Tail Light problem .Any help appreciated

[Grandaddys' 64]

Long time lurker here, but needed help with the tail lights on my 64 Fleetside. All stock with a 230 and three on the tree. Was passed down this truck from my father who got from his father. I have been doing mostly needed things so far. One of those things was new alternator earlier this week. I was wanting to get the alternator in right after it came and made a mistake - I did not pull a battery cable before I started and when I unbolted the hot wire on the back of the altenator it touched the inner fender and sparked. I got the new alternator in with no other issues and checked the truck. No problem cranking and the alternator worked to charge the system. I kept checking, turning on the lights I got headlights, parking lights, dash lights, dome light, tag light, but NO tail lights or brake lights. I am not too good with electrical. Does anyone have an idea?

[Slow Build]

Did you have tail lights before the alt change? It's usually a ground problem on the tail lights. Run a wire from the tail light buckets to the frame.

[Grandaddys' 64]

All light worked before the alternator change. I had already dealt with buckets and making sure I had good grounds when I put LED replacement 1157's in them.

[Grandaddys' 64]

The ground off the battery neg to sheet metal was a worn down with about half the stranding gone so I cleaned that up and regrounded it. No change

[Clyde65]

Checked fuses?
Start running the wires from the brake light switch. I would strongly suggest you get a wiring diagram( they are available on line) so you know what color and where they go. A 12volt test light will be invaluable to you.

Good luck!

[Grandaddys' 64]

Checked fuses - OK. Have factory shop manuals. I am just not good at chasing electrical gremlins. Should I not start before brake light switch?



Maybe where the wires come off voltage regulator or horn relay? (not sure which one)

[TopFuel1966]

If you look at the wiring diagram for your truck you will see that the only things that the two circuits (taillight/brake-directional) share is a common ground and the headlight switch.
The tail/tag lights are fed directly from the headlight switch by a brown wire. The brake/directional circuits are routed thru the brake switch and then thru the turn signal switch connector. The left directional wire is yellow and the right is dark green.
If neither circuit is working then I would start at the headlight switch and work thru to the common ground.

[63C20]

here is everything you need. FYI: the OE switches are made to give you parking lights BUT when you go to headlights use the running lights turn off unless you modify the switch
http://6066gmcguy.com/parklamp6063.html
there is the fix
that site has mucho good info and help
http://6066gmcguy.com/headlight.html