72 Sierra Grande wiring - still at it

[Bigblock50]

I got the truck up on ramps today so I could lay eyes on the back of the solenoid. What I saw completes the picture of the incredible rewiring done by the PO soon after the truck was purchased.

First, I determined that the mysterious “blue wire” traveling with a yellow wire to the PO’s now-deleted “circuit junction box” is actually an intercepted version of a purple wire going to the NSS. LockDoc suspected this earlier. Using my continuity tester, I connected the tip of the blue wire to one of the NSS connector terminals and it lit up. I still can’t find where this weird and unsafe junction was made, or why. But I will find it.

Second, I found that the S terminal of the solenoid is connected to a black wire (mentioned in earlier notes) that was also connected to the “circuit junction box.” However, this black wire is now showing up as a ground. This could either mean an internal short in the solenoid itself or a faulty connection at the terminal. To determine this I’ll need to drop the starter.

To solve all this I plan to replace the solenoid and starter and find where the purple wire was intercepted by the blue wire - I think it’s in a wrapped area of the harness under the hood. I will then splice in a correct purple wire and run it to the S terminal of the new solenoid. I believe the truck will then start.

Why the truck was rewired in this Horrible manner boggles the imagination. But I believe the problem has been found thanks to much help from LockDoc and others on this forum. I’ll send a final note when I get the repairs done.

Bill in Luray

[Bigblock50]

Picture of the hidden splice. Firewall on the drivers side, inside continuous tape.

[Bigblock50]

A week further down the road, the "truck that keeps on giving" is still at it. As discussed in earlier messages, I've corrected the purple wire situation so that the solenoid S terminal now gets a feed directly from the neutral safety switch. That wire had indeed been spliced into under tape, converted to a blue wire, and inserted into the PO's rats nest aftermarket junction box. See attached picture of the hidden splice. That purple wire now goes directly to the solenoid.

Following that, I replaced the burned out fusible link and connected up the junction box so I could try the starter circuit. I didn't get that far. Instead, when I closed the negative side knife switch, I got a major league short and blew the link again. I lifted the leads at the junction box and used my continuity tester, which showed that the red "12R" wire did in fact have a connection to ground. I haven't been working on that circuit in any direct way.

With LockDoc's diagnostic help I thought I had the ignition circuit fixed. I may have, but I can't test it until I can figure out why there is serious short to ground in the "12R" wire with the ignition switch in the off position. I'm spending more time on this than running my farm!

Suggestions welcome on a good procedure. What's the expression, so close and yet so far?

Bill in Luray

[LockDoc]

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If you haven't already I would seriously consider getting rid of the adapter for the camper tail light wiring that I pointed out in post #10 . Also, if you still have more than one wire going to the "BAT" terminal on your HEI I would disconnect all of them except the main power wire, unless you know for sure where they come from. (in post #13 you mentioned that it had "several wires attached")

LockDoc

[Bigblock50]

I’ll try disconnecting the camper plugs today. The red wire you saw near the HEI doesn’t connect there - it goes to the electric choke on the Edelbrock carb.

More later if I have time to work.

[Bigblock50]

I had some time and made what I think is progress. As to the sparking when connecting the battery ... that seems to be generated by the aftermarket radio that’s connected to constant power. It has some kind of internal battery that wants charging. If you tap the battery post multiple times, it only sparks on the first tap. When I just left the battery fully connected, nothing bad happened. Turning on the ignition switch to “on” powered up the heater, wipers, etc.

That brings us back to the purple wire starting circuit. As reported above, when I started this repair job, I found that one of the purple wires had been spliced into by a PO and changed to a blue wire that went into a junction box. This meant that at the neutral safety switch, one terminal was hot when the ignition was “on,” but the other remained dead when the ignition was turned to start. I re-spliced that wire and took it to the solenoid per the original circuits. Today, when I was confident I didn’t have a short, I gave the ignition switch a try. Solenoid did not activate. Checking the two contacts at the neutral safety switch, it seems I now have the opposite situation. With the ignition switch “on,” both contacts are cold when one should be hot. With the ignition switch at “start,” one contact goes hot but not the other.

Underneath the dash, I see both 12ga purple wires leave the NS switch and run together behind the fuse box. But only one of these wires emerges through the bulkhead connector. Is that right? I can also see a 12ga purple wire at the back of the ignition switch. The factory wiring diagram is not all that helpful on where actual wires run and that’s the issue when a PO has rewired everything. I think the truck will start and run if I can get the other NS terminal to go hot with the ignition switch “on.”

[LockDoc]

Originally Posted by Bigblock50

I had some time and made what I think is progress. As to the sparking when connecting the battery ... that seems to be generated by the aftermarket radio that’s connected to constant power. It has some kind of internal battery that wants charging. If you tap the battery post multiple times, it only sparks on the first tap. When I just left the battery fully connected, nothing bad happened. Turning on the ignition switch to “on” powered up the heater, wipers, etc.

That brings us back to the purple wire starting circuit. As reported above, when I started this repair job, I found that one of the purple wires had been spliced into by a PO and changed to a blue wire that went into a junction box. This meant that at the neutral safety switch, one terminal was hot when the ignition was “on,” but the other remained dead when the ignition was turned to start. I re-spliced that wire and took it to the solenoid per the original circuits. Today, when I was confident I didn’t have a short, I gave the ignition switch a try. Solenoid did not activate. Checking the two contacts at the neutral safety switch, it seems I now have the opposite situation. With the ignition switch “on,” both contacts are cold when one should be hot. With the ignition switch at “start,” one contact goes hot but not the other.

Underneath the dash, I see both 12ga purple wires leave the NS switch and run together behind the fuse box. But only one of these wires emerges through the bulkhead connector. Is that right? I can also see a 12ga purple wire at the back of the ignition switch. The factory wiring diagram is not all that helpful on where actual wires run and that’s the issue when a PO has rewired everything. I think the truck will start and run if I can get the other NS terminal to go hot with the ignition switch “on.”

I'm betting the NSS needs adjusted. Did you try starting it in neutral?

If the NSS needs adjusted there are two small hex head screws that hold it to the mast jacket. If you loosen those two screws the switch will slide back and forth a little bit. That is how you adjust it.

You could also disconnect the connector with the two purple wires and put a jumper wire in the connector as cj847 shows in post #3. Just remember when that jumper wire is in place it will start in gear so be careful.

LockDoc

[Bigblock50]

LockDoc - I'll try the jumper tomorrow, forgot about that option. The NSS switch itself is good/new but the detent Park position in the transmission is well-worn and loose. You have to hunt a bit to set the NSS.

One question, though. If I test the purple wire contacts with the dual connector detached from the NSS, which result should I see with the ignition switch in the "on" position?

(a) Both contacts cold
(b) One contact hot, one cold

In my test today I got result (a).

[RustyPile]

Originally Posted by Bigblock50

LockDoc - I'll try the jumper tomorrow, forgot about that option. The NSS switch itself is good/new but the detent Park position in the transmission is well-worn and loose. You have to hunt a bit to set the NSS.

One question, though. If I test the purple wire contacts with the dual connector detached from the NSS, which result should I see with the ignition switch in the "on" position?

(a) Both contacts cold
(b) One contact hot, one cold

In my test today I got result (a).

Let's review just how the start circuit works.. Starting at the ignition switch - the "big" red wire feeds power to the ignition switch directly from the battery.. It's "hot" all the time.. Turn the ignition switch to "ON" and the red wire feeding the HEI becomes hot.. The purple wire coming from the ignition switch is hot ONLY in the start position.. That purple wire feeds power through the NSS to the "S" terminal on the starter solenoid.. The NSS is a simple off/on safety device.. It prevents power being applied to the purple wire going to the starter solenoid unless the transmission is in either PARK or NEUTRAL..

So to answer your question -- Neither of the purple wires are hot with the ignition switch in the ON position..

If your shift linkage has a lot of slack and wear, you're gonna have one heck of a time getting the NSS adjusted properly..

[Bigblock50]

Thanks, that's very clear. I found a nice diagram that other forum users might appreciate, so I've attached it.

On the NSS, you often have to push the shift lever a bit further to the left to start the truck. It's not much of a nuisance for me, I just have to remember it.

[RustyPile]

Originally Posted by Bigblock50

I’ll try disconnecting the camper plugs today. The red wire you saw near the HEI doesn’t connect there - it goes to the electric choke on the Edelbrock carb.

More later if I have time to work.

Bigblock50, refer to your post #11... You posted a diagram of how the distributor is hooked up to the harness.. The diagram shows 2 red wires connected to it.. Those are the 2 wires LocDoc is referring to.. The old points type ignition had 2 wires -- a resister wire and a yellow wire connected to the coil.. I don't know what you actually have, but I've never seen a distributor wired like that..

[Bigblock50]

I hadn't focused on that part of the diagram ... perhaps not the best representation of a fused power connection. In any event, my HEI is connected to power by a single sliding connector at the end of a black wire. You have to remember, rewiring on my truck was done in a variety of wire colors having no relation to GMC diagrams. The substitute for the 12ga purple solenoid wire was a thin black wire about 18ga inserted into one of 3-4 aftermarket junction blocks.

In any event, today the truck cranked over fine and all electricals seemed OK. The new starter grinds a bit but that's an adjustment issue that I can sort out. I have a few leftover wires spliced together under the hood (yellow, blue, green) that I think are connections to trailer lights/signals. I'm abandoning the underbody trailer hitch wiring in place.

Like most long-time collectors, I've encountered many problems caused by shoddy work in the past. This pernicious job of rewiring takes the cake.

Thanks to all who have helped, most especially to LockDoc and Rusty Pile!

Bill in Luray

[LockDoc]

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Glad you have the truck so it will crank over now. That is a step in the right direction. Let us know if you have any other questions.

LockDoc

[VetteVet]

Here is a write-up and some visuals that may help.

http://67-72chevytrucks.com/vboard/s...d.php?t=655903