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does anyone have a wiring diagram for the factory tach? my dash does not have one in it now and i want to add the instument cluster package that does but i cannot find a diagram.
 

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sorry i forgot this is an 86 with a 2.8L with a/c i have a factory wiring harness book from gm but it is an 1989 snd it does not have it in either and that doesn't make sense because i also have an 89 baja with the 4.3L and thst has a tach. i do not want to tear the 89 apart to install a tach in an 86.
 

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Goin' Nowhere Fast
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you got'er....one wire from the + of the coil, another wire to a constant power (tap into your radio wiring ;)...I just used my old DRL power sounce haha), ground and tap into your dash lights for a backlight and you is done like dinnah!
 

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He Who Rallies da Hardest
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Hi, new member here. I've searched the forums and can't find an answer to this.
I also have an '86 2.8 (Blazer, tho), and the other day I got an instrument cluster w/ a tach from the junkyard to replace my tach-less cluster.
When I went to install it, I noticed there's a seperate connector for the tach. I cannot for the life of me find this connector on my wiring harness.
My question is, specifically, does anyone know if the non-tach-equipped vehicles have a different harness on them that lacks this connector? I know I can run a wire to the coil, but I'm curious about this. If noone responds, my curiosity will force me to go back to the boneyard and see exactly what the deal is with the stock tach wiring....I'll then post my findings.
Anyone?
 

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He Who Rallies da Hardest
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Oh, and if I do end up having to run the wire myself, I need someone to clarify for me....on this thread, zoommed75 and 2.5FearFactory say to hook to the positive side of the coil, but on other threads I've heard to connect to the negative... Is it different for the factory tach? Also, which one of the four post on the coil is which? I've only installed a tach on a V8 HEI ignition before, and it has a spade terminal clearly labeled "TACH".

Thanks in advance.
 

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Uhh, guys, it's the negitive side of the coil, not the positive.
 

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He Who Rallies da Hardest
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Time for some CLOSURE on this tach wiring shyte.
I made it back to the Pull N' Save and scoped the factory tach wiring on the donor '86 Blazer. The tach plug hooks into main harness under the dash. I happened to have to remove the dash on my '87 to replace the damn heater core :rant: anyway, so I checked and it definately does not have this plug. So it's going to be necessary to go through the firewall to get a tach signal, for sure.

The nice thing is, I found out I'm not going to have to splice into the wire at the coil! :D ....And maybe you won't have to either! (I always prefer a non-intrusive method) Check it: On mine there's a connector hanging out of the wiring harness just to the passenger side of the brake booster. This is some sort of diagnostic connector, and can be used for a tach signal! I tried it on mine, and it works. I'm just going to cut off the goofy connector and butt-splice on with my wire to the tach.
(NOTE: They could just be discolored or something, but on my Blazer, the wire next to the fatty red wire in the connector on the coil appears to be yellow, as opposed to white, and the wire to the above-mentioned diagnostic plug appears to be pure white, as opposed to white with a black stripe.)

(Ya might check out THIS page on the subject)


Tach it up, tach it up, buddy gonna shut you down! :evilg:
 

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Ugg, the "fatty red" is pink, always has been the GM ignition colour (well since the late 60's anyway.

The "yellow" wire is white, just discoloured.

How is cutting that connector off, NOT intrusive, it's just the same as splicing into the connector at the coil. There is usually a spade connector at or near the coil, that is used for the tach connection, this is probably the same conector you are talking about. The factory tach wire passes through the firewall, to the passenger side of the brake booster, it is a single wire. Why they didn't just add it to the other harness(es) in the truck I don't know.

The tach wire has NEVER been a white with a black stripe, it has always been white only, I don't know why people will say w/ black stripe.
 

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He Who Rallies da Hardest
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The_Raven said:
Ugg, the "fatty red" is pink, always has been the GM ignition colour (well since the late 60's anyway.
Yeah, pink, my bad. :eek:

The_Raven said:
The "yellow" wire is white, just discoloured.
Aight, that makes sense.

The_Raven said:
How is cutting that connector off, NOT intrusive, it's just the same as splicing into the connector at the coil. There is usually a spade connector at or near the coil, that is used for the tach connection, this is probably the same conector you are talking about.
Okay, I guess I should have said I prefer a "less intrusive" method instead. I would much rather cut off and connect to an unused test connection than whack or splice into the coil-to-ignition module wire :dunno:......just my $.02.... I don't see a spade connector at or near my coil for tach, and I don't think the connector I was talking about is the same one you are talking about. This connector isn't by the coil, it's by the power brake booster, and from what I've read it's supposed to be used for diagnostic purposes....check out the link in my last post, that's where I found out about it from.
 

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rallyhard said:
Okay, I guess I should have said I prefer a "less intrusive" method instead. I would much rather cut off and connect to an unused test connection than whack or splice into the coil-to-ignition module wire :dunno:......just my $.02.... I don't see a spade connector at or near my coil for tach, and I don't think the connector I was talking about is the same one you are talking about. This connector isn't by the coil, it's by the power brake booster, and from what I've read it's supposed to be used for diagnostic purposes....check out the link in my last post, that's where I found out about it from.

Again, I just don't see the difference, both ways just as "intrusive" to me. BTW, I work with automotive electrical on a daily basis. ;)

That is most likely teh same connector I am talking about, sometimes they get moved from year to year, sometimes day to day, the harnesses are afterall, assembled by hand, which leaves a bit of room for error or difference between them.

It's not for diagnostic purposes, though it can be used for that, because it is afterall a tach wire.

I did check out that link, those posts are by people who have heard from a guy, who read in a book once, that was told that it might be that way. None of the people that posted in that threda have much hands on electrical experiance with vehilce, at least not in a proffessional basis.
 

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He Who Rallies da Hardest
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The_Raven said:
Again, I just don't see the difference, both ways just as "intrusive" to me. BTW, I work with automotive electrical on a daily basis. ;)
As much as I appreciate your opinion on whether this method of hooking up the tach is "the same" as hooking in right at the coil....oh wait, I don't. I just figured some people who were informed of this unused terminal would, like me, rather use that than have to put a splice into the wire at the coil or otherwise ghetto-rig a connection there. I would think that most people who work on auto electrical every day would agree... :dunno: Besides, this connector is easier to get to, and probably closer to where you'd want to go through the firewall. I only see advantages to doing it this way...

The_Raven said:
That is most likely teh same connector I am talking about, sometimes they get moved from year to year, sometimes day to day, the harnesses are afterall, assembled by hand, which leaves a bit of room for error or difference between them.
Well, from the thread I got the information on that connector from, it appears the connector was by the brake booster as early as '85 on trucks without a factory tach, and it's still there on my '87 without a factory tach. But if it is the same connector.....cool. :cool:

The_Raven said:
It's not for diagnostic purposes, though it can be used for that, because it is afterall a tach wire.
On trucks with a factory tach, the tach plug is wired into the harness under the dash, not hooked in under the hood....which leads me to believe that it's there for diagnostics, not put there specifically for hooking an aftermarket tach or something....

But whatev....that's irrelevant....I posted this info because I searched this forum and didn't see that anyone had pointed out this connector before, so I hope this info has helped some people hook up their tach in a way they like....

The End
 

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rallyhard said:
As much as I appreciate your opinion on whether this method of hooking up the tach is "the same" as hooking in right at the coil....oh wait, I don't. I just figured some people who were informed of this unused terminal would, like me, rather use that than have to put a splice into the wire at the coil or otherwise ghetto-rig a connection there. I would think that most people who work on auto electrical every day would agree... :dunno: Besides, this connector is easier to get to, and probably closer to where you'd want to go through the firewall. I only see advantages to doing it this way...

Well, from the thread I got the information on that connector from, it appears the connector was by the brake booster as early as '85 on trucks without a factory tach, and it's still there on my '87 without a factory tach. But if it is the same connector.....cool. :cool:

On trucks with a factory tach, the tach plug is wired into the harness under the dash, not hooked in under the hood....which leads me to believe that it's there for diagnostics, not put there specifically for hooking an aftermarket tach or something....

But whatev....that's irrelevant....I posted this info because I searched this forum and didn't see that anyone had pointed out this connector before, so I hope this info has helped some people hook up their tach in a way they like....

The End
HOLY ****, you're an idiot, no other way to say it.

Look under the hood of ANY factory tach equipped S-series, it IS connected at that plug. :roll:

Splicing ito either wire which BTW is the SAME wire, if you take the harness apart, is the same outcome. The way it owkrs is this:

The pink ignition lead comes from the firewall, attaches to the coil in this same plug (black IIRC), there is a white wire, this wire is the same wire at the brake booster, or by the coil, wear ever it happened to end up, that day as the person making put that connection.. The other plug on the coil then attachges to the dizzy, the pink wire in the jumper harness carries 12V to the ignition module in the base of the dizzy. The white wire is the signal from the ignition module to the coil to fire. Both white wires and both pink wires are internally connected in the coil. So wether you splic into the white wire AT the coil or cut off the connector, you end up with the SAME result, so there is no "less" intrusive method here, just connecting at a slightly different location along the wire. It's probably becayue I work with automotive electricall everyday that I understand there is no difference, and don't agree with you on the "less intrusive" idea that you have brought forth, becauyuse when you break it all down, it's not. :roll:

It's not FOR diagnostics, or connection of an "aftermarket" tach, but for teh factory tach. I'll have to look on my truck and see if I have cut that off or not when I did my engine swap, I'm using a VERY different top end and wire harness. I had originally left that factory plug on, but developed problems with the tach jumping or not reading, so I cut it off and used .250 spade terminals as replacments, but rest assured that connectionis for a factory t tach, no doubt about it, using it for diagnostics would be a secondary benefit, especially since the Diagnostic computers that GM uses and even used at the time, show RPM right on the screen through the ALDL port.

But I'm done with this, no one seems to want to use logic any more, and refuse to argure anymore with someone who is opposed to using logic.
 

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He Who Rallies da Hardest
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The_Raven said:
HOLY ****, you're an idiot, no other way to say it.
Hah, well you're obviously quite the :ahole:, but I'd say you've shown yourself to also be the one idiot here by pointlessly, repeatedly, posting to try to state some lame opinion of yours. My point is that hooking in to this connector is simply the best and easiest way to connect a tach to your non-factory-tach-equipped S-10! I'm still not sure what yours is....

Thanks for the spiel on how the wiring is laid out in these S-10 ignition systems, but I had already gathered all that from betterthanyou's link to the wiring diagram earlier in this thread.
You might be right about the factory tach hooking up to this connector; when I was inspecting the donor rig at the junkyard, I only followed the factory tach wiring to where it hooks into the main harness. I didn't know of the connector at the time I was checking. So if this is where the factory tach hooks up, then this makes me wonder why anybody would even consider going right past it to connect at the coil instead??? :dunno:


Now I wonder if you can follow your own advice and STFU so you don't make yourself look like even more of an :asshat:.... Looking at your previous posts, it appears you've made some actual contributions to this forum, and I've gotta give you credit for that, but your arrogant attitude and ineffective put-downs in this thread are doing nothing more than increasing your post count.

Have a nice day and happy Blazering, dickhead.
 

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weezle29 said:
does anyone have a wiring diagram for the factory tach? my dash does not have one in it now and i want to add the instument cluster package that does but i cannot find a diagram.
No diagram, but here's a pic of the factory tach wire & connector on my '87 (2.8/auto). The wire should be there whether or not the truck came with a factory tach:

http://www.icehouse.net/wirenut/tachwire.jpg
 

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I have some good info on this subject so I figured I'd revive this old and somewhat entertaining thread.
I picked up an instrument cluster with the factory tach from an '87 S10 Tahoe and I did some searching here for help on wiring it, but couldn't locate anything definite so I went back to the yard and pulled the tach wiring too. Here's what I learned:

The design of the wiring in these trucks is a plus, there seems to be a base wiring harness and then separate and smaller harnesses are added with the options. Meaning the tach wiring is not part of your main harness and the cruise control wiring is exactly the same, either or both options can be added without any intrusion into your factory harness. I'll document the cruise in another thread, but here's the scoop on the tach wiring:

This is the factory harness for the tach:

Yep, that's all there is to it. The plug to the tach and three leads off of it.

The brown wire plugs into the fuse box. I'll have to take a picture of the proper plug on the box and post it here later.
The white wire connects to the wire next to the brake booster.
The black wire is a ground. Proper placement is the ground strap behind the instrument panel on the L/S that provides ground hookups for various accessories.


Tach lead wire with rubber grommet for where it passes through fire wall:


Plug into back side of tach:



Factory tach lead:



I haven't studied mine too closely yet, but it looks like if you want to use the factory firewall grommets you'll have to cut some holes, it doesn't look like they are cut and plugged. The same for the factory cruise control. Again, I'll update as I perform the work.
 
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