Also. Maybe it needs a good strong battery to run the horn. I will fully charge my battery. 

Ok.  Took my tester and touched green light at c6. Got power.  Then thought I needed the relay out.   I got it out !!! When I shake it it sounds like a pile of dust in there.  Here are some photos.   Good or no good??? And I now need to clean female spade connectors.  Do I use contact cleaner???

Just now, Shawninvancouver said:

Ok.  Took my tester and touched green light at c6. Got power.  Then thought I needed the relay out.   I got it out !!! When I shake it it sounds like a pile of dust in there.  Here are some photos.   Good or no good??? And I now need to clean female spade connectors.  Do I use contact cleaner???

 

Use a screwdriver and pliers and bend these two tabs back.  The board with the parts on it will come out.

It will probably look like this inside.

Cool.  Did you fix that one up to work again??🤓

No, it was No Good.  I had a spare.

Your relay is a typical 4 pin relay (two of the pins in yours are connected, that's why you only have three terminals).  You can buy them for a few dollars at any auto parts store.

19 hours ago, Shawninvancouver said:

Ohhhh. And does anyone see any fuse in common with horn heater fan power antenna abd gauge lights ???

The horn and wipers use the 10 amp fuse in position 10. You can look up the others in that table I posted. I've attached an Excel copy in case anyone wants it. This table is specific to the 260Z and has not been reviewed for accuracy.

Wiring Cross Reference.xlsx

Here's a concise explanation of how a relay works if you need it. 

https://www.12voltplanet.co.uk/relay-guide.html

I have a box of generic 12v relays to replace mine as they become faulty or for rewiring circuits (e.g. lights) that over tax the frail wiring of my Z. 

I saw you had a continuity light, do you also have an ohm meter? You may need it to check the fan on your heater.

3 pages about a horn not working..  Does the Horn make Horny sounds yet?  😉   Get a good battery, it uses a lot of juice!

It sounds like its likely a relay problem as Zed H pointed out. Did you get the relay open yet?

Zed H: Any idea how a relay can get so corroded? How bad were the rest of the relays in that relay panel? 

If the windshield seals leak that's where the water path is to the floor, depending on at what angle the car is parked.

On 6/28/2021 at 8:44 AM, dutchzcarguy said:

3 pages about a horn not working..  Does the Horn make Horny sounds yet?  😉   Get a good battery, it uses a lot of juice!

Kinda reminds me of: Give a man a fish vs Teach a man to fish.

The FSM wiring pages, aside from persisting errors, are really good - but only if you understand the symbology and how the components SHOULD function.