I wish I'd have known how, and I would've. I'll pull the cluster tomorrow and test the tach as you said. (I'd do it today, but I won't have a chance to til late). I bought the cluster mainly for the trip meter speedo though, plus it was only $10, so even if this tach is a dud, I still have all my other gauges.

I made sure to be careful when I removed the cluster and took it home. I bumped it once or twice (enough to make the small gauge needles shake a bit) picking it up, but everything (except the tach) seems to be working properly.

I read in another topic about these tachs that sometimes there's factory glue on the connectors of the tach, and over the years, the glue dries out and becomes conductive, causing malfunctions. One member said that he'd fixed several tachs just by cleaning off the old glue and spraying the connections down with PC board cleaner.

EDIT: Just thought of something...on the tach side of the two-wired connection by the DS box, it has a little rubber piece on the face of it, with slots for the male connector's prongs to fit through. The rubber piece is attached pretty darn securely (I gave it a good tug with pliers, but it wasn't gonna come off unless I strong-armed it). Is this some sort of insulator to keep the tach signal from getting to the cluster on a non-tach vehicle? There's no such rubber piece on the DS box's connectors.

 

I have never tried to repair a tach, but I would take it apart before I would toss it out.
<O</O
I think the rubber is just a weather seal. Stab the green wire with a straight pin and hook your sunpro tach to the pin to see if there is a signal on both sides of the connector.

Jim<O</O

 

By connectors, I think he meant the little posts on the tach housing where the circuit film connects to it. I don't know about repairing tachs internally either.

Will do. I'll post back as soon as I find something out. I have to go to work now though, so it'll likely be this evening before I have an answer.

Thanks for all your help, it'll be cool if I can get the tach working.

 

According to my 1981 factory wiring wiring diagram:

Black/Light Green Dots goes to Black/Light Green on the coil;

Dark Green/Yellow Dots goes to Light Green on the coil.
OR (it'd depend on the exact harness installed on the application)
It can go to Light Green on the DS2 module.

Do you have a volt meter? Those two wires are also on the plug that gets plugged into
the back of the cluster, they're near one of the ends and both on the same side (right
next to the white/red stripe wire on the very end). You can unplug that connector and try
testing for voltage on both of those leads (I'd do it with the engine running), that would tell
you those wires at least have voltage and would reduce the chance that the wiring is to
blame.

As has already been suggested, you can try hooking up your aftrmarket tach to those
signal leads and see what you get.

 

I actually have a multimeter that measures AC, DC, and some other things. Will that work?

I'll do both tests in the morning, since it's pretty late here. As soon as I find something out I'll post here right away.

 

That (on a DC voltage measurement setting) should work just fine.

 

Cool. Any particular voltage range to look for, or am I just looking for any kind of voltage at all?

Would the IVR have any effect on the tach's operation? I read somewhere on here that the tach uses 12v, not the lower voltage that the other gauges use, so it supposedly doesn't get power from the IVR.

 

Quote:

Originally Posted by TheKirbyMan

Cool. Any particular voltage range to look for, or am I just looking for any kind of voltage at all?

I would be looking for something around 7-14V but I'll bet it's gonna be pulsing
really quickly and I suspect that'll make it read "low." I've honestly never
measured the voltage on those wires so my guess would be what I stated above.

Quote:

Originally Posted by TheKirbyMan

Would the IVR have any effect on the tach's operation? I read somewhere on here that the tach uses 12v, not the lower voltage that the other gauges use, so it supposedly doesn't get power from the IVR.

Right, the tach, ammeter & speedometer are independent of the rest of the
gauges; the IVR lowers the voltage to around 5V to the fuel, oil and temp
gauges, this is because the vehicle's electrical system voltage will vary from,
say, 10 to 14 volts depending on if the engine is running or not, the load on the
alternator, accessories turned on, stuff like that. This deviation could cause
those gauges to read higher or lower than they should, so they're brought
down to a common, lower voltage so the gauges shouldn't be affected by
normal voltage variations.

Hope I didn't tick ya off with my computer-luser response.

 

Alright. Up til now, I didn't even know a tach signal could be measured. :P

Interesting. And lol, I speak computer-luser on a daily basis. :P

 

The best way to test the tach wires would be to disconnect the horseshoe connector on the coil and the instrument cluster connector and check for continuity between the two connectors.

Set your multimeter to ohms. Zero out the dial, then measure continuity between the two ends of the same wire. You should have a voltage loss of zero ohms on the wire. You may need to get longer leads for your tester.

This checks if the wiring is good only, but can take some guesswork out of the varying voltage levels the coil tach lead would produce due to pulsation.

 

Ok I'm back. Sorry for the long wait, it's been a busy, busy day.

I pulled the cluster today, started the engine and tested for voltage on the green/yellow dotted wire and the black wire directly next to it to the left (top side of connector). I got a reading of ~6.5 volts, with rapid fluctuations between 6 and about 6.60.

This leads me to believe that the tach is the problem, not the wiring. I even removed the little spring-metal nuts on the back of the tach and used a screwdriver to sort of rough up the contact area in hopes that it'd allow for better contact. No such luck. The tach still doesn't respond. I'd think that it'd at least move a little bit when I turn the key on.

What color is the wire(s) that bring power to the tach for its B connection? I'm curious as to whether it's possible that it's just not getting power somehow.

Since I've got coil voltage at the cluster connector, do I still need to check for continuity?

 

I wouldnt check continuity as you have a tach signal present.

Put the voltmeter directly on the metal studs/spring nuts to test for 12 volts at B
You could check for the tach signal again at the stud/spring nut also to be sure it is not the paper circuit film.

Jim

 

Alright. Just wanted to ask.

Do I put the ground lead on my meter to the G post on the tach or to a different ground?

Also, when checking for tach signal at the tach itself, where would I ground my meter to?


I'm likely going to be swapping out my IVR today or tomorrow...my gas gauge has been acting up. It tends to read lower, not higher though. My oil pressure gauge is the opposite, it tends to read high.

There's times the gas gauge needle will wiggle side to side really fast like it's being vibrated. I got the same sort of "vibration" on the temp gauge needle a time or two, but that gauge stays bottomed out since it's not hooked up to a temp sender. On top of that, my oil gauge tends to go up toward the L in normal, when the original cluster's oil gauge would maybe get to the M at most. Sure it's a little cold today and I run 15W40 Rotella, but that's not going to make me run 60-70PSI oil pressure at close to operating temperature....

 

I would use the G post as this will also test the ground wire for the whole cluster. If the whole cluster had a bad ground it would effect ALL the gauges.
You should get 12 volt with the meter across the G and B post, if you dont move the ground and try again. Same for the tach.

Also before you buy an IVR, test the ground with the meter on OHMs. With one lead the meter connected to the G post and the other lead touching a good clean ground point (metal) you should get a low number, or the same as touching the leads together. with the meter still hooked up, wiggle and shake the wires a little.

Wait.... didnt the replacement inst cluster have an IVR on it, have you tried this one out yet to see if the gas gauge needle wiggles????

Jim

 

Will do. I'll probably check that tomorrow, since I won't be able to get around to it til late tonight, like last time. As soon as I find something out I'll let ya'll know.

I put in a different, complete cluster, gauges and all. The only parts I used from my original cluster are the twist-lock bulb sockets. My original cluster does have an IVR on it though, and in the entire time I've had my truck, it's never once acted up like this. So I'll be trying the original IVR.

This stuff actually first caught my attention when I'd just be driving, say on a bumpy road, or a slanted parking lot for a short distance then going back to level ground, it'd take a while to get a correct reading. It'd read lower than what it previous did. Maybe the gauges vary from truck to truck, but this gas gauge's needle, when turned off, goes pretty doggone far to the left, considerably more than my original cluster's gas gauge.

If it's any consolation, at least the ammeter works. lol. Dunno if it's accurate, but it moves. lol