This just blows my fuse...

[overtimeracing]

Hey guys... I hope you can help me. My mother (73) has a 96 S10 Blazer. She resently had the engine replaced with a used 4.3 from a local guy. She drove it for about 2 weeks with no problems. One morning I had to move the Blazer so i could work on some of my junk. Started it, moved it, and parked it. Later I was going to go to the parts store, so i thought i would take her Blazer and it wouldnt start. Wont even crank. Tried to jump, with no luck. I guessed the starter was bad, so I brought it into the garage and replaced the starter. No change. My buddy told me to check for a blown fuse and sure enough, there was a 10a fuse marked crank, blown. Replaced the fuse, and it started... once. Now it continues to blow fuses, and wont start. I pulled the start wire (purple) and checked its condition and it seems o.k. (I expected to find it burned to the exhaust manifold but no such luck.) Even disconnected from the starter, it still blows the fuse. I've followed the wire up to where it goes into the large harness. Nothing seems crimped, burnt, or broken. I dont know what to check next. I hope someone has experienced this before and can help. Thx...OTR

[ofnaman]

I'd start by checking the grounds on the engine, all of them. There is a good chance one of them may have been left off or not fastened securely. There are a couple of grounds on the back side of both heads that are very hard to access and if you don't know what your doing when removing the engine you could damage them. Also, if your not really familiar with those grounds they could have been overlooked when going back together as you cannot really see them with the engine in. Other than that check the harness to make sure there is no obvious damage to it.

[overtimeracing]

Thats a good place to start. I'll do just that. Thank you...OTR

[gchemist]

Yup, bad ground somewhere. Good luck tracing it!!

[overtimeracing]

I looked... no grounds on the back side of the heads, Really couldnt "see" them anyways but one on each side of the intake manifold. Parts guy told me it was an ignition switch. Gonna try that i guess...

What if I try running a ground right to the starter?? Maybe??

[68C15]

that fuse is powered when in crank only. it feeds to the air bag module (computer) and the neutral safety switch. it's route to the NSS it goes from the firewall to a connector (7 way round) and then down the top driver side of tranny to the NSS. check for a hanging harness possibly melted against the exhaust pipe or if $wd damaged by the driveshaft

[overtimeracing]

Thank you...

[overtimeracing]

68C15... Thanks for the replies. I looked tonight, the harness on the drivers side is ok. Not burnt or damaged. Should I replace the NSS? Auto Zone lists a starter relay for this but I cant seem to find it. The three on the firewall are for the AC according to the Hates Manual. Any ideas?? Thanks again...OTR

[fixit-p]

Poor grounds wont blow the fuse, either a short circuit or over amp condition will. Here's a schematic of the start circuit, yours should be similar. Try locating the starter relay and remove it and see if the fuse still blows if yes then you know its the wiring up to the relay.

[overtimeracing]

Fixit-p... Thanks for the reply... I replaced all three relays one at a time with a new one and still blew fuse. I did notice the one relay had the wires, Red, Black, yellow, and Purple, and seems to match your schematic. I will unplug tomorrow and try again. Thanks again for your help...OTR

[68C15]

FYI, when replacing the NSS on these trucks you better plan on replacing the wire pigtails at same time. as a matter of fact if you get the connectors off without damaging anything I will ask the moderators to change your name to "El Conquistador".

chasing the cause of a blown fuse is fun. some people do it the red neck way by substituting a higher amperage fuse until they see smoke. (bad idea for obvious reasons) I use a wiring diagram to tell the destinations and look at those first. next I use my fault finder. it is a cool expensive tool that induces a pulsing current into the circuit at the fuse while I run my test tool (like a very sensitive magnetic field sensor) along the harness. when it stops beeping I have found the spot and start digging.

I am suspicious of the NSS or as GM calls it the trans range sensor

[overtimeracing]

I checked the wiring harness going to the starter relay. All checked out except the yellow wire. When I test with a test light, it lights when I put power to it (grounded.) The schematic shows it goes to the NSS. I unplugged the NSS and retested the yellow wire and the yellow wire was no longer grounded. I tried to crank over the engine but the fuse still blew. I would think with the NSS disconected, it should act like i was trying to start in drive. No crank, no blown fuse. What do you all think? Thanks again for the help...OTR

Oh buy the way...68C15.. you may call me "El Conquistador". LOL... Thanks for the help...

[68C15]

El Conquistador, when you unplug the NSS you remove the relay and the ground from the circuit. power comes from the ignition switch, through the crank fuse, to the NSS, the relay windings, and finally grounds G104 and G102.

let me get this straight. with the relay unplugged the yellow wire is grounded?! not good. then you unplugged the NSS and the ground went away? the short to ground is up stream of the NSS connector. this could include the NSS itself, wiring, or the airbag module.

with NSS unplugged jumper pins G (yellow) and E (purple), then retest for ground at yellow wire at relay (with relay unplugged). if it is grounded then you have a short up stream of the NSS. next I would leave all the previous leads and jumper in place and unplug the air bag module (pass. kick panel). if the ground goes away the module is bad. if not then PM me for my # and we can do the rest (gets too lengthy to type) over the phone.

[fixit-p]

It would be normal for the yellow wire to flow to ground because it has continuity through the relay coil to ground. As 68c15 said "when you unplug the NSS you remove the relay and the ground from the circuit" so that means the short is in the purple wire between the fuse and NSS. With the NSS disconnected remove the start/crank fuse and check the purple wire for continuity to ground.

[overtimeracing]

From 68C15: "let me get this straight. with the relay unplugged the yellow wire is grounded?! not good. then you unplugged the NSS and the ground went away? the short to ground is up stream of the NSS connector. this could include the NSS itself, wiring, or the airbag module."

That is correct. I will try your further tests (as well as suggestions from fixit-p) and get back to you guys asap. Thanks again for all your help...