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Need some help 98 6.5 electrical-need to hardwire my truck

Smokinthehippies said:
Yes. Once it does the "stumble" you basically get one last chance to put it in run, but as soon as you click to start all electrical inside goes away.


I did that on both of them. I found no high resistance spots anywhere.


I don't think it's the pmd. A. It is already relocated B. It's an electrical shutdown, not like the truck isn't getting fuel
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1) Ok.

2) If you find that they are conducting as they should, and not-conducting where they shouldn't be, the switch should be fine. :dunno:

3) On a 6.5 engine, there is no such thing as an "electrical shutdown." They *always* stop from lack of fuel (unless your engine is in pieces :rolleyes:). If you lose electrical power, it behaves just like you turned the key off. If you lose the PMD, it behaves just like if you turned the key off. If your battery cable fails it behaves... (you get the idea).

The PMD is one of the few things that is operating during both the start and run cycles. Most everything else gets shut off. So we don't have many options, electrically, if it is failing during a start cycle.
 
But how does that explain that it's completely crap until I replace the switch and then works perfectly again? Could the pmd failing cause the ignition switch to blow? And then it's fine til the pmd acts up again?
 
Smokinthehippies said:
But how does that explain that it's completely crap until I replace the switch and then works perfectly again? Could the pmd failing cause the ignition switch to blow? And then it's fine til the pmd acts up again?
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That's what I'm wondering. But you just said that your old switches are passing their continuity testing. So are they really blown? :dunno:
 
Smokinthehippies said:
Idk. I'm not seeing a failure point and they all pass the ohm test
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Soooo...what happens if you swap one of your old switches back in? Is swapping the switch actually helping? Or is this just an issue that is going away by itself after some time? Or maybe arcing on the connectors? But you'd probably see that. :dunno:

When the engine dies, it is just the engine, or does the entire cab go black?


Side-note: Are you getting fast at swapping switches yet? :doah:
 
campfire said:
Soooo...what happens if you swap one of your old switches back in? Is swapping the switch actually helping? Or is this just an issue that is going away by itself after some time? Or maybe arcing on the connectors? But you'd probably see that. :dunno:

When the engine dies, it is just the engine, or does the entire cab go black?


Side-note: Are you getting fast at swapping switches yet? :doah:
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Well now I don't have any that I haven't dismembered. Once it goes, they've not worked again. Its just the engine, cuz this time for sure the radio stayed playing.

And yeah I can do start to finish in under 15 minutes now.
 
Smokinthehippies said:
Well now I don't have any that I haven't dismembered. Once it goes, they've not worked again. Its just the engine, cuz this time for sure the radio stayed playing.

And yeah I can do start to finish in under 15 minutes now.
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The radio stayed on? Doesn't sound like a failed switch if the radio is still getting power. Sounds like something downstream. Unless the switch has multiple outputs. I think we've arrived at the point where we need a schematic.
 
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campfire said:
The radio stayed on? Doesn't sound like a failed switch if the radio is still getting power. Sounds like something downstream. Unless the switch has multiple outputs. I think we've arrived at the point where we need a schematic.
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But then once the truck turns off and goes back to start it's definitely an electrical issue as the entire dash has zero lights or any kind of recognition of there being a key or power to the dash.
 
Hey Ethan, thanks for all of your help with this so far.
I'm really at a loss on this which is unfortunate as I need to get it reliable as its my only vehicle for work.
I'm ok replacing the PMD it I need some better evidence that it could actually be cussing the issues. I can't keep throwing parts it especially since I might be stuck taking it to a shop for repair (really don't want to)
 
Smokinthehippies said:
Hey Ethan, thanks for all of your help with this so far.
I'm really at a loss on this which is unfortunate as I need to get it reliable as its my only vehicle for work.
I'm ok replacing the PMD it I need some better evidence that it could actually be cussing the issues. I can't keep throwing parts it especially since I might be stuck taking it to a shop for repair (really don't want to)
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1) You're welcome. For me, troubleshooting is a way of life. :D

That being said, I've never owned a truck this new, and I have hardly any experience with them. So I can talk you through possibilities, but I don't have any particular insight or knowledge of common failure points for this model. My rigs don't have PMDs or ignition issues. Or a lot of other features that you enjoy. :haha:

2) We aren't going to know what is downstream of the switch until we have a schematic to check things against. But I don't think you have many options.

3) Check your phone. :waytogo:
 
Not sure whether these diagrams are correct (they're fairly generic), but this illustrates what we're looking for:

0996b43f80231a24.gif


0996b43f80231a23.gif
 
Looking at diagram 4, the ignition switch should be connecting terminal "D" (RED) to terminal "C" (PINK) when the switch is in the run position. It should be connecting terminal "D" to terminal "A" (PURPLE) when in the start position.

Don't know how trustworthy the color identifiers are (they did change from year to year), but that should give you something to test. If your switch is failing to connect terminal D (input power) to the others, that tells you the problem is inside the switch.


As for what causes the problem, we'll have to trace our way through the schematic downstream.
 
I'd look closely (and wiggle) the wires that have the fusible links in them at the solenoid and firewall,and make sure the red wires from the ignition switch terminals "B" and "D" ,that go "to battery",for any shorted rubbed through spots, or failed splices...the power wires often corrode where they enter the fuse box too...they'll carry current for a few minutes,heat up,then break the connection..junkyards here sell lots of fuse boxes..(if they have any good ones!).

I've had "half blown" fusible links cause similar symptoms,the power is lost to the ignition and most of the cab wiring after the few "good" strands left got too hot,and the connection would break...it was frustrating as hell to diagnose..
 
diesel4me said:
I'd look closely (and wiggle) the wires that have the fusible links in them at the solenoid and firewall,and make sure the red wires from the ignition switch terminals "B" and "D" ,that go "to battery",for any shorted rubbed through spots, or failed splices...the power wires often corrode where they enter the fuse box too...they'll carry current for a few minutes,heat up,then break the connection..junkyards here sell lots of fuse boxes..(if they have any good ones!).

I've had "half blown" fusible links cause similar symptoms,the power is lost to the ignition and most of the cab wiring after the few "good" strands left got too hot,and the connection would break...it was frustrating as hell to diagnose..
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If he was popping a fuse (of any sort), wouldn't he be dead in the water permanently? This problem keeps going away for short periods of time. :dunno:
 
If he was blowing fuses,yes,it would stay "dead"...but wires can get hot and break the circuit like a breaker or thermal overload at times,when they get toasted from a dead short that didn't last long enough to completely fry it-- or corroded at connections, and cant handle a load for any length of time..
 
diesel4me said:
If he was blowing fuses,yes,it would stay "dead"...but wires can get hot and break the circuit like a breaker or thermal overload at times,when they get toasted from a dead short that didn't last long enough to completely fry it-- or corroded at connections, and cant handle a load for any length of time..
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What he's reporting is that the switches themselves are frying. 3 times in a row, replacing the switch has made the problem go away. For a while.

I'm suspecting that something downstream is overcurrenting and frying the switch. But that should blow some fuse before it would damage the actual switch. Right? :dunno:

The sudden death and recovery of the fuel supply is what made me think of PMD issues. But temporarily losing power to the PCM or PMD would also cause the same symptoms. I just don't understand why the switches would be failing. :dunno:
 
Seems like the problem is occurring in the start position so here's a diagram of that

image.jpg
 
Ignition switches can and do go bad in this body style, but its due to mechanical wear and not shorting out. I just changed one in my 97 Tahoe because it would turn off while the truck was running, but it lost everything, not just the engine. If your switch is bad, the engine will not turn over in the start position.If your engine won't turn over and the truck is entirely dead (including the interior lights), also try tightening up your battery terminals. The side posts are famous for having a crappy connection that can arc open when you hit the starter.

That said, I am sure you need to replace your PMD. It's the cause of your problems. Even relocated they can still fail. The fact that your truck starts again after you change the ignition switch is by happen chance. As they cool down, then the PMD will come back to life. I am willing to be you'll wind up hacking up your harness for no good reason and it'll die again on you shortly afterwards. I know the PMD is bloody expensive, but I am sure enough this is your issue that I'll pay for it if you put it in and the problem persists.

Replace it with a grey model PMD. They are better than the black ones with improved drivers and self cooling capacity.

http://www.hdiesel.com/P/NewStanadynePMD/827
 
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