Hello, I am trying to hook up my 400 hood tach on my 1969 Firebird 400. When I bought the car the tach was already on the hood but was not wired. After some research I found that the tach needs to have ground, 12volt power, and a 12 volt connection to the distributor. I am having trouble identifying which cable is which, ground, power and distributor, can you advise?

The three thicker cables you see are two black, and one brown, any idea? thanks in advance!

I don't have that circular circuit board in mine! On mine the blacks are ground (combined with the 2 lamp black grounds) and the red wire would go to your coil. Not sure what you have there!

What the?!?!

Does not look right at all.

im also wandering, if I test around the cables by hooking one to the distributor and another for ground, do you think there is a big possibility of damaging something by having a wrong connection?

that may be why its not hooked up...just for 'looks'...??

I don't think if you try it momentarily to ground and the coil wire in various ways it will hurt. If its MSD or Pertronics they are pretty robust. Points no problem for sure, but not knowing what the circuit board is....

Could be a nuclear detonator??

I have a question about hood tach wiring as well. I bought a new OER 68 hood tach from Classic and have it mounted. It came with absolutely no diagrams or instructions. There is a black wire, a black with pink stripe wire, and a grey wire. I am thinking Black is ground, Grey is tach lead to coil, and black/pink is light hot lead. Is that correct?
kelly

Yes meshat, you are correct. A good "power" source is right below the hood tach, the wiper motor. If you piggyback the power lead for the tach right off the wiper motor power lead, it will lights up as soon as you turn the key, just as it should. It is very simple, crimp a striaght blade connector to the power wire for the tach and push it the plastic connector plug that plugs into the wiper motor. It's a perfect power source, quick and simple!

I know what Isaac's problem is..... What you see is the circuit board out a newer round tach mounted to the bottom of the old tach which probably stopped working. The wires were connected to the old tach gauge. I think if you do like Dave sayed you'll find out what wire goes where...

So the black with pink stripe is the light hot lead then and the grey is the tach lead to the coil? Why would one want to have the lights in the tach on all the time? wouldn't a switched hot lead to the dash light circuit be better or is it to help with lense fogging? and I think I read somewhere on the FGF site that I am supposed hook up a small length of tubing from that nipple coming off the bottom of the tach over to the heater box? to stop fogging? Do I need to do that or do most just cap that? or leave it open to breathe in warm engine air? or what? thanks for your help folks.

I been so busy lately haven't got time to try anything as far as hooking up the wires, but thanks to everyone for your help.

I just hooked up my OER tach the way you guys mentioned but it did not work. My car would not start. I peeled the factory tape off of the OER tach harness and noticed that all the grey wires are hooked together and go to the tach lights. The black with pink stripe wire goes only to the tach. Soooo I hooked up the black with pink stripe to HEI tach terminal, black to ground and grey to power/ignition on. This works perfect. The grey wire must be hooked to ignition power or the tach won't work. If you want the lights in the tach to work only with lights on, you would have to seperate the grey wires in the tach harness. The grey wire that goes into the tach gauge, ( must have tach apart to see this) must still go to ignition power and the grey wires that go to the tach bulbs would than go to lights on power. Most after market tachs have four wires which make it easy to have the tach light hooked to a lights on power wire. Just my two cents...well, if you add up all the bills, tach, hood, scoops hood emblems, paint ect its more like " my $1000 ". Hope this helps.

This is exactly the thread I needed! I have one question though... here is where I sit, I have three wires to work with:

I have the one wire connected to the HEI distributor "tach" point.

I have a good ground (tested it with my multimeter)

I have the wire that is my equivalent to your "gray" wire hooked up to the window wiper motor power.

My tach lights come on, but the tach does not work.

Where is or what is the power/ignition wire rsclassics used?

I am good at tracing down wires... and apt at reading an electrical diagram, but I am a bit short on some of the knowledge as far as what is what...


Thanks!

(for those that have seen my other posts, I did get my brakes squared away, and the exhaust is going to cost me ... needs a lot of work... I figured this would be a cheep easy fix I could do myself... also clean up some wires!)

Ok, I am going to guess and go with the power going to the HEI distributor. I will let everyone know if it works or not!

One thing I have learned is that with some MSD and or Pertronix conversions, if the tach does not read right away when you start the car, give the tach a good tap on the top. I've seen this work time and time again when people think there is something wrong and they think there is something wrong with the tach.

I think it has something to do with the old points system giving off an initial "jolt" of voltage that more or less jump started the old tachs whereas with the newer HEI conversions etc. you do not get that initial "jolt" as the newer systems are more regulated right from start up.

I hope that all makes sense and again, this is just my theory but it has proven true on a few occassions now. If this does happen, these tachs will start working once you start the car and drive for a few minutes or give the tach a "tap" and I bet it works. I know this is not how you want to get your tach working every time you drive your car, but I'm not sure how to correct that either...

That's wierd Joe. I have the petronix setup in my car and never have that problem. I did have a problem when I first hooked my tach up but don't remember what it was. I have been tempted to seperate the hot wire for the lights to make them a switched source. But for now they go to power supply on the wiper motor.

Thanks, yeah I have not gotten around to checking it out yet. I am going to try a few things and I will let you all know what I find out.

I do know the hood and hood tac are aftermarket, so it may be a cheepie POS... will dig into the tach once I try a few things.

Success!!!

Lesson #1... Do not EVER trust electical work done by previous owners.

Problem: The ground was hooked up to the window motor wire, the "hot" wire was grounded. This allowed the lights to work, but the tach did not get power.

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For future reader's referance:

My system's hood tach, working with an HEI distributor, is wired with a three wire system.

Hot wire: To the window motor's power.

Ground wire: Grounded to the firewall.

Distributor wire: Attached to the "tach" plug on the distributor.
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Now on to the window motors... :P

I have a 1967 400 numbers match with auto trans. does anyone know if an auto car came with a hood tach? I like the look, but may not make sense as on a 4 speed car?

It was an option. It could also be dealer installed. Lots of people add them (myself included) even if it wasn't original to the car. If you like the look, keep it.

Thanks for the information.

Confirming that rsclassics' guidance to wiring an OER hood tach worked for me. Connected the gray wire to positive (ignition), black to ground and black w/ purple stripe to the tach wire at the distributor. I'm using an MSD Ready-to-Run. I must tell you, I was dead in the water before reading rsclassics post. Turns out I had the positive (ignition) and ground wires reversed. The light worked, but the tach would not.

Absolutely correct one people don’t realize is that you have a factory tachometer and you have your hood off the car will start momentarily then shut off because that wiring harnesses the power feed to the coil positive side.
Just my one cent

A follow up point is at 1969 Firebird Pontiac has a special ignition switch the careful with aftermarket one where when the car cranks there’s 12v to the distributor then it drops down to 9v so it doesn’t burn out the points. So the point is it has 2 power sources. Anybody needs any photos of placement and cars I found an original 1969 400 car original engine possible and 323 gear even has original battery in it it runs pretty good just had dust all over it. It’s nice to see all the original hoses decoded and harnesses in the correct spot so you can see when you’re restoring something.

The feed to the coil on GM cars is thru a resistor wire or an actual resistor and the second feed wire comes up from the R terminal off the starter which gives it the 12v on crank. There isn't a special pontiac firebird ignition switch.