Lights surging / Cant find cause

[Mullet]

1986 K 5 stock 305/700r4
All lights are surging/flashing. Headlights, tail lights, interior lights, even radio is doing it.
I have a new battery. I've checked the alternator with volt meter, and no surge at meter. I've cleaned and checked the grounds, and even ran an extra ground from frame/engine to body.

Any idea's on what the problem may be ?

 

[Mullet]

Anybody ??

 

[76k5blazerr]

Check your fuseable links, there are 2 or 3 on the truck. My 76 did the same thing and then everything just quit working all together, it was a blown fuseable link on the firewall. Also it used to do the same thing again and it was the battery cables.

 

[diesel4me]

In addition to the fusible links & battery cables (and the battery terminals,they must be shiny and clean!),I'd check for missing ground straps,one should be on the rear valve cover bolt to the firewall,and there is at least one ground wire from the headlamp harness and one off the negative battery cable that bolt to the radiator support above the headlamps..
There is often a ground strap from one of the front cab mount brackets to the frame also,that gets left off or broken,rotted off..

Seeing you added a ground and checked the rest,I'd say its a corroded "main power" wire or battery cable letting its high resistance block the flow of electrons and it "pulses" through the few remaining good strands of wires..a long shot is the alternator may have failing diodes,letting some AC sneak out along with the DC voltage,this may not show up on a voltmeter..(and it'll ruin the battery,eventually)..

 

[Mullet]

The fusible link on the firewall didnt look burnt out but the insulation showed signs of it getting hot. I put a good fusible link in place of it but no difference, lights still flickering. I took battery cables off and cleaned the ends and terminals, and even took the grounds off and wire brushed the contact points to insure proper grounding on the radiator support. Still flickering, and to make matters worse, the flickering seems worse after all that. I still have to check the valve cover bolt to firewall ground, but other than that I guess I'll have to live with it, I dont know what else to try.

 

[76k5blazerr]

The fusible link on the firewall didnt look burnt out but the insulation showed signs of it getting hot. I put a good fusible link in place of it but no difference, lights still flickering. I took battery cables off and cleaned the ends and terminals, and even took the grounds off and wire brushed the contact points to insure proper grounding on the radiator support. Still flickering, and to make matters worse, the flickering seems worse after all that. I still have to check the valve cover bolt to firewall ground, but other than that I guess I'll have to live with it, I dont know what else to try.

You might be surprised the difference that new battery cables would make. Even if the old cables look fine (mine did) they may not be good.