known root cause.< language=>

C Renner's Auto Electronix

My service is cheap, quick, and good - pick any two

Sounds like a bunch of "technicians" that can find the real problems with their vehicles..... :)Kevin Pierson

Also, it should be noted that if a starter kill setup fails, it's safer. Faled Starter Kill You're stranded at home or at the mall. It's an annoyance, but the worst you'll need is a tow. If the starter kill should somehow fail while the car's going down the road, it doesn't matter, because the car's already running. Failed Ignition Kill The car can die while driving. At the least, you're stranded in an inconvenient place. Even worse, you could be stranded in a dangerous neighborhood, or at the side of a highway, where you're likely to get hit. Even worse than that, if the car dies when you're in heavy traffic, it might come to a stop before you can coast over to the breakdown lane, leading to a serious collision.

Yes Chris Luongo is correct, as far as installers are concerned its more of a saftey issue, I remember back in the day we would ground the neg going to the coil with a toggle switch.

opps..i meant to say ground the pos going to the coil..

Ah, I think I remember that too. My father had a brand new '82 Accord, and the dealer installed a Chapman hood lock and starter kill, the kind with the cylindrical key. The "technician" at the dealership who installed the system draped the coil-kill wire right atop the engine. It didn't take long for the wire to melt through, leaving my father stuck on Boston's Tobin Bridge. He found the problem himself, ripped away the burned wire, and luckily, the car started again. Later he commented on how the car, with all its thousands of parts, made its way out of the Honda factory perfect and clean, until they started adding stuff to it......I have to admit he was right.