Check to make sure all your connections are clean. Grounds as well.

 

Are you religious? Know a Priest ? Exorcism, that's the key. Man, that's really strange.

Is the Starter Relay grounded properly ?

The headlights come right off the fusible link attached to the battery side of the Starter Relay.
The only way those headlights would go out is if there were no power from the battery or the Link was flakey.

Yeah, check that ground cable connection to the engine.
Check the Positive cable as well, they can look good but not be connecting in the middle.

From this view, I would replace both of them, and verify you have a ground strap going from the engine to the body.

 

I would for sure check connections, particularly grounds, and anything growing blue powder... but just had a thought. I'm also suspicious of the ignition switch, but it's only a secondary suspicion. The other thing I'm wondering is if anything thing has been rewired or unhooked and reconnected recently. Or if everything has been as is for awhile and this issue just popped up?

 

Are you DuraSpark or EEC ?

Ammeter gauge or Ammeter light ?

 

Your large wiring is fine since you bridged the posts and the starter turns over. That means your battery, battery cables, and all the large connections are good including the large grounds.

But you are losing power to everything else. Everything else is powered by a smaller wire tied to the large post on the solenoid that goes to the battery. If you follow this wire off the post, the first thing you will notice is a rectangle rubber thing in the wire. This is a fusible link. If you take the smaller wire off, and then pull on this rubber piece, if it stretches, it's burnt out. If it's ok, keep following this wire, you may have to unwrap some areas, and you will run into factory splices and more fusible links. Check the links and check the splices for corrosion.

 

Here's a link to a diagram. It's for a 1985 but yours will be very similar if not exactly like it. Page 17 will be what most trucks will have, it's been my experience most trucks have the gauge package. If you have lights instead of gauges you can use the other diagram on the page above 17.

Charge & Power Distribution (Gas) - Gary's Garagemahal (the Bullnose bible)

 

 

 

You can get replacement fuse links at the auto parts store in the electrical area or ask for them.

If you have no power to the inside of the truck you would also not have spark.
Yes clean ALL the cable ends starting at the battery to the start & motor & frame.
Power inside comes from one of the wires you cut the fuse links from. My guess it burnt again or they have a bad connection.
Dave ----

 

 

Oh yeah, that will cause your headlights to go out....
Are you religious? Know a Priest ? Exorcism, that's the key. Man, that's really strange.

 

On the high RPM disconnect the throttle cable as I have seen that hold the throttle open a little with a bent bracket. Start motor still high RPM?
If so shut it down and with motor off check to see if the choke is closed. Thinking it will be as the motor is cold.
Look at the 2 idle speed adjusting screws. 1 is for the fast idle when the choke is on and should be hitting a half moon thing with steps in it. Now open the choke by hand and this half moon thing should move and the screw no longer on the steps and the other screw should now be hitting the carb body.

See if you can start it with out hitting the gas, will it idle at a good RPM now? If you have to hit the gas, once running open the choke and see if the idle comes down to normal.
If the adjusting screw is hitting the carb body try adjusting in out to see if the idle will drop down.
If the screw is not hitting the carb body you will need to start looking for vacuum leaks.

With the motor running and a can of carb clean with the straw spray around the base of the carb, along the head & intake manifold. There is also a vacuum tree to the rear and under the intake manifold with hoses & caps. There is 1 cap that is vary hard to see back side to the motor that likes to dry out and crack and/or fall off check this really good.
Then spray any vacuum hoses / lines checking for leaks. The last if you have AC there is a vacuum reservoir on the right fender well, either a plastic ball or a metal juice can. I had the juice can rust out and had pin holes and caused a vacuum leak. I used fiber glass rosin to seal it and black paint looks new now.
Good luck
Dave ----
ps spray the EGR valve as someone had one that caused a vacuum leak also.
Oh if you find a leak with spray the RPM will change

 

Make sure you didn't dislodge or break a connection to a vacuum line while you were poking and prodding. May not find anything the first time or two, but follow each connection individually from start to termination and give it a thorough inspection.

 

Only issue I have with spraying for leaks is in my little experience, if the leak is large enough and in the right spot that the rpms are so high and it's running so rich that it won't notice a little bit if carb cleaner. Maybe if you went full flood and got enough in to bog it down? I'm going to make a smoke tester in the very near future and post it here if successful.