Riddle me this one, Batman...

[Mark Rinker]

Truck (#4, below) and empty trailer, everything normal at 25mph residential street speeds, truck dies and the horn comes on, nonstop!

Coast to the curb. Turn ignition from ON to OFF, horn stops. Turn back to ON, horn blares. Shut OFF, pop hood, pull horn fuse and then attempt to reSTART...

Now everything shuts down, including dash indicators and no crank at all.

I know batteries/connections are good and soon find that a 40 amp IGNITION mega-fuse is blown. Upon each attempt to replace and restart, the same fuse blows instantly when you hit START. After three $2.00 fuses, I give up.

Truck is towed to local shop (not GM dealer) where they scratch their heads until I stop in and chat with the owner/head mechanic and sort things out this morning. Interestingly - it decides to start and run fine (multiple times) when I am there! We cycled and wiggled the key and ingition switch to death, and agree there is no problem there.

Guesses? I have developed a strong theory and am waiting for the part to come in to test it out. I hesitate to head out across country - as I am convinced this will reoccur at some point, stranding me with loaded trailer next to the interstate with horn blaring and no start!!!

Clues: The truck had been off the trailer and making some VERY high power passes with extra diesel and propane stacked, only 15 minutes or so before all this occured. (When the truck died, all stock programming was back in place, and propane system was OFF.)

Well, Batman - whats your guess?

[JohnC]

Holy theft deterent, Batman!

[Mark Rinker]

No kidding! I am glad it happened near home rather than 300 miles away.

BTW - there is NO aftermarket security system on this truck, and it does NOT appear to be factory security system related - at this point... :)

[More Power]

The 40-amp IGN A fuse passes power through the starter relay to the starter when the ignition key is rotated to the start position, and it passes power through one set of contacts in the ignition sw. From the ign switch, power is distributed to IGN 1 fuse (10-amp), TURN fuse (20-amp), SEO IGN fuse (15-amp), and the AIR BAG fuse (15-amp).

I'd look first for a starter problem if the fuse only blows when you attempt to start the engine. Pull the starter relay to test.

Jim

[TAD]

I don't know if it applies but my wife had an 02 Buick Rendevous that did the same thing. The horn would just start blowing and had to pull fuse under hood to stop it. Then the lights would not shut off and would run the battery down. Just before it started the dash gauges would shut -off and then reset as if you turned the key off but the car would continue down the highway without even a hiccup.
The dealer ended up replacing the Body Control Module (?) and that fixed it.
TAD.

[Quack_Addict]

a 40 amp IGNITION mega-fuse is blown... After three $2.00 fuses, I give up...

Try a $2.20 50 amp mega-fuse. If problem persists, try $2.50 60 amper. :)

Honestly, it's an interesting problem. There is some hand-shaking that goes on between the PCM and the BCM that allows the engine to run but nothing that I can think of that would cause a 40A mega to keep blowing.

As the truck is modified, did whoever performed the work tap into the ignition circuit somewhere for some reason? Maybe the 'VERY high power' passes shook something loose and it's arcing out on the starter terminal or other?

How does the alternator gauge look with the engine running (steady gauge at ~14-15V)? I had a voltage regulator go out one time and alternator went "full field" frying a fusible link to the starter (amoung other things)... but that was on my `82 K5...

[SoTxPollock]

I'd advise against trying higher AMP fuses. That fuse or fusible link is designed to fail before you burn up a much more expensive item, whereever the problem might be. Somethings shorting to ground somewhere.

[Mark Rinker]

We are replacing the entire starter and starter solenoid with a takeoff unit from Ebay...only $79 and shipping.

Stealership wanted $800...

I'll let you know what happens. I think we fried the starter solenoid from high downtube temps when 'experimenting' with big fuel stacks. The new one will be heat shielded with tiles from the underside of the space shuttle - or maybe just some shiny stuff from NAPA...

[Mark Rinker]

The new starter appears to have solved the problem. :)