Replaced Dash Harness - truck wouldn't start

[lks dcvn]

So I was feeling ambitious over the weekend and replaced the dash harness on the Blazer...

Got the old one all out in one piece and then when I installed the (stock) replacement (used non-cut full gauge harness) the truck wouldn't turn over...nada - no click - nothing.

It does have a HEI ignition - but I thought the wiring was changed in the engine harness to make that operable...not the dash - guess I thought wrong. When you look at GMCPaul's site - it doesn't say that you need to buy a dash harness with a HEI distributor...

I ended up taking out the wiring and putting the old stuff back in (it started with the old wiring back in) to get it back into the garage...

What should I look at between the two harnesses to see what needs to happen to get this 'newer' dash harness installed? The wiring on my Blazer works well - it just looks like colored spaghetti under the dash and I would like to clean it up.

I also broke my plastic oil pressure line fiddling with the wiring harness... and it sounds like I have to replace it instead of fixing the end that attached to the gauge.

[GMCPaul]

Look at your power wire feeding the HEI distributor and trace it from the distributor to whoever the previous owner sourced power for it most likely they did not plug it into the fuse block on the ignition fused spade terminal and have spliced it into a portion of the underdash wiring harness, and I would bet they spliced into the ignition switch wiring.
To solve the problem cut where they spliced into the under dash harness and put a female spade terminal on it and plug it into the ign fused male teminal available on your new fuse block.
In regards to the plastic oil pressure line that is commonly found as a replacement to the metal line, you should be able to cut the plastic line with a razor blade then inside the nut that tightens line to gauge you should see a brass sleeve on the broken part of plastic line cut the plastic line out of it slide freshly cut end of plastic line through nut, place sleeve on plastic line sticking through the nut then insert line with sleeve onto it into gauge and tighten the nut. Done similar repairs many times as described without any problems.
If you can't solve it leaking then we do carry NEW metal oil pressure lines on the following page of our web site
http://www.gmcpauls.com/instrument_panel.htm
Part#2721918
GMCPaul

[GMCPaul]

PS- on the oil line heat the sleeve/ferule in oven or with a propane torch slightly to cause it to expand then holding it with pliers to prevent burned fingers re-insert it onto the line.

[lks dcvn]

Thanks for the reply - the problem is - there were no splices to the dash harness itself...

The dash harness came out in one piece without any cutting from any external wires (from the firewall, etc.) - that was why I thought the replacement harness would work without issues...

I will trace the wire tonight (from the HEI) when I get home and see where they end up - they do connect to the engine harness at the firewall - but it isn't pretty...

[bouncytruck]

I didn't do it!!!

The wiring, as I mentioned a long time ago, was/is sketchy. I replaced the whole disty, but I don't remember replacing or tracing the source wire.

I always planned to ditch the three gauges and get some new ones. I did run a new hose and fitting once because I broke it when I was working on the wiring.

[lks dcvn]

lol bouncy - no mention as to who did the previous wiring work - but Yikes!

I was trying to clean up the interior wiring - tired of looking at it the way it is... and I just had a gut feeling that there would be issues...

I would love to just rewire the whole truck - but I have some other projects (including a LWB that I am building for my Dad - he doesn't know it yet) that I need to get done before I tackle that project.

I figured replacing the dash harness would be an easy way to alleviate some of the spaghetti issues under there.

It would appear that the stupid oil pressure line has been a PITA before...

[bouncytruck]

When I got the truck, it had a toggle switch to start it. You had to put the ignition in just the right place and then hit the toggle switch to engage the starter. Of course, the PO by passed the neutral safety switch so you could hit the toggle any time, and the type of switch he used could stay in the "on" position so the starter could just keep on going.

I believe all that was done because he didn't know how to remove the ignition. I replaced the ignition, removed the toggle and wired back in a neutral safety. I never got around to putting a stereo into it, mostly because i couldn't stand to look at the rat's nest of wiring under the dash.

[lks dcvn]

Interesting...this might get comical moving forward. I will keep you posted and hopefully we can get this thing running.

If pix will help - I can post them up...

Finger (and wires) crossed -

[DANTES JIMMY]

no click or nuthin wouldnt that have more to do with the ignition feed than the hei feed??

[bouncytruck]

Check the neutral safety wiring. The factory harness might have a different way of connecting the neutral safety. Since the truck has a B&M shifter, it isn't wired into the column.

[lks dcvn]

Here is what I am working with...

There are only 2 wires on the front engine harness that connect to anything...

Purple wire is spliced to the light blue wire which runs under the truck to the B&M Hammer shifter (NSS is my guess)...another blue wire comes from the same area under the truck and runs to the starter.

White wire is dedicated from the firewall to the HEI...

This wiring really is pretty interesting - I am surprised this thing runs...

[hgs_notes]

Something to check, at the ignition switch plug, the large pink (or faded red) wire is the main power. I have one that had a new spade terminal put on the wire, but it doesn't seat like the original, so when it's loose, I have to push it in for a better connection. When it's loose there is no power to the starter. Sometimes it slips right out completely. So check those connections out. Mine had no splices either, but found that little problem. I also forgot to plug in the neutral safety switch to complicate things further.

[Musclerodz]

Did you order the correct dash harness? Was the truck originally a manual and converted to auto? The neutral saftey switch is in different locations and may not be letting power get to the starter.

[bouncytruck]

The truck was originally a 307/3 speed column shifter. Musclerodz may be on to something. What do you have the purple/lightblue wire connected to in the wire harness?

[lks dcvn]

hgs_notes - didn't see any issues with the pink wire to the ignition switch on either harness...

As Bouncy mentioned the truck was a manual changed to an auto - I didn't buy the harness from a vendor/store...I got an uncut (non-spliced), full gauge dash harness from somebody on CL about a year ago and am I now getting around to trying to install it and clean up the dash wiring.

I couldn't see paying $$$ for a new harness from a vendor when I would have to cut/splice it for the B&M Hammer shifter stuff anyway.

Purple/light Blue wire is connected to the firewall connection - can't tell where it goes from there without removing the dash harness again...to see the back of the fuse block and trace the wire. Go figure. That gives me something to look at when I get home - one step at a time - I guess.

Anybody have a picture or know the difference between the AUTO and MANUAL dash harnesses - I can spot the diffs on the full guage cluster vs. idiot light ones pretty easy, but I don't know the Auto vs Manual changes.

Thanks for the help everybody - I can't tell you how much better I will feel once the truck's dash wiring is cleaned up - - AND the truck starts

[Musclerodz]

On a auto harness the NSS switch is on the column and fairly certain should not go through the firewall block. Is the harness out of the same year truck? The "new to you" wiring harness could have a burnt or bad wire somewhere as well.

[jaros44sr]

I would think that a manual wire harness wouldn't have any of the NSS wires in it, but GM may have included them in all the harness's, just for ease of assembly. just a guess...

[bouncytruck]

Can you turn the starter without the clutch engaged on a manual?

[70rs/ss]

I bet the NSS plug is there and it needs a jumper wire across it. If the harness is from an auto the plug will hang near the bottom of the colum and a standard the plug will be near the clutch peddle. The best way to do this (not easy, by any means!) Unplug old harness one plug at a time and plug in the plug from new harness, making note of a plug from old the new doesn't have or vica versa. It is a NSS or clutch release issue as there is no power to the starter, the hei isn't the focus, but there has to be a plug on the new harness where the old one has the wires spliced together, as there is an open circut from the switch to the starter. Try the one plug at a time and I am sure you'll find a plug, once you find the plug (NSS or Clutch release) it is a simple matter of cutting the plug out and splice the wires together, since the under hood harness has been rigged to operate the NSS for the floor shifter. Good luck, just be patient and alert, it is there, you just need to find it!!

[lks dcvn]

So much for an easy harness swap to clean up the wiring -

Thanks for the help everybody - I hope to get these issues wrapped up...and get the replacement harness installed soon.

Does anybody have a picture of an auto and a manual trans dash harness side by side to see the difference(s)?

[DANTES JIMMY]

i do not have any pics but i had a 3/4 ton with a manual and it "looked" identical i think 70rs is right they use the same wires for a nss or a clutch switch
the clutch switch is probably up around the dash cluster so i wouldnt be surprised if it weren't up high on the harness
i may be wrong but im thinking that a factory harness they are a bigger awg purple wire but dont hold me to it

[Yukon Jack]

Here are pics of the harnesses in my engine bay - these are for a manual tranny and are set up for an internally regulated alternator and I believe HEI style.

Here should be an old thread I started about these harnesses.

I believe the wires go to these things:

1 ground
2 ground
3 horn
4 headlights
5 front turn or side marker
6 front turn or side marker
7 alternator plug
8 also for the alternator alternator ?
9 ground maybe
10 junction block on fender
11 junction block on fender
12 front turn or side marker
12a front turn or side marker
13 headlights
14 ground
15 distributor
16 appears to be for the oil pressure idiot light
17 starter posts
18 transmission - back up lights
19 temp sending unit
20 master brake cylinder
21 appears to be for the TSC

[lks dcvn]

Thanks for posting that - I have 1/3 of those wires on my engine harness -

Here are 2 harnesses that I have - the one on the right is the one I was trying to swap in (purple wires) - the one on the left is another one I just picked up for spare wires/terminals...

The biggest difference that I see between the two is the addition of the purple wires on the harness...

[Musclerodz]

Those additional purple wires is the NSS switch hook up for the column. You could cut the connector and crimp them together to bypass the NSS but won't recommend it.

[lks dcvn]

any reason why the other one wouldn't have the purple(NSS) wires...

I realize that this stuff is likely 40+ years old...and anybody could have had their hand in it over the years...