Intermittant Electrical death-maybe ignition Switch? (1 Viewer)

[sggoat]

So I get back to the rig from holiday shopping and try to start the truck-nothing-no click, nothing. I check the horn-nothing. Watch the ammeter and step on the brakes-nothing-no meter deflection- same with the headlights. I get out my little circuit probe and find power at the battery, alternator, starter, horn relay, and on the fuse block at the headlight/tail/turn fuses.(fuses are good) Now I'm kicking myself for not having a copy of the wiring diagram in the pocket.
I monitor the headlight fuse and push the brake pedal--the light dims, then comes back strong a second or two later.--same when I monitor the taillight fuse. I push the horn button also-same thing. Wiggle the ignition key on and off a couple of times and try the same thing-this time I get a little buzz from the horn--so now I do the wiggle and check in earnest--get the horns to finally blow--now I quickly try to start the rig with the key-boom! starts right up like there was never anything wrong. Drove home with no issues--so what's up? is the ignition going bad? Maybe the contact from the ammeter circuit going into the switch?
Anyone have a recommendation as to how to proceed? Can I rebuild the ignition sw/contacts, or do I need to have BENO send me a new one?

 

[Curt]

New switches are available from most online retailers for cheap. Could be an intermitten short, Had this very thing happen to me.

 

[bikersmurf]

The electrical switch is easily replaced. I'll explain in a PM if needed but I'll not post up how...

 

[honk]

Pending a new ignition switch it might help to disconnect the battery, squirt a bunch of contact cleaner into the switch and work it from off to start several times, then hook the battery up and see if it doesn't work like it used to.

 

[edwjmcgrath]

Headlights and horn don't go through the ignition switch. They should work with the ignition off.
Things that could cause your symptom are a bad fusible link, bad connection or cable on any of the "big" cables (power/gnd), or ammeter connection.
You can have a highly resistive connection in a cable and still read 12v. What will happen is that the voltage will drop dramatically when you turn the lights or horn on and the lights and horn will barely light or barely make a noise (as you saw). I would go through all of those cables and connections carefully.

 

[Pin_Head]

It sounds like a bad connection somewhere in the main power delivery line. The power comes from the battery through the fusible link to the amp meter, through the amp meter to the ignition switch where it splits into two lines. Half of the fuse block gets constant power, half gets switched power. If the horn, headlights and brake lights don't work, then the constant power side is not getting the juice. Check and clean all the power connections first.

X2 You can get fooled by measuring voltage on an open circuit when no current it flowing. Even a bad, high resistance connection in a circuit will show 12V, but it will drop to 0 when you turn it on.

 

[73tlcv8]

Where I would start based on the gremlins I have had:

first I would check voltage at + and - battery clamps not the post, while trying to crank the engine. If the voltage on the post is good and low on the clamp, take clamps off and clean.

The second thing I would check are the spade connections on the back of the fuse block. Those corrode and cause similar problems in other circuits. You have to take the two bolts out of the fuse block and pull it out to see them. Disconnect battery first to avoid sparks.

The third thing I would check is the chassis ground cable and the jumper from frame to the engine block.

After that you are chasing fusible links ignition switches and other hidden connections. Since you had trouble with the starter and headlights my guess is the + battery clamp to post or the red cable to clamp connection if it is not a factory type clamp.