Tachometer Hookup Help - New Cluster!

[1972BlueC20]

Hi guys,

I need some confirmation on how to hook up the tachometer on my new reproduction cluster I just got in the mail today.

I already know (thanks to TBONE1964, VetteVet and ray_mcavoy) how to change the positions of the wires in the cluster plug to convert from idiot lights to gauges, and I know about running new wires from the # 1 (to alternator) and the # 12 (to the junction block) with 4 amp inline fuses on both of these new wires.

The only thing that is stumping me at this point are exactly how to hook up the tach, I just want to verify one last time before I do all this that what I have read and been told is correct and that I understood it correctly from those who were so kind to help me!

Here are pics of my new cluster (front and back) and a pic that I drew lines onto of how I think I can run the wires for the tach since I have HEI....also a picture of the tach harness that came with the cluster. I don't think I need this harness since it appears to be for a points style distributor and I have HEI.

I also have a tach filter, some say I should use it, others say I don't need it....if I do use it, how would it be wired into this equation? I read the instructions but I'm still not 100% sure how to hook it up.

Lastly, does the tach have it's own light inside or does the 2 lights on either side of the tach illuminate the tach itself??

[1972BlueC20]

and picture of the tach filter

[1972BlueC20]

picture VetteVet gave me

[hdff]

sweet lookin cluster. if ya can't get it figured out we can put it in my truck, I need a new one and it would be plug and play... lol

other that I think the one wire from the hei to the tack is right, I can't be of any more help...

[1972BlueC20]

Can anyone help on this?

I don't want to fry my new cluster hooking it up wrong

[1972BlueC20]

Hi guys

Surely someone has done this swap before and can help me

anyone?

[ray_mcavoy]

Originally Posted by 1972BlueC20

... and a pic that I drew lines onto of how I think I can run the wires for the tach since I have HEI

Yes, the way you have it drawn in that pic would work.

Originally Posted by 1972BlueC20

....also a picture of the tach harness that came with the cluster. I don't think I need this harness since it appears to be for a points style distributor and I have HEI.

Yes, that harness does appear to be for a stock points distributor. However, you could still use it with HEI by simply cutting the forked terminal off the end of the brown wire and replacing it with an HEI tach connector like this:

http://www.repairconnector.com/produ...Connector.html

Originally Posted by 1972BlueC20

I also have a tach filter, some say I should use it, others say I don't need it....if I do use it, how would it be wired into this equation? I read the instructions but I'm still not 100% sure how to hook it up.

If you use that filter, you'll want to make the following connections:

(1) Black wire to a good ground.
(2) Yellow wire to the "coil" terminal on your tachometer. If you locate the filter in the engine compartment, you could spice the filter's yellow wire to the tach harness' brown wire.
(3) Red wire to HEI "TACH" terminal. This connection can be made using an HEI tach connector like I posted above.

Originally Posted by 1972BlueC20

Lastly, does the tach have it's own light inside or does the 2 lights on either side of the tach illuminate the tach itself??

Illumination is provided by the 2 lights in the cluster on either side of the tach. So there are no separate lights to hook up.

[1972BlueC20]

Thank you so much Ray!!

This helps greatly now I can proceed.

Do you think I need the tach filter?

If I don't use it, do I risk frying the tach?

[ray_mcavoy]

You're welcome!

I don't think there is much risk of frying the tach by not using the filter. The filter basically just blocks higher frequency "noise" from the signal that could potentially cause erratic / jumpy tach readings and / or interfere with radio reception. But since you already have the filter, you might as well go ahead and use it to ensure a nice clean signal to the tach.

[1972BlueC20]

Ok, I got the back of the cluster all prepped to install with a tach filter in the equation just for good measure.

Picture is down below.

Everything is soldered and tight and taped and crimped.

Let me know if everything looks good.

The red wire with the spade connection on the far left side will connect to another wire that will run through the firewall and hook to the HEI tach input.

I've already got my new # 1 and # 12 wires ran from where they need to be with 4 amp inline fuses, ran through the firewall just need to connect them to the proper spots on the cluster plug. After that I just need to swap around the cluster plug wires from their original positions (idiot lights) to the new positions (gauges) and I should be good to go.

Otherwise I have to hook up the oil line, which I also have ran through the firewall ready to hook into the back of the oil pressure gauge. I also still need to connect to it where the oil sending unit is now. Line is copper and coiled to prevent buzzing (so I've been told)

I will also add one more ground wire from the back plate on the cluster to a bare metal spot just above the parking brake on the bottom of the dash.

Should I have everything taken care of??

[HIGHWAY BY THE SEA]

Where did you get the tach filter? I need one of those before I hook up my tach.

[1972BlueC20]

Originally Posted by HIGHWAY BY THE SEA

Where did you get the tach filter? I need one of those before I hook up my tach.

http://www.classicparts.com/1947-72-.../#.VxoUPjArLcs

[1972BlueC20]

For the new wires I will be adding to the cluster plug (#1 and #12) I know I can use the old blue wire(s) bow terminal (blue wire = old oil sending unit wire) but will there be another un-used wire in the cluster plug that I can steal the terminal from for the other added wire??

I'm talking about these terminals...

[1972BlueC20]

Am I correct that when transferring from idiot lights to cluster I will no longer need to use the dark blue wire (oil sending unit) and the brown wire (generator) ?

I'm hoping so, because I need 2 bow type terminals for the new wires I have to add for # 1 and # 12.

I for sure know I have 1 terminal I can use from the oil sending unit wire, but I will be one short unless I can use the dark brown wire that is marked generator.

Please confirm if you have time!!


You can buy these terminals from Classic Industries, but they are like $25 for a small pack with shipping and I really wanted to finish my cluster conversion tonight.


Thanks!
__________________

[ray_mcavoy]

Originally Posted by 1972BlueC20

Am I correct that when transferring from idiot lights to cluster I will no longer need to use the dark blue wire (oil sending unit) and the brown wire (generator) ?

I'm hoping so, because I need 2 bow type terminals for the new wires I have to add for # 1 and # 12.

I for sure know I have 1 terminal I can use from the oil sending unit wire, but I will be one short unless I can use the dark brown wire that is marked generator.

Please confirm if you have time!!

Yes, the dark blue (oil light) and brown (generator light) wires are no longer used with the gauge cluster so you can save those terminals and re-use them for the #1 & #12 ammeter wires.

When it comes to re-using the terminals, I have in the past tried prying open the crimps and re-crimping them onto new wires but that is rather difficult to do without damaging the terminals. A better approach would be to simply leave a couple inches or so of wire attached to the terminals when you cut them off the dark blue & brown wires. That should give you enough length to splice them to the new wires.

Also be aware that the other end of the brown wire will still be connected to the alternator / voltage regulator. So insulate the cut end with some electrical tape or heat shrink tubing so it can't touch anything under the dash and create a short circuit.

[1972BlueC20]

Originally Posted by ray_mcavoy

Yes, the dark blue (oil light) and brown (generator light) wires are no longer used with the gauge cluster so you can save those terminals and re-use them for the #1 & #12 ammeter wires.

When it comes to re-using the terminals, I have in the past tried prying open the crimps and re-crimping them onto new wires but that is rather difficult to do without damaging the terminals. A better approach would be to simply leave a couple inches or so of wire attached to the terminals when you cut them off the dark blue & brown wires. That should give you enough length to splice them to the new wires.

Also be aware that the other end of the brown wire will still be connected to the alternator / voltage regulator. So insulate the cut end with some electrical tape or heat shrink tubing so it can't touch anything under the dash and create a short circuit.

Pewww....I'm so happy to hear this. This is exactly what I did. I took a chance and did this while waiting for a response from someone lol. Thx so much for all your help!!

Only thing left to do is to remove my old oil sending unit, and install the copper oil line in its place. Then hook it up on the gauge side as well.

I replaced my old dash pad while I was in there what a PITA !! Thankfully someone had left off the middle bolts near the radio. It was an original pad. A small quality control paper fell out dated 1971 when I pulled the old pad off.

Should have everything buttoned up today. Really hoping everything works as it should.

Also noticed recently a burning wire smell in the engine compartment before I started this cluster conversion. The fuse able link near the battery seems to be eminating this smell. What does this mean? I don't have any special non factory accessories. Just a custom auto sound head unit but not hooked to an amp. Recently replaced my alternator with the same one that had been in there for years.

What happens if my fuse able link goes out???

[ray_mcavoy]

Originally Posted by 1972BlueC20

Pewww....I'm so happy to hear this. This is exactly what I did. I took a chance and did this while waiting for a response from someone lol. Thx so much for all your help!!

You're welcome!

Originally Posted by 1972BlueC20

Also noticed recently a burning wire smell in the engine compartment before I started this cluster conversion. The fuse able link near the battery seems to be eminating this smell. What does this mean? I don't have any special non factory accessories. Just a custom auto sound head unit but not hooked to an amp. Recently replaced my alternator with the same one that had been in there for years.

That fusible link near the battery protects the main feed wire from burning up in the event of a short circuit or major overload. The fact that it's getting hot enough to give off a burning wire smell could be an indication of an overloaded main feed wire. But that's not very likely given that a Custom Autosound head unit is the only non-factory accessory in your truck.

A more likely cause would be a weak or corroded connection that is adding extra resistance to the circuit and causing the wire to heat up. So I'd recommend checking the junction block where the fusible link attaches to make sure it's free of corrosion, the ring terminal on the fusible link is in good condition and still crimped securely, and that the junction block nut is tight. The other end of the fusible link (where it attaches to the main feed wire) is usually pretty well insulated/sealed at the factory, but could still be subject to corrosion (especially since it is near the battery). Unfortunately, you'd have to cut away the factory plastic insulation cylinder to inspect that end. And it's possible that the fusible link wire itself has some internal corrosion that can't be seen due to it's insulation. If that is the case, you'd have to replace the fusible link. Use one that is the same size and close to the same length as the original.

Originally Posted by 1972BlueC20

What happens if my fuse able link goes out???

If it burns out, you will lose all battery power to the truck. If the engine happens to be running at the time, it will likely stay running off the alternator (provided the fusible link didn't blow due to a short circuit in the main feed wire). But if it's not running, you won't be able to start the engine if that fusible link is blown.

Also, with the addition of the gauge cluster, the main feed wire becomes a shunt for the ammeter (battery gauge). A blown fusible link leaves the shunt open circuit which has the potential to pass a damaging amount of current through the meter movement and it's wiring (the wires you are adding to the #1 & #12 spots). That is one of the reasons it is important to have the 4 amp inline fuses in those wires. They'll blow before enough current flows to damage the meter or wiring.

[1972BlueC20]

Originally Posted by ray_mcavoy

You're welcome!



That fusible link near the battery protects the main feed wire from burning up in the event of a short circuit or major overload. The fact that it's getting hot enough to give off a burning wire smell could be an indication of an overloaded main feed wire. But that's not very likely given that a Custom Autosound head unit is the only non-factory accessory in your truck.

A more likely cause would be a weak or corroded connection that is adding extra resistance to the circuit and causing the wire to heat up. So I'd recommend checking the junction block where the fusible link attaches to make sure it's free of corrosion, the ring terminal on the fusible link is in good condition and still crimped securely, and that the junction block nut is tight. The other end of the fusible link (where it attaches to the main feed wire) is usually pretty well insulated/sealed at the factory, but could still be subject to corrosion (especially since it is near the battery). Unfortunately, you'd have to cut away the factory plastic insulation cylinder to inspect that end. And it's possible that the fusible link wire itself has some internal corrosion that can't be seen due to it's insulation. If that is the case, you'd have to replace the fusible link. Use one that is the same size and close to the same length as the original.



If it burns out, you will lose all battery power to the truck. If the engine happens to be running at the time, it will likely stay running off the alternator (provided the fusible link didn't blow due to a short circuit in the main feed wire). But if it's not running, you won't be able to start the engine if that fusible link is blown.

Also, with the addition of the gauge cluster, the main feed wire becomes a shunt for the ammeter (battery gauge). A blown fusible link leaves the shunt open circuit which has the potential to pass a damaging amount of current through the meter movement and it's wiring (the wires you are adding to the #1 & #12 spots). That is one of the reasons it is important to have the 4 amp inline fuses in those wires. They'll blow before enough current flows to damage the meter or wiring.

Thx so much for all your help!

Got everything finished today and everything seems to be working fine so far.

This was one of the hardest most stressful projects I've done so far to my truck. But I have a sense of accomplishment now and my cluster looks great. Will be driving it at night this evening. Hoping all the cluster lights look good.

A few things I'm not sure about since I've never had gauges before.

The oil pressure is closer to the H (high) all the time. I have a crate engine. 330 HP - 350 with vortec heads. Is this normal for the pressure to be on the high side?

Also the battery gauge reads closer to the C rather than in the middle. Battery and alternator are both new. Is that normal ?

Tach acted funny (dropping off or jumping) a few times but then stopped. Now it seems to be acting normal. I installed a tach filter.

When I do anything electrical such as turning on the headlights to tach needle jumps a tiny bit. Normal ?

Again, thanks so much for all your help. I couldn't have done this without you, vettevet and TBONE.

Love this site!!!

[1972BlueC20]

Oh and my junction block post and nut are very corroded. I have a new one ordered and on the way. Hopefully if corrosion is the problem that will take care of it.