This might be what you need https://www.gtoforum.com/posts/939057/

 

This might be what you need https://www.gtoforum.com/posts/939057/

Thanks, I feel more like an idiot though. I didn't see that "Armyadarkness" post in my forum search yesterday so my bad there. I also bought the Assembly Manual last December but never thought to look at it because this was a dealer installed option, so thanks for pointing to that too. I'll admit, I find page 453 intimidating and I'm an engineer!, so I'm not starting out this project on the right foot. Looking at the pg. 453 diagram refers to "breakerless ignition only" in a few locations ( transistor? ) and if that's the case, why is there a connection to the coil? I don't even know if I have the right tach now. It's looking like finding a place to put the hole is now the least of my worries. The hole apparently is 3 3/4 diameter and lines up with the body plate and is partially over the hood supports in from the cowl but the distance in from the edge of the hood seems to be 6,000 miles give or take, so that's a bit confusing. In the end, I may just eye ball it and see if it's conveniently visable from the drivers seat and looks right from the outside. Since it was a dealer installed option, I'm pretty sure the placement would have varied somewhat. Does that make sense? At 78, I may just be getting too old to figure this out on my own that's for sure. It would be interesting to see what a Pebble Beach or Monterey car show judge would look for doesn't it?

Thanks again, this was very helpful

 

You're doing your homework before cutting, and that is a great plan! Others here have done it and I am sure will chime in. Regarding the breakerless ignition reference: sales code 671 / UPC code K66 - Capacitor Discharge Ignition System was an option for 1967. It cost $114.80 with AC and $104.26 without. Good info on it and how to ID it here: https://forums.maxperformanceinc.com/forums/showthread.php?t=425994 If you have the PHS docs for your car it would tell you if your car came with that option. My understanding is it was not commonly ordered. Of course 58 years later you could have any kind of ignition system in there, so you will need to physically verify what is there. An NOS tach from back in the day is a great piece to have and there are good sources for upgrading it if needed to work with different ignitions. I would start by identifying what you have for an ignition system and then go from there.

 

This might be what you need https://www.gtoforum.com/posts/939057/

This is a picture of the tach underside

You're doing your homework before cutting, and that is a great plan! Others here have done it and I am sure will chime in. Regarding the breakerless ignition reference: sales code 671 / UPC code K66 - Capacitor Discharge Ignition System was an option for 1967. It cost $114.80 with AC and $104.26 without. Good info on it and how to ID it here: https://forums.maxperformanceinc.com/forums/showthread.php?t=425994 If you have the PHS docs for your car it would tell you if your car came with that option. My understanding is it was not commonly ordered. Of course 58 years later you could have any kind of ignition system in there, so you will need to physically verify what is there. An NOS tach from back in the day is a great piece to have and there are good sources for upgrading it if needed to work with different ignitions. I would start by identifying what you have for an ignition system and then go from there.

This is the window sticker I had done by Mike Noun. Looks like that option was expensive back then. I bought the car second hand in 1969 for $1,600. ( long story in here somewhere). The PHS documents I have don't mention it either. I'm pretty sure my car doesn't have the Capacitor Discharge Ignition. The distributor looks the same as my other cars I had prior to 1967 with points and condenser inside. I think I just need to see what my Tach is for. I'm pretty sure it's for the points system but I'd hate to blow something up. I've done enough of that in the past. Can you tell by the wires in the picture?, 2 are obviously for the light and one of the other wires is black with a red stripe that I assume goes the negative side of the coil and the gray wire is the 12v feed. Once again thanks for bearing with me on this, I really appreciate it.

Great information,

 

The early factory/dealer hood tachs did not use a 12 volt ignition source.

The grey wire is for the lights and is connected to the dash lights under the dash. The clock lighting harness should have a spare terminal.
Black/Pink goes to the neg coil
Black is ground
Drawing is from the 68 Service manual.

As an FYI for anyone buying a factory hood or dash tach, the 5500 Redline tachs were primarily for the OHC six. Pontiac used the face plate from the OHC tach for the RA II tachs. So be careful what you buy.

 

That's really interesting. The one I have is looking more like an aftermarket thing in a GM box, but there are no instructions in the box. Previously, I'd purchased a tac for the dash to replace the clock on ebay which is always precarious I know but the rear of that is pictured below. I was reading later that with just 2 terminals it's more likely for the other Capacitor Discharge system so I was hesitant to put that in with all the work needed under the dash. So... now I remain confused and scared. Would this thing work with a points ignition? At least I can test it off the car though. The quality is also suspect and is probably made in China. Using the existing light socket, it looks a lot easier with just two terminals and the face "looks" correct but now I don't trust it either. I'm slowly learning that the aftermarket parts for this car are full of sketchy stuff you can waste your money on.

 

do you have a photo of the top of the hood tach showing side and face views?

 

 

BTW, How do you just put a thumbnail instead of the huge version in here. I seem to put the big one AND the thumbnail in.

 

According to people with more knowledge that I, the CD tach would have different internals. See post 8.

http://forums.maxperformanceinc.com/forums/showthread.php?t=521098&highlight=transistor+tach

I would think that CD tach would be very rare and odds are yours is a standard one. Most aftermarket tachs will work with either type system. That could be why your repop dash tach looks like a CD unit.
Here are some excerpts from the 1967 Pontiac Service Manual that explain the CD system and show the related distributor part numbers. Others here may have an idea of your tach from the pictures. I am not familiar with the early ones.
When you upload an attachment, click insert thumbnail. You can also preview your post to see if looks how you like it.

 

https://forums.maxperformanceinc.com/forums/showthread.php?t=767876&highlight=1967+hood+tach

This is from the GTO Restoration guide.

 

According to people with more knowledge that I, the CD tach would have different internals. See post 8.

http://forums.maxperformanceinc.com/forums/showthread.php?t=521098&highlight=transistor+tach

I would think that CD tach would be very rare and odds are yours is a standard one. Most aftermarket tachs will work with either type system. That could be why your repop dash tach looks like a CD unit.
Here are some excerpts from the 1967 Pontiac Service Manual that explain the CD system and show the related distributor part numbers. Others here may have an idea of your tach from the pictures. I am not familiar with the early ones.
When you upload an attachment, click insert thumbnail. You can also preview your post to see if looks how you like it.
View attachment 190350 View attachment 190351 View attachment 190352 View attachment 190353

I think you are correct. It certainly sounds correct at this stage. Thanks to all for the input today. I've learned and accomplished more here today than all last week stewing over these issues and reading random sales literature and comments. It's been a refreshing education also.

https://forums.maxperformanceinc.com/forums/showthread.php?t=767876&highlight=1967+hood+tach

This is from the GTO Restoration guide.

View attachment 190354 View attachment 190355 View attachment 190356 View attachment 190357

Thanks, I absorbed everyone's input and plan to start the project next Monday. I will make a paper template for the placement of the hole ( if anyone would like one in the future) and a picture of the car with the tach on. I'll call it the consensus hood tac. There will be a 3.5 inch dia. hole, 10.0" from the left fender at the hood intersection and 8.125" from the start of the hood at cowl vent. Since the new tac will work with my points ignition and the wire harness consolidates to three wires, the black and pink stripe wire goes to the negative terminal of the coil, the gray to the dash light gray wiring at the "acc" fuse and solid black to ground at the attaching bolt of the regulator on the firewall. Finally, I'll have the wires enclosed in the black split plastic tubing so it looks like the setup belongs there. Any comments to the plan will be very appreciated before next Monday when I pull the pin on this grenade. Thanks again to all. BTW, the hole will be drilled through part of the hood support under the hood surface sheet metal but I can imagine some people have moved it forward to avoid that. I would like opinions on using the "acc" fuse as well for the right power source connection (for the gray wire.

Thanks again

 

I think you are correct. It certainly sounds correct at this stage. Thanks to all for the input today. I've learned and accomplished more here today than all last week stewing over these issues and reading random sales literature and comments. It's been a refreshing education also.

Thanks, I absorbed everyone's input and plan to start the project next Monday. I will make a paper template for the placement of the hole ( if anyone would like one in the future) and a picture of the car with the tach on. I'll call it the consensus hood tac. There will be a 3.5 inch dia. hole, 10.0" from the left fender at the hood intersection and 8.125" from the start of the hood at cowl vent. Since the new tac will work with my points ignition and the wire harness consolidates to three wires, the black and pink stripe wire goes to the negative terminal of the coil, the gray to the dash light gray wiring at the "acc" fuse and solid black to ground at the attaching bolt of the regulator on the firewall. Finally, I'll have the wires enclosed in the black split plastic tubing so it looks like the setup belongs there. Any comments to the plan will be very appreciated before next Monday when I pull the pin on this grenade. Thanks again to all. BTW, the hole will be drilled through part of the hood support under the hood surface sheet metal but I can imagine some people have moved it forward to avoid that. I would like opinions on using the "acc" fuse as well for the right power source connection (for the gray wire.

Thanks again

Just for fun I wanted to see what Artificial Intelligence, "AI" had to say about this, so I typed into ChatGPT "what is the factory location of a 1967 Pontiac GTO hood tach". It's comical, it says it should be 9" from the center of the hood and you should drill a 4 to 5" hole to accommodate it. Also, it's 5.25" from the " the back edge of the hood" Makes you wonder what our future generations are going to end up with on a number of topics. ChatGPT - Pontiac RPO Code Information

 

I just completed the thing after weeks of distractions. Car is a little dirty but the bottom line is, all went well. I talked to a guy that I met at a big car show here in Houston that worked for Gay Pontiac for some 30 years and he recalled the dimensions but they were just from memory. I filed his with all the rest I found at various places and ended up with it being 8 3/8" from the end of the hood at the cowl and 8 1/2" from the LH side of the hood. In the end, I feel confident that nobody has definitive answers since the Assembly Manual has errors. It looks right to my own recollection, and it will have to do. I'd still like to talk to a concours judge about it however. Sorry about the giant picture. I meant for it to just be a thumbnail.