Turn the key. Nothing

[rampage]

Then I check the voltage at the positive battery cable and it's dropped to 7-9 volts. I wiggle the battery cable and it goes back to 12.6 and I can repeat this process over and over.

Where exactly are you measuring the voltage at - directly to the battery posts, on the battery cable clamps, or somewhere else?

... but turn the ignition and everything dies and voltage tested at the positive cable drops but it's 12.6 on the positive terminal.

This makes it sound like your measuring the voltage somewhere like at the firewall or the starter and then again directly at the battery post ... correct?

With that assumption in mind, if you are getting a voltage drop from say the firewall (or starter) to the battery post then you have internal corrosion in the positive battery cable and need to replace it. With internal corrosion it will allow some current to pass through (like to light your dome light), but once you try to pass a lot of current through it you get a large voltage drop due to the resistance created by the internal corrosion. Once the voltage drops below a certain level the ECM turns off - so no start.

Check the voltage at the starter and firewall both before and after you try starting it. The voltage should stay the same, if not then replace the offending cable.

 

[bjr34bass]

ok. I'm checking the voltage on the terminal itself (12.6) and the cable (still attached to the terminal) which drops after attempting to start the vehicle. Essentially the cable is part of the terminal at that point, so I'm confused why it reads lower voltage while the terminal itself reads 12.6

I haven't checked the voltage anywhere else yet after attempting ignition(it was late).

 

[Kain]

sounds like a bad cable, you might also have a load test done to your battery

 

[bjr34bass]

battery load tested. It's good.

 

[rampage]

Same basic rule applies, if there is a voltage drop between two points on a wire then I'd suspect a bad cable/connection/corrosion. Did you clean the battery posts and cable clamps? And I always apply a thin layer of dielectric grease between connections like the post and clamp to keep them oxidation free.

I know you said the battery was load tested but it's still possible that the battery is at fault with something like a loose battery post connection internally. If you have another battery you might want to swap them out to check that off your list.

 

[bjr34bass]

I cleaned the posts and cables, but I'm thinking I need to give the negative cable connection some additional attention. The cable connection to the terminal is oxidized pretty good.

 

[kennyw]

Sounds like a bad ground issue to me. Clean with a water and baking soda solution until there is no corrosion left. If that doesn't get it clean, replace the cable/connectors.

 

[bjr34bass]

Fixed!

I cleaned the shiz out of the terminals and posts. Fired right up. I'm telling myself that the NSS was bad too, but now I'm not so sure! Oh well. I'll replace that too. I took it out and jumped the wires. I'd just leave it the way it is, but I noticed the idle issues that I read about in other posts (Idle rev).

THank you everyone for your help! This was a good "get to know your blazer" project for this noob.

 

[diesel4me]

I've had battery cables that looked to be in very good condition externally,but had nothing but greenish white dust inside about 1" beyond the terminal for a half inch,with maybe 2 or 3 "good" strands of wire still "conducting"...

All I could get was a "clink" out of the solenoid when I went to start the truck,and only the dash lamps and interior lamp would light...then nothing would work...a few seconds later,the interior lamp came back on gradually,then it would "click" again..those few strands were doing the brunt of the current carrying and would get hot and build up resistance..
I hooked a jumper cable from the battery post to the stud the positive cable went to at the starter,and it fired right up...replaced the cable with a new one,no more problem!..

I also had the same thing happen on my '72 K5 once..everything went dead,including the starter,and it stalled,and I could not even push start it...after a hapf hour of head scratching,I found out whoever had it before me,had decided to swap to a top post battery--and they simply chopped off the side post terminal and crudely spliced about 6" of an old top post cable to it by soldering them with a propane torch and taping them together--the "splice" was well hidden under the battery tray...

When I saw tape there and unwound it,all that came out was white dust that was extremely irritating to inhale,like dried up battery acid!...I was able to cut the cable back and twist it together good enough to get home...

 

[bjr34bass]

A lot like my situation. I've got a top terminal battery with the splices on the negative ground to the front and one on the positive to the alternator. I took the front ground splice off (there was still slack enough) and got the green dust treatment from the end of the original cable. CLeaned everything better than I had and she fired right up!