[Gary H]

The turn signal lamp on my 66' GTO isn't working. The bulb is good, turn signals working, and the dash socket gets power and is flashing with a test light. This is a original plastic socket. How does the bulb get ground with a plastic socket?

[johnta1]

Is this bulb one that has no metal base, just 2 wires out bottom wrapped on each side?

[Gary H]

Originally Posted by johnta1

Is this bulb one that has no metal base, just 2 wires out bottom wrapped on each side?

Yes, it's all plastic with one wire in the middle, and one going into it on the bottom, outer edge.

[johnta1]

194 bulb I think?

There should be 1 wire on each side of the base. Flat part.

Not sure how the socket part works on that, does the socket have the wire attached? Then bulb goes in and then put in IP?
Or socket attache at IP and bulb presses into it there?

[Lemans64]

Does the 66 only have 1 Bulb on dash for both side of signals? If so the dash bulb grounds thru the front marker / turn signal. So if it works
on one side and not the other, the opposite side turn signal bulb or housing has something wrong. So if the fronts are not hooked up the dash indicator will not work.
Hope this helps and does not confuse.

[Gary H]

Still can't figure out this issue with the turn signal indicator light in the dash. As I mentioned earlier, the turn signals, both front and rear, left and right work fine. The problem is the dash indicator light doesn't light up. When I check the dash socket with a test light the light blue wire contact in the socket is flashing when the turn signal is activated, and the dark blue contact also flashes when the turn signal lever is turned to the opposite side. The bulb, which tests good, just doesn't light up. And I really don't know how it could since it's a plastic socket and therefore there's no ground. Help! I really hate that this is whipping me.

[johnta1]

Does the socket look like the other one?

I can not remember what they actually look like.
Do they rely on the IP circuit board? If they even have one)
I would say they should have a ground on one side and the power on the other side. (if no circuit board)

I know they had a service bulletin some time about the lamps having the wire on each side not being 'inline' but squished to end of bulb.
(hard to explain, basically the wire should line up with the contact inside holder)

[johnta1]

Happened to find it right off.










This is the bulb type correct?

[Lemans64]

Appears to be similar to that of the 64 with only 1 bulb on dash for turn signal indicators, Correct? OK if so the wire that comes from turn signal switch splits at signal switch, one goes to
dash indicator and other goes to front turn signal bulb. There isn't ground for the signal indicator socket at the socket location. When turn signal is on, power goes to one side of the dash bulb,
power goes thru bulb and out other wire back to turn signal switch and goes out to that side front turn signal bulb and socket where it goes to ground thru the bulb in socket which causes bulb in dash to flash. So possibly you have bad turn signal switch? One could check for ground at bulb socket in dash with key off and putting signal switch to left and right. Did this just happen suddenly or?

Would be nice if somebody had wiring diagram for a 66 to look at, I am only looking at 64 digram and looking at picture of your dash which show same set as 64 in that only has 1 bulb for dash flasher.

[johnta1]

66 wiring dash

[Bill Hanlon]

MAYBE John's diagram is for a '66 other than GTO and MAYBE would not match Gary's 66 GTO.

John's diagram shows separate left and right turn signal indicators in the dash, while Gary's 1st post implies (to me anyway) there is only one turn signal indicator for both directions.

John's diagram shows the right turn indicator on the dash sharing ground via a black wire with most of the other lamps in this order:

Instrument cluster lamp
Right turn indicator lamp
Instrument cluster lamp
Instrument cluster lamp
High beam indicator lamp
Instrument cluster lamp
Instrument cluster lamp
Left turn indicator lamp
Instrument cluster lamp

This last instrument cluster lamp shows 2 ground connections:

1. is a Black wire ending in a large black dot. The dot is similar to the "rheostat splice" shown at the lower left of the picture below, but does not have any other wires connected.

2. is a gray wire that goes back to the headlight switch. I can't read any more info about this wire.

[johnta1]

Bill is correct I believe!



I just used the 1st one I had, which is probably for Pontiac big cars.

Try this from 66 Tempest section (partial pic):

[Lemans64]

This last diagram shows to be same as 64, Single turn signal indicator. so ground goes back thru opposite turn signal side of switch and back out
to front turn signal housing and thru bulb. Should be able to remove bulb and check for ground thru opposite side using wire colour. Does it have LED bulbs in front
signal assemblies?

[Goatracer1]

Have you tried another bulb just for ****s and giggles?

[Bill Hanlon]

For John's second diagram (for '66 Tempest) to work the turn signal switch would have to :

1. when turn signal lever is "off", provide either ground or open to the "Dark Blue" and Light Blue" wires. Electrically it wouldn't make any difference ground or open.
2. when turn signal lever is "left turn" one of the wire sets (lets say Dark Blue) would get blinking 12 volts while the other wire set (Light Blue) would provide ground.
3. when turn signal lever is "left turn" one of the wire sets (lets say Light Blue) would get blinking 12 volts while the other wire set (Dark Blue) would provide ground.

I may be opposite on #2 and #3. Can't tell with more of a wiring diagram than John supplied.

But I guess the original question is still unanswered: How do two wires attach to the turn signal indicator lamp in the dash? And without grounding the metal case of the lamp?

[johnta1]

Full view, not sure how it will look on py.







Looked better than I figured.

[johnta1]

And engine side:

[Bill Hanlon]

The dark blue wire on the turn signal switch (and the dashboard turn signal lamp) will have 12 volts from the flasher when a right turn is being signaled. The light blue wire will be providing a ground via the turn signal switch.

The light blue wire on the turn signal switch (and the dashboard turn signal lamp) will have 12 volts from the flasher when a left turn is being signaled. The dark blue wire will be providing a ground via the turn signal switch.

Thanks for the diagrams John.

[OG68]

This was covered before;

https://forums.maxperformanceinc.com...d.php?t=847504

[Peter Serio]

To reference post #10 above, the black dot (ground) shown in the wiring diagram is not fully a "wire."


It is a steel bracket attached to the rear of the main gauge housing with 2 sheet metal screws. The other end (one bolt) connects to the bracket which supports your brake pedal pivot.

The hole in the brake pedal support was formed in the shape of an oval to allow for some adjustment.


For 1966 A body Pontiacs the dash cluster ground bracket is a one year only part. (All 67 Tempest, Lemans & GTOs used a similar ground bracket (in the same location) except the shape and the overall length of the bracket is different.)