Wiring question - installing optional gauges 66 full size
 

I am installing a speedometer head with the oil and temp gauges in my 66. The previous cluster has two green wires to the temp gauge. One goes to the temp sender, the other appears to go to the ignition switch. Someone suggested that is so that in crank position, the temp light comes on as a test to show you it's working.

My question is, can I safely leave this hooked up with the new temperature gauge or do I need to remove the green wire from the back of the ignition switch? I have not tested but it only makes sense that the green wire to the ignition switch makes a ground in crank position to power the light, yet that seems backwards? My reasoning is, the other green wire (which is in tandem with this one) goes to the temp sender and I know the temp sender makes a ground to turn on the light.

That's what I had to do on my 67 GTO.
Otherwise, don't expect the gauge to last very long with it slamming over the pointer every time you crank the engine.

I'll willingly stand corrected but I think this dash loom is for a '66 unit with accessory gauges.

http://www.ebay.com/itm/Original-Das...7b1133&vxp=mtr

It has the two globes at each end. Somewhere in the back of my mind I've read about this before...

Maybe I'm right? Quite possibly I'm wrong????

Ian:ausflag::ausflag::ausflag:

You have to modify the harness. You can not just swap out the wires for the idiot light wires to the gauges. I have had the harnesses out of the cars side-by-side and they are different. I was able to modify the idiot light harness to be the same as the gauge harness, but the lighting is different and the connections to the gauges are different IIRC. The hardest part was getting the correct lamp holders added in.

Also, I think the gauge cluster is a '65 style cluster with all the metal bulb holders without the plastic loom on the back like the standard '66.

It has been years since I did this, but there was more to it than I had hoped when I started the project.

I have done this swap twice over the years and have found that the most important reqirement in making sure everything fits (and it will fit) is lots and lots of patience. The project is not that hard but if you are in a hurry you will snap or bend or break or scrape something.
The wiring issues cannot be that difficult since the first time I did the swap I did not have a clue what I was doing and the unit is still working 20 years later.

Buy the accessory wire harness for the gauges, and make the appropriate modifications to the main harness. Not a difficult conversion. By default the under dash wire harness was setup to fit cars with idiot lights, not gauges. So PMD made the gauge option a modular procedure during assembly. Instead of having multiple variations of wire harnesses, they just added small wire harnesses for whatever accessory was added to the car. i.e. tach, oil/temp gauges, and even the parking brake indicator. I made the same conversion last year. If you want more detailed info, I'll dig it out of my box o' parts and let you know what you need to do, and what you can leave alone.

Post it man!

:popcorn:

MPKIND - do you have a '65? If so, you have the metal bulb holders for all the lamps in your cluster. '66 idiot light cluster has a plastic loom with bulbs that push in and do not have the bayonet base. It would be much easier to convert the '65 since it has the same bulb arrangement.

I should have explained, this is on a Canadian 66 full size. They use a printed circuit on the back and don't look anything like the US version. I snipped the plug off my stock harness and made up my own harness. I have it all functional and tested using a signal generator (Special tool that GM dealers have). However, the extra green wire has me wondering and I don't want to put it in to the car until I get it sorted out.

Because the green wire is not the power wire for the gauge, that is what has me asking. The pink wire powers the gauge, the green splits, one side goes to the temp sender, the other side to the ignition switch.

Yes, posting up your experience would be great.

I'm betting you will let the smoke out of the temp gauge if you do!
Check your schematics closely. It's purpose was to test the temp light every time one cranks the engine.

Signal generators are common in electronic testing circles.

Charles

I agree. I think it's going to be removed from the back of the ignition switch. I've never heard of a terminal on an ignition switch thats sole purpose is to create a ground in crank postion, which is what this would have to do to test the gauge. The gauge is powered by the pink, grounded by the green that goes to the sending unit. That green splits with the other 1/2 going to the ignition switch.

Does anyone have the wiring diagram for a 66? Or is it online anywhere? I'd like to take a look at it.

65 full size at bottom of this page. Probably darn close.

http://www.oldcarmanualproject.com/t...ing/index.html

I'm sure I have one, I'll try to post later today.

I looked at that one and it doesn't seem to mention any difference, light or gauge. And yes, the green splits, one to the sender and one to the ignition switch.

Thanks, if you do that would be great. I'd like to be able to print a copy to have.

More interest than I expected on this. I'll get that harness out today and take some pics to go with it. I suspect the overall schematic is very similar between 65 and 66, so that probably isn't a major concern. You just want to know how it all comes together with the accessory harness added on for gauges. I should have a repost with pics by tomorrow.

Here is a '66 I have in progress. Only thing keeping it from being done is a few of the little copper crimp on contacts that go inside the metal lamp holder. I added a bunch of the accessory bulb holders to avoid making one of the giant factory crimp connections they wrap with tape.

The top one is the entire gauge cluster with harness.

The black is a harness from an idiot light '66. This loom will not fit on a gauge cluster. I don't know diddly about a Canadian car, but thought I would post this for future Ref in this thread.