Adding Tach and not working after 2 new ones

[svastano]

So group I bought a tachometer from Tom's about 4 years ago and just got around to installing it last weekend. Got it all wired up and absolutely nothing from the needle but the light works when turned on with the headlights. So I called Tom's and they send me another one. Well last night switched them out and now when I turn the key on the needle cycles to full and back to zero, Start the bronco and the needle cycles again but I don't get any movement at all. Tom's is trying to help but didn't have an answer for me. So details: 77 Bronco with OEM ignition system, the box has a blue end coming out of it. Coil has been changed and it is a Accel chrome one. Signal is wired to the negative of the coil. I have checked ground and it seems good. I have good continuity there. When running the signal shows just under 11 Volts DC If I switch it to AC I get somewhere around 5 V. the Hot coming from the ignition is 14V when running. Any ideas what I have wrong?

 

[JB Fab]

Wow! 4 years and sent you a new one? That's bitchin' customer service!

 

[svastano]

They have been very helpful but getting this to work is not highest on the list.

 

[svastano]

I have been contemplating this since I wrote it yesterday. I was going to add a 2nd ground strait to the block and see if that makes any difference

 

[gnpenning]

I have been contemplating this since I wrote it yesterday. I was going to add a 2nd ground strait to the block and see if that makes any difference

Take the ground direct to the battery for testing.

 

[knack]

Have you tried connecting to the positive side of the coil?

 

[Johnnyb]

So there should be a ground and a signal wire. The negative side of the coil is intermittently grounded by the points/module. The ground (usually black) can be connected to the metal dashboard (bare metal) as that is a ground on an EB. The signal wire (usually blue or green) should be connected to the negative side of the coil. DO NOT connect signal to positive side of coil.

Disconnect coil and verify wires with voltmeter both sides. When disconnected, + side should show 11+ volts, signal side should show 0. It is important to disconnect because if you happen to catch it when the points/module are closed, signal side will show volts as well, that's why you aren't supposed to sit with the engine off in "run" position on the switch.

-JB

 

[svastano]

So I tried to ground it directly to the motor and no change. I didn’t have time to check the voltage on the coil yet.

 

[m_m70]

how many wires coming out and what colors? I have the same tach (I think). I'll try to take a look. I think mine has two grounds but it's been around 15+ years........

 

[Brush Hog]

Do you have the correct engine cylinders selected on the tach? I have toms tach about 2 years old and it has a selector switch for 6 or 8 cylinders. Not sure what happens if wrong one is selected but worth checking.

 

[svastano]

how many wires coming out and what colors? I have the same tach (I think). I'll try to take a look. I think mine has two grounds but it's been around 15+ years........

The Tach has 3 studs coming out. “I”. Ignition. “G”. Ground. And. “S”. Signal. And that’s exactly what I hooked them up to. Ignition is hot only when key is on. Signal is hooked up to negative on the coil and ground is hooked to the ground on my dash

 

[svastano]

Do you have the correct engine cylinders selected on the tach? I have toms tach about 2 years old and it has a selector switch for 6 or 8 cylinders. Not sure what happens if wrong one is selected but worth checking.

Yes. 8 cylinder is selected. I know that if you have the wrong one selected it will just show the wrong RPM. I have done that in the past

 

[svastano]

So the saga continues, I have done all the tests above and have voltage on the signal wire to the tach. I just haven't been able to verify with another tach. I am about ready to just go buy a tach at an auto parts store and use that to test my wiring etc. Matt at Toms has been super helpful but without another tach to test we are kinda dead in the water. I have a buddy that has one I just have not had time to get to his place so we can test.

 

[Johnnyb]

So the saga continues, I have done all the tests above and have voltage on the signal wire to the tach. I just haven't been able to verify with another tach. I am about ready to just go buy a tach at an auto parts store and use that to test my wiring etc. Matt at Toms has been super helpful but without another tach to test we are kinda dead in the water. I have a buddy that has one I just have not had time to get to his place so we can test.

My thought is that you probably should not have voltage on the signal wire as it is an intermittent ground signal. At the very least it should alternate between having voltage when the points/module are NOT calling for spark and ground when the points/module ARE calling for spark.

-JB

 

[svastano]

My thought is that you probably should not have voltage on the signal wire as it is an intermittent ground signal. At the very least it should alternate between having voltage when the points/module are NOT calling for spark and ground when the points/module ARE calling for spark.

-JB

I am only getting volts when the Bronco is running.

 

[svastano]

So the saga continues.... I got a known working tach from my buddy and tried wiring it direct to Negative on the coil ( Green wire) Red to positive on the battery and Black to negative on the battery, The tach cycles when I add power but I get nothing. Only difference I have on my 77 from stock is that I have an aftermarket Accel chrome coil, Any help advice appreciated.

 

[gnpenning]

Do you have a wire for the light?

I might have to go look at the wiring on my bronco. Motor is out though.

 

[m_m70]

I am only getting volts when the Bronco is running.

is the voltage pulsating or constant?? Assuming you check it with a multimeter.

I got a known working tach from my buddy and tried wiring it direct to Negative on the coil ( Green wire) Red to positive on the battery and Black to negative on the battery

I would be checking my wires at this point. Not a whole lot of things to go wrong here.

I would take your tach to your buddys and wire it up just like you're doing in your Bronco (but connected to his engine) with "your wires" and see what happens.

 

[svastano]

So I finally figured this out last night. I found this wiring diagram and then started checking wires.... Well the wires that were going to the coil were reversed, Green was attached to the positive terminal and Red to the negative. Bronce ran just fine like this but tach didn't work. I switched the wires to the correct positions and tach works perfectly!

 

[Shimmy]

Did ya have a celebratory beer yet?