Lights and horn turn off truck

[Jengel1981]

1987 k20 camper special
Anytime I turn on the lights or hit the horn the truck cuts out. I've redone all of the grounds that I can find and replaced the light switch. Can anyone point me in the right direction

 

[dvdswan]

Welcome to the site. How's the alternator and charging system?

 

[chengny]

1987 k20 camper special
Anytime I turn on the lights or hit the horn the truck cuts out. I've redone all of the grounds that I can find and replaced the light switch. Can anyone point me in the right direction

A little background info always helps. For example:

Did this condition develop gradually - getting worse over time - or did you just wake up one day and it suddenly existed?

If it began one day and has been that way ever since, were any repairs/modifications done immediately prior to that point?

Do you have a gauge package, and if so have you been able to notice whether the volt meter drops when the lights/horn are operated? I realize that because the engine stalls if they are operated it would be hard to catch it. Try turning on the lights or beeping the horn with the ignition switch in the RUN position (but without the engine running) and then watch the volt meter.

Does the engine immediately stall or does it stumble along for a while and then finally give out?

When this occurs, how do you restart the engine? Do you just turn the H/L's off (or stop blowing the horn, as the case may be) and when you turn the key it fires right back up? Can it be restarted if the H/L's are left on?

Does this happen when either the parking lights or the headlights are turned on or is it just the headlights?

And like Dave asks, are the charging system and battery(s) okay? Because it is Camper Special, it might be equipped with an auxiliary battery - is this the case?

 

[Jengel1981]

The battery, starter, alternator, ignition control module, and light switch are all relatively new. The battery holds 12 volts when the truck is off and 14 volts when the truck is running and all accessories are off. The battery, starter, and alternator all went at the same time about 6 months ago, which i thought suspect. about 4 months ago the ICM went out and shortly there after the truck would shut off immediately when i turned on the lights. i replaced the switch but that didn't fix the problem. If i could get the lights to turn on then i could start the truck but noticed a 1 volt drop. sometimes, with the truck running, i could hold a very high idle with the gas pedal and turn on the lights but when driving noticed a voltage drop, as it felt like the engine didn't have as strong a spark and the lights would brighten apon acceleration and dim at idle. i did clean up all of the grounds that i could find: battery to starter, battery to frame and engine, frame to body, head light and tail light grounds nor have i found any frayed or exposed wires and still i havent eliminated the problem. there isnt an auxiliary battery. i just pulled the horn relay and it tested good but right now have no horn and the lights wont come on and it will turn over but it wont start. ill try to get more info when it does

 

[PrairieDrifter]

Do you have the ground strap going from the firewall to the back of the passenger side head?

 

[Snoots]

Are you getting 12v at the coil when it is running?

 

[Jengel1981]

I do have a ground strap from the passenger side head to the firewall. Additionally I ran a ground straight from the battery to the firewall.

 

[rich weyand]

I do have a ground strap from the passenger side head to the firewall. Additionally I ran a ground straight from the battery to the firewall.

Take out the second ground. A loop of ground wire acts as an antenna and picks up all kinds of electrical noise. Your grounds should branch like a tree, with no circles.

Make sure the ground connections are all shiny metal to shiny metal, then paint over them to protect them from water.

 

[donnieray]

Take out the second ground. A loop of ground wire acts as an antenna and picks up all kinds of electrical noise. Your grounds should branch like a tree, with no circles.

Make sure the ground connections are all shiny metal to shiny metal, then paint over them to protect them from water.

Dang, that's something to think about! I may or may not have added extra grounds, I'll be checking though. I miss the wisdom you are known to post. How have you been Mr. Weyand?