There's a needle in my haystack

[benaustic]

A week or two ago, I posted about an electrical blackout in my K2500. I thought it had to do with the fuel pump circuit. It doesn't. However, thanks to Kennedy's help, I now have the right lift pump (a nifty little accidental discovery that may save the IP in the long run).

Symptoms... Here's what happens: at (seemingly) random times, not all that often, all electrical instantly goes totally dark. The transmission position light may *try* to light a little, but barely.

Momentarily disconnect batteries then reconnect them and all power comes back on. HOWEVER- once or twice, all *may* (not always) click back off again as soon as the glow plugs light. Repeat the process maybe once, maybe twice and we're back on the road like nothing ever happened.

This truck will make a 2000 mile trip in less than 2 weeks. :eek:

Can anyone tell me which part of the haystack I should begin looking in?

[john8662]

Ignition switch, power distribution box under the hood on the driver's side (check all big lug wires).

[benaustic]

I'll check the lugs. Already replaced a couple relays in the distribution box. Had a similar thing happen on an old White/Volvo semi that turned out to be a weak relay, so I thought I'd start there. I was wondering about the ignition. Any way to test/diagnose that without tearing the steering apart?

[HeavyChevy95]

'96 K2500 Frankentruck....
Could you be a bit more specific?

"blackout" what do you mean exactly and does the engine continue running or not at all?
Details..

I know a faulty head lamp/dimmer switch will have you taking chunks out of the leather seats at 4am while doing 75mph down a suddenly pitch black interstate. Not a light in sight, but engine and cruise keep motoring along as if nothing is wrong...
IIRC, my orange wire was crispy brown, the electrical connector was melted. The OEM lighting is barely (not) up to task so avoid neglecting lighting harness's (deterioration, damage, fray, shorts) and blown bulbs.

[benaustic]

OOOooooOOOOoooh... That makes me wonder! I have a bad stop/turn on the left rear! But no, engine and everything quits like one of those bad UFO sighting stories. No spit, no sputter, no jolt, just like a lightswitch everything quits and we slowly roll to a stop.

Could it be the tail light!? Come to think of it, it only happens when I'm on the brake (like at startup) or turning (or slowing down to turn). That would be so awesome. Tail needs fixed anyway. I'll start there and see what happens!

[a5150nut]

I'll check the lugs. Already replaced a couple relays in the distribution box. Had a similar thing happen on an old White/Volvo semi that turned out to be a weak relay, so I thought I'd start there. I was wondering about the ignition. Any way to test/diagnose that without tearing the steering apart?

Ignition switch is on the lower end of the steering column not in the wheel. Down near brake pedal has a rod from the key tumbler runs down column into ignition switch. cheap, easy part to change out.

[trbankii]

Ignition switch is on the lower end of the steering column not in the wheel. Down near brake pedal has a rod from the key tumbler runs down column into ignition switch. cheap, easy part to change out.

Having just done this last week, I certainly would not use the word “easy”...

[benaustic]

I'm replacing the ignition switch now. A5150NUT... I wouldn't call it easy... or cheap! $130! Crap-ola.

[trbankii]

I picked up a switch at NAPA for $20. But the steering column doesn’t drop far enough to make getting at the switch that easy - particularly trying to “blindly” get the wiring harnesses to disengage. It did go back together easier than it came apart.

[phantom309]

I'm replacing the ignition switch now. A5150NUT... I wouldn't call it easy... or cheap! $130! Crap-ola.

Whaaaa?? not sure if you are replacing the right part at $130,..
but good luck,.

[Dvldog8793]

There is a small plastic switch mounted under the steering column that is contacted by a steel rod from the ignition tumbler KEY switch. Judging by the price you paid, I am thinking you got the Key switch...? This probably isn't the problem. Most likely the small switch in the bottom of the column.

[a5150nut]

Whaaaa?? not sure if you are replacing the right part at $130,..
but good luck,.


GMPartsDirect item 23
http://www.gmpartsnow.com/chevrolet/k2500-pickup/1990115/1994-year/silverado-trim/6-5l-v8-diesel-engine/electrical-cat/switches-scat/?part_name=ignition-switch

[benaustic]

Went to O'Reilly's, looked up ignition. Said the part that fails most often is the switch incl. the wiring harness to below steering column. Thought I'd plug it in and test it, if nothing changed then I'd take it back. Unfortunately, I broke the brittle plastic plug on my old one getting it out, so I spent $130 for nothing. You read it right, nothing changed. Oh, and I replaced the rear tail/turn/stop. Also replaced the relays in the box on driver's side fender. After all this it's now worse than it was. Power comes on but blacks out when I hit the glow plugs. Tomorrow I'll look for a short there, but I really don't think that's the issue.

Speaking of glow plugs, I have a question. But first, background story: the engine I removed from this truck had glow plug module removed and replaced with manual switch in the cab. When I fixed the wiring, I decided to put it back to factory and bought a new glow plug control module. I hooked up the yellow wire (that is, the signal that turns on the GP's) from the ECU just like factory, however, I hooked up the key power through the manual switch that the previous owner had put in. In other words I can override the ECU GP signal by letting off of the manual switch, but as long as I hold the switch, GP's cycle normally. My logic was that this would prevent the GP's from cycling after startup and make GP's last longer. My question is this: Could this in any way piss the computer off? Could I have caused an ECU issue inadvertently?

[DmaxMaverick]

If you send direct power to the GP controller at the ECM pole, you may have fried the ECM. The correct way to do this is with a relay, that won't back-feed power to the ECM. Some get away with it, but many don't.

[benaustic]

Okay, I hear you on that. But my switch can only cut power to the GP's, not force power. And, it is not tied in to the signal wire from the ECM. There are three wires in the plug on the GP controller: yellow (ECM signal), black (ground) and orange (key power). My switch simply supplies the orange wire at my discretion. I don't see how I would be feeding any power to ECM. Rather, my concern was that ECM is signaling glow plugs to "on", but I'm not allowing them to come on by virtue of cutting key power and I wondered if that would cause an ECM issue.

[benaustic]

A5150nut- I followed your link. That picture doesn't do much for me, this one's better: http://www.gmpartsnow.com/oe-gm/1990115 . But I still can't really tell what that is. I'm assuming it's the key cylinder.

The reason I got the part I did is b/c when I took it apart, the key cylinder appeared to be working fine. Best I can tell, the key cylinder is completely mechanical and it mechanically turns the ignition switch ( http://www.oreillyauto.com/site/c/detail/BWD0/CS589/02018.oap?year=1996&make=Chevrolet&model=K2500%2BPickup%2B4WD&vi=5002386&ck=Search_02018_5002386_261&pt=02018&ppt=C0039 ) like it's supposed to. I saw no reason to suspect the key, so I went to the next logical place- which is the part I got. Am I missing something?

[trbankii]

There is a small plastic switch mounted under the steering column...

That should be “mounted on top of the steering column…”

That’s what makes replacing it such a bugger. ;)

[benaustic]

Sorry fella's. Just now noticed Dvldog8793's post from last night. I'll check this out.

[phantom309]

you say it blacks out when the glow plugs come on,.

Is the ground from cab to frame to motor good?

[a5150nut]

A5150nut- I followed your link. That picture doesn't do much for me, this one's better: http://www.gmpartsnow.com/oe-gm/1990115 . But I still can't really tell what that is. I'm assuming it's the key cylinder.

The reason I got the part I did is b/c when I took it apart, the key cylinder appeared to be working fine. Best I can tell, the key cylinder is completely mechanical and it mechanically turns the ignition switch ( http://www.oreillyauto.com/site/c/detail/BWD0/CS589/02018.oap?year=1996&make=Chevrolet&model=K2500%2BPickup%2B4WD&vi=5002386&ck=Search_02018_5002386_261&pt=02018&ppt=C0039 ) like it's supposed to. I saw no reason to suspect the key, so I went to the next logical place- which is the part I got. Am I missing something?

Same as in my link part 23

[benaustic]

Finally getting back to work on this issue. Phantom309: Yes, grounds are good.

I have A5150nut's suggested part in hand... came inside to do some internet learning to find the dern thing. Dunno if I'm any smarter or not, but I'm going to go back out and dig.

Any help would be appreciated.

[benaustic]

Nevermind. The culprit was a corroded batt. cable the whole time. Bah.