Wiring rats nest

[motolover]

The previous owner really hacked up the wiring in my 66 gmc. I am a novice when it comes to wiring but I was wondering if anyone could point me in the right direction as to where the 2 purple wires that are twisted together go? Also it looks as if I am missing the tab in the bottom right of my fuse panel for a fuse to snap into?.

[Funky61]

Here is a 1965 schematic from the Jolly Disc that might help.

Neutral Safety Switch, top right, shows two VIOLET wires but only for automatic transmission

* I see that light Green wire is an add-on and not a color on the schematic color key

That is my guess and I hope someone else will chime in...

Good luck and let us know how you did.

[James]

That missing tab goes to your dome/tail light. Do they work?

[motolover]

The dome light is not hooked up and I have the box off so I have not been able to hook up the taillights. It has an automatic transmission, I am also fiddling around with the turn signal switch as my original one was bad so I had to get one from a 63 chevy that would work. I am trying to figure out that color wire on the 63 turn signal does what.

[lizziemeister'sV6]

Bad news - GMC and Chevrolet turn signal switch are not alike - they are numerous differences between the GMC and Chevrolet trucks built prior to the early 1970's. Don't reply on much help from parts vendors and assembly manuals that lump GMC and Chevrolet together - My advice is to save everything you can from your wiring such as ends/terminals and scout around and find parts/pieces of ORIGINAL to your truck and go from there. The aftermarket part sources are junk - think China.

[AZKen]

1. The missing fuse and holder terminal is for a spot light. That's why it says "SPOT LP". It's common for that to be "missing" if not RPOrdered. Your tail light/stop-dome fuse is in place.
2. If you want to know how to hook up the turn signal wires, advise the colors coming out of the switch.
3. The neutral safety switch wires (violet) look like someone was bypassing the switch. One vio wire from the switch goes to the solenoid via the 6 pin firewall connector on driver side. The other vio wire goes to the ignition switch solenoid terminal. Switch is probably bad. That's why the bypass.

Does the truck start?

You only have one other issue, that was almost 2 years ago. (454 swap)

[motolover]

The problem i am having with the turn signal is trying to figure out that color wire goes where. The new switch i got has different color wires than the factory ones. And I can say putting the 454 in has definitely made things alot more difficult

[AZKen]

Please read the posts carefully. Read no. 2. Tell me what the colors are!!!!!!!!!!!!!!!!!!!!!!!!!!! Coming out of the 1963 switch that you have.
Can you please give me the part number and vendor of the turn signal switch you bought.

Please answer the underlined part above. DOES THE TRUCK START ? We can't help if you don't give us info. We don't know anything about the situation until you tell us.

We CAN get you wired if you answer the questions.

ALSO: Do you need help with the 454 install?

[motolover]

The switch was ordered from classic parts part # 53-507.
The wire colors are yellow, light blue, white, dark blue, pink, and purple.
Yes the truck starts and runs right now, the 454 purrs like a kitten.

[AZKen]

1. YEL- to flasher L
2. DBLU- RH front park/turn
3. WHT- Brake switch input
4. LBLU- LH front park/turn
5. Pink- LH rear turn/stop
6. VIO- RH rear turn/stop

The above matches 1963 Chevy wiring diagram and 1963 GMC diagram. There may be small changes made to 1966 wiring. But now you know what the switch operates so you can trace your truck wires to see where they go and hook them to the switch wires per my info. The colors may not match your truck wiring.
Looking at the wiring diagram that funky posted and assuming it is the same for 66 GMC and assuming your wire colors in the truck are original, I figure it would wire like this below:

To wire the 1963 Classic Parts switch 53-507 to your truck: (not 53-507A)

1. T/S switch YEL to truck VIO
2. T/S switch DBLU, LBLU and WHT......same as truck
3. T/S pink to truck YEL
4. T/S VIO to truck DGRN

You will have a black wire in the column for horn. It is DGRN on earlier trucks. Does not need to go thru T/S switch.
You may also have a gray wire for automatic transmission column indicator light. Does not need to go thru T/S switch.

Please be sure to check my info before energizing anything. To double check, check by function not color. I.E. tracing truck wires.

Other members may see it differently. So give it some time.

As I said, the NSS has been bypassed by twisting the two VIO together, that's why is starts.
The light green and dark green wires on the NSS are for the back up lamps.