OK, now this one just has me floored. As I've posted before, the headlight revolve circuitry in my '66 still-new-top-me Franken-Charger is just a mess. Wiring all chopped to hell, connector plugs cut up, etc. One or more of the previous owners did a real job on that circuit, apparently trying to hotwire the headlights to revolve. The revolve motors work fine if you do hotwire them so it's just a matter of sorting through all the mis-wiring and getting all the feeds right again. OK, so I'm finally getting around to doing that. I had put off doing so because I couldn't find the connector pigtail for the headlight closing relay. I fished around a few times but it's difficult to see that part of the wiring harness inside the dash, even with the glove box liner pulled out. Finally, I groped methodically backwards down the harness branch from the opening and control relays until I could feel the connector plug for the closing relay.

It is connected to another headlight revolve relay.

Uh, say what, Batman?! Why is there a third revolve relay in my '66? Like I said, it's difficult to get a proper look but there clearly appears to be a third revolve relay installed in the car, except this one is mounted below the tachometer sending unit, not on the firewall. I can't read the serial number but it sure looks a third revolve relay, with the plug for the closing circuit connected to it. No, I am not confusing the control relay for something else: with the glove box liner removed I can clearly see the opening relay, control relay and closing relay--left to right--just as shown in the '66 service manual. So where did the third revolve relay come from?

Now, you might assume that some previous owner replaced the closing relay by mounting a replacement nearby, but why not just swap out the original closing relay? This third relay, wherever it came from, is awkwardly mounted on the support for the tach. sending unit--much easier to just pull the original closing relay and replace it. Plus all three revolve relays are dusty, old OEM units that look like they've been living behind the dash for fifty years. Wherever this third relay came from, it looks like it was installed at the factory.

I don't get it. I have owned or worked on probably a dozen old 60's American cars, some of them pretty hacked up, and I've never run across a mystery part like this. Lots of post-build fixes or mods but not a part that sure looks like it was installed on the assembly line but isn't in any of the service manuals (as far as I can find).

 

YES. 1966 and 1967 had 3 Relays.... If you cant find the correct relays you can perform an upgrade in the system.
http://www.retrorarities.com/images/...lampRelays.pdf

 

Just to confirm, after another round of working on the headlight circuits, my sled has four relay modules installed behind the glovebox--three on the firewall and one below the tach sender. What gets me is that all four relay modules look to be OEM stock and factory-installed. It's not a big deal, and I'll likely replace them all with aftermarket relays as Racerhog suggested, but I am puzzled and curious. The way that second closing relay is installed on the dash brace strut, it has to be an OEM placement. I don't think you could even install that relay, after the car was built, without pulling apart the whole dash, and I see no signs that has ever been done.

It's not a big deal, but this is odd and I'm danged curious. I know it's not that uncommon, especially in that era, for cars to come off the assembly line with glitches that required post-assembly repair. But if that were the case, why would they have installed a second headlight closing relay instead of replacing the first one?