Sun Tach Problem

[72-SS-L48]

Hi Guys,

The Sun tach in the 69 Z was not accurate so I pulled it out today. Since I did not want the tach wires to dangle, I installed another Sun Tach I had. It's the same model number and NOS perfect. It did not work in the car. I swapped that one for another and that didn't work either. Finally, I put the original tach that I removed back in it to see if that worked. NOTHING! What did I do? What happened that no Sun Tachs will work? I did not alter the wiring.

Thanks,
Dave

[VintageMusclecar]

Are these tachs stand-alone units or do they use transmitter boxes?

[72-SS-L48]

None require senders.

Thanks,
Dave

[VintageMusclecar]

How do you have the tach wired?

[Plowman]

That I think is a points tach. If a elt ign,or MSD,you will need a part on the white wire. Hope that helps. Check points and condenser too. Paul

[72-SS-L48]

The car has its original ignition system. The tach is wired with three wires.

One wire as the ground, one going to the coil and one plugging into the fuse box.

Mind you the tach worked when I pulled the car out of the garage, I went to swap tachs and nothing!

-Dave

[VintageMusclecar]

Start with the basics--check the wires for breaks and make sure you're still getting power to the tach from the fuse box.

[72-SS-L48]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: VintageMusclecar</div><div class="ubbcode-body">Start with the basics--check the wires for breaks and make sure you're still getting power to the tach from the fuse box. </div></div>

Didn't see any breaks. Wires look good (brand new). I'll hook a test light up to the wire from the fuse box tonight and see what happens. Should there be power from the fuse box at all times (with the battery connected) or does it need to be in the &quot;on&quot; position or car running?

Thanks Eric!

Dave

[VintageMusclecar]

Key on (ignition) only.

[njsteve]

Sounds like the wire broke at a terminal. Cut all the terminals off and install new ones. A lot of times the wire will break but the insulation will still hold it in place in the crimped-on terminal, making it look like a good connection.

[72-SS-L48]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: njsteve</div><div class="ubbcode-body">Sounds like the wire broke at a terminal. Cut all the terminals off and install new ones. A lot of times the wire will break but the insulation will still hold it in place in the crimped-on terminal, making it look like a good connection. </div></div>

That's a great suggestion. Thanks Steve.

Tonight I'll play around with it and see what happens.

-Dave

If my feeble old memory serves me correctly, the fuse box wire should be for the tach light only....so it should be clipped into that particular circuit.

Wayne

[VintageMusclecar]

Just noticed you said the tach has 3 wires--shouldn't there be 4?

If memory serves, there should be a black for ground, a white for light, a green that goes to the coil, and a red for power.

[x Baldwin Motion]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 72-SS-L48</div><div class="ubbcode-body">The car has its original ignition system. The tach is wired with three wires.

One wire as the ground, one going to the coil and one plugging into the fuse box.

Mind you the tach worked when I pulled the car out of the garage, I went to swap tachs and nothing!

-Dave </div></div>

a forth wire would be for lighting the tach face, spliced into dash light circuit.

[Plowman]

Some times the light circut is wired to the switch ignition circuit,so when the tach is on the face light is on. Try that[only 3 wires]. Paul

[72-SS-L48]

The wires are as follows.

Black that goes grounds to a metal support under the dash
Red that clips into the fuse box (power)
Green that goes to the coil
And the light wire that also clips into the fuse box (mind you the light does work, even with the tach not working)

Thanks,
Dave

[mockingbird812]

Which side of the coil are you tapping into?

[72-SS-L48]

The Green wire from the tach is going to the negative on the coil. I hit my power probe on the red wire from the fuse box and it has 11.6 volts.

Thoughts?

Dave

[72-SS-L48]

All connections are new and look good. I didn't replace any. How do you test the green wire from the coil? I know the coil is good since the car starts.

-Dave

[Plowman]

A quick way to check the green wire is with a test light and tapping the engine over a time or two. Test light should go on and off[not runing]. Not all coils are good since the car starts,some bad coils run out of spark and give a feeling like running out of gas. Could try another known good coil. The green wire should be on the negative side of the coil witch is also the distributor side. Hope this helps. Paul

[72-SS-L48]

The green wire makes the connectivity test light up when I tip the key. Still no tach works...

-Dave

[Plowman]

The test light should go on and off[not runing]. The tach works off distribtor pulses. Make sure it is on and off test light at distribtor wire[not runing]. Paul

[SuperNovaSS]

How are you hooking it up? Red: 12v switched power, white: light, black: ground, green: Neg. Side of coil?

Jason

[SuperNovaSS]

Oops, missed a page. I would bench test the tach and go from there.


Jason

[72-SS-L48]

Guys,

I hooked up one of my 8k tachs to bench test it. The tach does not work. It looks like I will send that one and my 10k back to D and M Restorations and see what they say. It's under warranty, I just do not know what caused them to fail...

Thanks,
Dave

[njsteve]

Have you checked the running voltage and the cranking voltage at the coil neg terminal? When i had the defective wiring harness that was missing the resistor wire, it put out way too much voltage when running and burned out the factory tachometer (14 volts when running). There should be 12 volts when cranking and 9 volts when running.

Make sure you're not just chasing a symptom instead of fixing the problem.

[SuperNovaSS]

The strange thing is you had a working tach that is now not working. It sounds like lines got crossed somewhere and all the tachs were fried as a result.


Jason

[72-SS-L48]

Guys,

I installed my last NOS unit in the Camaro. This one worked like a charm. I'm thinking my other NOS unit flat out does not work and maybe in swapping the two rebuild units two wires touched? I still do not understand how this happened since the battery was disconnected during the swaps but anyhow...

The rebuilt tachs have warranty's so they will be working in no time.

I appreciate everyone's help!

Dave

[Salvatore]

Trial and error. Its what makes this hobby fun or I should say rewarding.