new tachometer problems

[Kenneth Cole]

Hi
I installed a tach today and have a problem. This is the 3500 RPM tach with the terminal strip on the back. Anyway when I switch the ignition switch to run the tach will bounce up to about 1500 RPM and drop to zero right away and when I start the engine it sometimes will run up some RPM's and then just drop to zero.
I have checked my connections and don't seem to find any problems.

Any idea's?
Thanks
Ken

 

[doghead]

Contact the seller?

 

[NormB]

Someone with an EE degree can correct me here (not an EE, but a Ham and I've tinkered with some electronic projects in the past), but I think adding something like a 100 microfarad 50 volt electrolytic capacitor across the voltage screws (+/-) can smooth some of that out a bit by attenuating the voltage spikes.

Do a web search (I use duckduckgo) for "dc voltage spike capacitor" and look at the IMAGES. You'll see what I'm talking about.

More complicated would be a MOV (Metal Oxide Varistor) for the same reason.

I have some of that too, but ignore it as the wiring was done right and the tach works fine otherwise.

Norm

 

[1 Patriot-of-many]

Where is your wiring going, Pics would be good.

 

[juanprado]

the tach drive for the ste can fail and has been an issue for others assuming you are picking up signal from those 2 wires?

86humv has some I believe from a previous post.

 

[Kenneth Cole]

Juanprado

the tach drive for the ste can fail and has been an issue for others assuming you are picking up signal from those 2 wires?

86humv has some I believe from a previous post.

I read 86humv's post's on this and it sounds like that is my problem also. I will check to make sure everything is wired right and that I am getting power and a good ground before I order a new sender.

Thanks all for the inputs.
Ken

 

[Kenneth Cole]

Hi
Well I got a new sender and it still will not work. When I turn on the ignition switch the pointer pounces up and then back to zero. My thinking is that I am getting power to the tach but for some reason the signal is not getting to the tach or whatever. I have hooked up a meter to the sender and rotated it and do see an a reading on the ohm meter.

Anyone have any ideas?
Thanks
Ken

 

[Kenneth Cole]

Tach still dosn't work

Hi
So I got a tach and It didn't work. On a previous post we thought it could be the sender so I got a new one and that didn't help. Just like before when I turn the switch to run the tach needle jumps to about one grand and then back to zero. It's like I'm not getting a signal to the tach. I hooked up an ohm meter to the sender and rotated it and do get a reading. Not sure what to try next. Have any ideas?
Thanks
Ken

 

[Suprman]

You can try and drive it off the alternator ac output.

 

[doghead]

Please continue an existing thread, rather than start a new one to continue with the same issue.

I'll merge them now.

 

[NormB]

Hi
Well I got a new sender and it still will not work. When I turn on the ignition switch the pointer pounces up and then back to zero. My thinking is that I am getting power to the tach but for some reason the signal is not getting to the tach or whatever. I have hooked up a meter to the sender and rotated it and do see an a reading on the ohm meter.
Anyone have any ideas?
Thanks
Ken

My sender was toast. Before buttoning everything up, I ran 24 jumpers to the tach, and jumpers from the plug-end of the new sender. TNriverjet was kind enough to send another tach on the suspicion mine may have been faulty - it wasn’t - I offered to send it back, he asked me to “pay it forward” so I gave it to another member who paid postage.

Think simple.

Your tach’s getting voltage, that’s where the spike comes in (you could probably damp this with a 100 mfd 50 volt electrolytic capacitor if it bothered you enough), the sensing side gets an induced current from the sender. I tried measuring the resistance from it and there was no reading. Tried detecting any voltage - nada. I think it’s in microvolts, my Fluke VOM wouldn’t pick it up. Since I didn’t have a shunt handy to measure current, I didn’t, but it’s probably in millliamps or less.

So, power to tach, good.

”signal” from sender, good.

what wiring harness are you using? And what kind of connections are made?

I used some kind of 3M wire taps that connect to blade connectors, but try putting a pin into the rubber molded connector on the sender first and see if the tach works.

Only thing left is your wiring harness.

Good luck.

 

[Kenneth Cole]

Hi
The tach that I have is the one with the terminal stip. I used spade terminals with 18 gauge wire. I attached the power lead to the fuel gauge power wire and the ground to the ground screw on the instrument panel. The two wires to the sender, I stripped the insulation off of the wire and attached them at that point.
Ken

 

[NormB]

Hi
The tach that I have is the one with the terminal stip. I used spade terminals with 18 gauge wire. I attached the power lead to the fuel gauge power wire and the ground to the ground screw on the instrument panel. The two wires to the sender, I stripped the insulation off of the wire and attached them at that point.
Ken

Two possibilities come to mind.

1 - is the sender drive off the block working? Does is spin when the engine's running? Not 100% sure how you'd test this, but I don't think oil's going to spray out under pressure if you run the engine without the sender connected.

2 - something's wrong with the sender.

oh, and,

3 - the tach's dead.

If you had something like and old-fashioned battery-operated hand-held fan with a permanent magnet motor you could gut for the motor, or could just connect the motor to the tach and turn the fan that might work too to tell if the tach's broken. If this is your second tach, maybe the sender's not working.

Did you take readings off it with the engine running? I actually got some minor resistance changes this way, but no voltage.

 

[86humv]

You can pull tach drive...hook up the wires...2 to voltage, other 2 to tach drive...attach drill to sender tang and spin it.

 

[NormB]

You can pull tach drive...hook up the wires...2 to voltage, other 2 to tach drive...attach drill to sender tang and spin it.

Bench testing (indoors, warm/dry, good lighting) with a 24V source and drill hooked up like you said.

Great idea.

 

[LouWon]

I guess that i can also add to to the confusion, I also bought one a few months ago, finally decided decided to install it a few weeks ago, followed the instructions and hook up everything, turn the key on and I have a tachometer that works. But.... after driving around for about an hour, it cuts out, light is on, but no tach, so since I had bought the tach a while ago, I decided that the unit was defective and ordered a new one, the box came in still sealed, installed it and I was up & running again, but to my surprise after about an hour , the new one also cuts out, let it sit for a few hours or overnight, the tach works fine, but again after about an hour, it cut's out again.
Any clues, anyone ??

 

[1 Patriot-of-many]

Hi
The tach that I have is the one with the terminal stip. I used spade terminals with 18 gauge wire. I attached the power lead to the fuel gauge power wire and the ground to the ground screw on the instrument panel. The two wires to the sender, I stripped the insulation off of the wire and attached them at that point.
Ken

There are two power leads. One coming out the top with a black negative ground wire and another from the bus bar, one is for the light in the tach, the other for power to the tach. Pictures of where your wires are going would help. One of the power wires needs to go to the panel lights circuit and the other to something like the fuel gauge that is powered only when the ignition is on. https://www.steelsoldiers.com/showthread.php?153495-hmmwv-tachometer



It's a little confusing because in the first picture he has a red wire on the bus bar and then it's suddenly brown where it connects to the dash


I used Y connectors and bulk connectors for the the two power leads, looks more professional than the wire crimps to the sender. Post #7 on this thread https://www.steelsoldiers.com/showthread.php?170674-HMMWV-Lights-Which-wire-to-tap-into


WTH, How do I stop the hyperlink when editing a post?

 

[LouWon]

That is the exact installation I did and followed the instruction.
Like I said it works fine , but goes off after 45 min to an hour drive.
I will bring it in the shop and re-check everything, it's a weird problem

The only thing I did differently is to hook up the light and tach to the same feed, so the light is always once you start the vehicle

Thank you

 

[1 Patriot-of-many]

That is the exact installation I did and followed the instruction.
Like I said it works fine , but goes off after 45 min to an hour drive.
I will bring it in the shop and re-check everything, it's a weird problem

The only thing I did differently is to hook up the light and tach to the same feed, so the light is always once you start the vehicle

Thank you

I'd recheck all the crimp connectors, they basically suck but it's pretty much all we have here unless you want to add shell connectors and a Y at both leads off the sensor. Just for ^&*%ts and giggles try wiring up the positives up separately as in the link. I used Y connectors and bulkhead connectors at both positive leads to the instrument panels but didn't at the sending unit.

 

[LouWon]

Yes, that's what I had planned on doing
I do have good crimp connectors and i also have the good shrink wrap with glue
I will separate the light and tach feed, maybe it's that kind of a stupid problem or installer error, live and learn LOL