Yes, those are the wires to check. And I do mean the diodes, capacitors, etc by "components". You have a good plan.

 

If the tachometer is good [?], then it would have to be in the wiring. Previously, some forum members who had a tachometer, but not the correct printed circuit for the dash, simply hardwired the tachometer. You could try that before replacing the tachometer. This would, in effect, bypass any faults in the truck's wiring harness. Keep in mind that the V8 requires grounding of two points on the factory tachometer.

 

My money is on a wiring fault, most likely in the signal wire from the coil. x2 on what Gary said about cold solder joints, also. The fact that it's so intermittent just screams wiring issue to me.

 

Alright everyone, things just got serious. I have documented my endeavors today on my tach repair. If you can figure out this mystery with the clear work and pictures I am going to upload, I would deeply appreciate it.







So I decided to replace the entire green wire that leads from the coil to the plug since the previous wire was burned slightly.





Here you can see my very nice shrink wrapped connections I made. I used 14 gauge oil and gas resistant insulated wire from home depot.





I decided to pick up some CRC contact cleaner from home depot while I was there. Worked rather well cleaning the connections.





These are the two connections that I cleaned.





I used some dielectric grease on the connections.





Heres the connections I applied the grease to.





Also most importantly added the grease to these connections.





Connections all plugged back up.





Got all the tools together to work on the instrument panel.





For everyone that is concerned, here is the circuit board.





After removing the tach, here are the connections that the tach connects to.





Nice picture of the PCB of the tach, you can see the areas that were scraped earlier to remove the gunk.





Everything seemed to be fine.





Another picture.





Yet another.





Here is the reverse side, checked for cold joints, did not see any.





Another picture.





Decided to clean off some gunk that may be under the components with some compressed air.





After a dusting, removed all the nasty gunk.





As you can see, everything seems to be in order.





No problems that I can see.





There was only this one section between the capacitor and resistor that was in question.





Another image of the PCB and the previous cleaning that took place.





everything seems to be in working order.





Looks good, about to put the cover back on the tach now.





Pulled out the rubbing alcohol to clean connections.





Cleaned the connections on the PCB for the tach.





Also cleaned the nuts that attach electrically to the PCB.





Put a thin layer of dielectric grease on the contacts.





Since the instrument panel was already out, I decided to paint the needles. I used some enamel paint for model cars in florescent orange.





The needles look really nice with the coat of enamel on them.





I cleaned the contacts and then put a thin layer of dielectric grease on the contacts.





As you can see, the tach worked after all that work, thank goodness.








*UPDATE* started the truck up later that night to go to the store and.... NO TACH!! ughhhh





Then this happens, the last photo was taken at 2129, and then this photo was taken at 2145. I am really at a loss here. It hasent died on me afterwards, I started the truck and cut it off 3-4 times after, and it stayed on, but who knows for how long. I wasent kidding when I said its the factory tach from hell. ughh I appreciate you all for helping me out with this.

 

I hate to tell you, but you used the wrong grease on the contacts. Here's what Wikipedia has to say about it:I use a copper-filled anti-seize compound for doing what you did on the contacts, but dielectric grease on the connectors. I realize Wikipedia says it can be used on contacts but I think it is specifically talking about spark plug connections where there is high pressure and low surface area. But the connection to the cluster is a low pressure/high surface area one and isn't the right thing to use there.

Also, when cleaning those connections and the ones under the nuts I like to use a pencil eraser. But you have to use it gently as the copper traces can be pulled loose. And that's where I really like the copper-filled anti-seize as it completes the circuit as prevents oxidation.

Edit: I forgot to say that I think some of those solder joints could be cold. But the pic wasn't focused in all areas so I really couldn't tell.

 

Good job on ridding the brown crud off the circuit board. Where the lugs attach to the PCB looks like a cold joint is forming. You see the solder flux is a ring around the posts , that is a weak joint there.
I would of re soldered the whole PCB while I had it out. It helps as there are cold joints forming that you do not see.

One way to find out if the tach is bad or a wiring is the issue is to hook up a aftermarket tach directly to the back side of the factory tach. With both tachs getting signal from the same wires, I quickly found my tach problem on my truck, the after market worked fine while the factory tach went nuts...

 

I agree that the lug solder joints look poor. And it won't hurt to re-solder everything.

 

I don't like the look of that solder joint on the blue wire to the tach face. x2 for resoldering the whole board, if you're comfortable doing that. Also, the hooking up of an aftermarket tach in parallel is a great idea, will definitely let you know if it's your tach head or not.

 

I have taken the advice given into consideration, soldering the entire board over again to include the posts. I have driven the truck the past couple days and I have noticed that the tach does not work in the cold morning, but if I run the heater the tach will click back on after 10 minutes or so. This has happpened multiple times, which makes me to believe it is most likely a problem at the PCB.

ALSO, I was wondering, is there any documentation out there for electrical schematics for the PCB of the tach?? Im sure its a long shot but does not hurt to ask.

In response to the grease complaint, I would like to quote someone in the field of electronics below.

From (Dielectric Grease vs Conductive Grease)

"The word dielectric is assumed to mean the connection will have future problems because "dielectrics" are insulators. Generally, authors predict greases with powdered metal (in slang "conductive greases") will improve or maintain connection quality over time while dielectric greases will isolate connections because "that is what dielectrics do". ///break/// I continue to use silicone dielectric grease today. I use it as a lubricant on coaxial connector O-rings and threads. I use it to lube stainless bolts and nuts, to prevent galling. I use it for plug-in connections, in particular in my automotive hobby. I also use silicone dielectric grease for battery terminal connection preservation, coating it directly on the battery post. I use it in liberal amounts on ground connections, to inhibit corrosion on stainless-to-zinc (galvanized), lead-to-lead, stainless-to-copper, and stainless-to-aluminum electrical connections. ///break/// I have never found a problem with silicone dielectric compound increasing resistance or increasing wear. We use it in new equipment production to lubricate and preserve contact plating in very low current meter switches."

Thank you everyone for the input, and I will have to purchase myself a soldering gun and solder to resolder the board later this weekend. I really appreciate everyone here, Thank you.

 

To each his own on the grease issue. But I seen no reason to re-do what you've done as the connections have obviously been made. On the other hand, I'll continue to use copper-filled anti-seize on my connections.

However, I do agree that you have a problem with the PCB or the associated solder joints. Expansion and contraction seem to be causing the disconnect.

Also, I'm not aware of any schematic for the tach.

 

That actually reminds me, my tach sometimes doesn't like to jump up when I start my engine on cold mornings. But I just tap on the instrument bezel or dash nice and hard and it jumps right up to 700 and operates normally. Haven't looked into it yet simply because I don't mind rapping on it to start it off. But you may try this to see if it makes yours engage. I'm eventually going to lubricate the needle pivot to see if that's the issue (which I suspect it is). Also, mine starts working as soon as the cab is warm as well, if I don't tap on it.

 

Thanks for the input theguruat12, I am going to give this a try before I start the lengthy process of re-soldering the entire PCB to see if that solves the problem, and I will keep everyone informed.

 

If you do lubricate it, you're going to want to use something that is unaffected by temperature, and will last a long time. Personally, I lubricate all of my speedo cables/head parts and the tachs pivots I find with graphite oil.

 

I have a schematic of the 80 to 86 tachs I found years ago, BUT I CANNOT edit and add any photos to my gallery! Just get a blank screen on edit functions.....

 

Can you email it to me? I'll PM you with my address.