hello friends, i have lost all power to the inside of my car ( 66 chevelle), i found no 12 volts at the harness where it plugs into the firewall to the fusebox, if i apply power there everything works again, so i traced the big red wire from the harness connector at the firewall down to the horn relay, there is of course nothing there, the big red wire is on one terminal with i think one small red wire, another terminal with a black wire and a couple of plug in connectors on the underside, where does the 12 volts come from that goes to the fusebox? is there a fusible link somewhere?, i have nothing at both ends (at the horn relay nor at fusebox) so there isnt a link in that line but without a wiring diagram i am lost, i know some of you guys are real pros from experience.......thanks pals.....

Scroll down in the attached link and you'll see a pic of the typical wiring for these cars and the main junction point.
http://www.chevelles.com/forums/showthread.php?t=100353

If you have no power at all check the black wire on the horn relay, it should go across the rad support to a junction block mounted to the support behind the battery. Check the wire from the junction block to the battery. Sounds like you've lost a connection between the bat and the junction block or the junction block and the horn relay.

that may well be, i have no 12 v on the horn relay, one side is the 12v red wire that goes to the firewall, the other side of the horn relay terminal has a wire that goes to the ground side of my amp guage. if i apply 12v to the horn relay everything inside the car goes back to working properly, but then my amp guage doesnt work......the car has been working for years as it was, i understand that 12 v should be on the horn relay thanks for your help! god bless.......ed

The 12v from the battery goes to the junction block then to the horn relay. The amp gauge is wired across those two points, horn relay/junction block. If you bypass the junction block by running 12v from battery directly to horn relay then your amp guage will not work. Your amp guage is really measuring the difference in voltage between those two points.

well hank, thank you for your help on this. i just got home and checked everything, i have one red lead coming from a terminal on the horn relay and going to the firewall. the other terminal on the horn relay has one black lead going to the ground side of the amp guage, two other red ones on the same terminal, one a little larger than the other. i believe the smaller one goes to the voltage regulator on pin 3 i believe. the other red lead i cannot follow as the wiring is wrapped so tightly with electrical tape. is this red lead where my 12 v comes to the horn relay for distribution? i have followed everything back, there is no junction block anywhere, i have opened the harness and followed from the battery to the horn relay and i cannot find one going from the battery to the relay. where does the other lead go to from the horn relay. that must be a 12v line.......many thanks for your time, you are a blessing to folks like me.....god bless ya!

well i opened my taped up harness, and the other two wires where the amp guage hooks on, one goes to the voltage regulator and the other goes to the alternator. now all of my wires have been traced, but i still have no 12v on the horn relay, should there be 12v coming from my amp guage back to the horn relay?.....this is the only place the 12v can come from....no other wires go to the horn relay except for the horn connections on the bottom of course. i checked with my meter and the terminals on the horn relay arent completely dead, there is 5v there instead of 12v....any more help is greatly appreciated, thank you especially Hank!

Well I'm starting to get a little confused. I'm not that familiar with the 66 but it is essentially the same as a 70. Start at the battery. Should have two wires coming off the positive post. The large one should directly to the starter and does not feed anything else. The other one is the one you're interested in. This is the one that supplies power to the main harness until the engine is started and the alt takes over. You need to trace that wire to the horn relay. The wire may look good but be corroded and broken inside the insulation. Here is a pic of how the wiring should be run. Notice the fusible links in the schematic, meter voltage both sides to make sure they're good.
http://madelectrical.com/images/chevym1.jpg

i found the poitive lead from the battery, it is going to one side of the amp guage, but it is the right one, it is spliced right over the horn relay, obviously the old guage was a type where 12v went thru it back to the horn relay. my old guage that was in the car since forever pegged out on me so i just bought a whole new 3 guage set, i noticed everything was dead when i pulled the guage loose to test it and i had to bolt the two leads together to get power back...what i decided to do is put the original source lead back onto the horn relay where it was originally and remove the wiring to the guage and rewire it to ground and to the fuse box like the instructions say to do....it was the guage that i was using before , i dont know how i was getting 12v thru it but that is how it was getting juice back to the relay.........so i got it about all figured out......hank, thank you sooo much, i HOPE i can return the favor, i sure could not have figured this problem out with out you! god bless and i hope your blessings are doubled! thanks again! ed