Horn fuse keeps blowing.

[thelincolnguy]

Hello all. A friend has an 87 k10. It has the factory cigarette lighter. It is wired from factory with the horn circut on constant power. He had no power to the lighter or the horn. Replaced fuse and blew the horn once and fuse was gone again. Removed the cig lighter outlet and replaced the fuse again. Blew the horn, no problem. He picked up a cig outlet and installed today and continues to have the problem. Cig outlet power wire has constant power on test light when cig port is disconnected and horn blows fine. It is self grounding

[82silverado]

There is a direct short in that circuit somewhere.

[hatzie]

If I read your prose correctly.  The fuse doesn't blow out til he plugs in the HOT lead on the lighter power socket.

Some of the el-cheapo lighter sockets come pre-shorted. 

[thelincolnguy]

Yes it was doing that on both the old and new socket

[hatzie]

Take the lighter socket back.  I'd test the replacement in the parts store with a meter.  If it ohms out shorted between the body and the tip don't accept it.

[bd]

Is the lighter element installed or is the socket empty?

[Irish_Alley]

got a question, whats he lighter have to do with the horn. besides on the same circuit. could he be attaching the wire to the wrong location on the cig lighter? (i.e. the ground)

[hatzie]

got a question, whats he lighter have to do with the horn. besides on the same circuit. could he be attaching the wire to the wrong location on the cig lighter? (i.e. the ground)

That's a good point. 
What's obvious to You and I may not be obvious to everyone.
The HOT terminal is the centre of the lighter socket.  Ground is on the body of the socket.  I've forgotten whether GM even bothered to use a ground wire or just depended on the metal structure of the dash.
In this picture the HOT or + terminal is a machined round Male Bullet pin in the centre of the base.
The semi-optional, 1/4" disconnect, ground connection is welded to the sleeve.

[bd]

It wouldn't be the first time someone inadvertently connected B+ to the spade terminal on the shield.  Many of the production lighter sockets used a spade center terminal.  With limited access and poor visibility, it isn't difficult to make that mistake.  Generally, GM grounded the lighter through the ashtray hinges and surrounding sheetmetal - there was no dedicated ground wire.

[thelincolnguy]

Thank you everyone for your replies, we determined that the issue was a bad factory socket, and 3 bad sockets at the parts store in a row. Finally went to napa and bought a quality part.