Wiring fog lamps

[mcarnage59]

I recently purchased a set of fog lights and switch for my early 65 from a forum member. I installed them on the weekend and they look great. I purchased an underdash wiring harness and another switch from Scott Drake but the wiring loop to the tail lights doesnt seem to match. They also suggest using power from the back of the ignition switch splicing into an existing wire.

Last night using a test lamp I found another live wire and plug that is part of the exisiting underdash harness. Its not connected to anything just hanging under the dash (There are a few wires under there not connected). Perhaps they used a std harness originally for higher spec cars and just didnt connect what wasnt required.

Is it ok to use that wire for power? I plan on running from it to the circuit breaker and then to the fog lamp switch. I cant see why not and feel its a better option than cutting into power to the inigiton switch.

I sort out the tail light activation later.

[boofhead]

I would expect the docs want a switched 12v source - so anywhere is ok as long as it does not overload the circuit. I would expect the use of a relay as well to reduce load on the switch and it should have a fuse.

[mcarnage59]

I would expect the docs want a switched 12v source - so anywhere is ok as long as it does not overload the circuit. I would expect the use of a relay as well to reduce load on the switch and it should have a fuse.

Fuse in addition to the circuit breaker? Where in the circuit does the relay go?

Electrical not my strong point  Still trying to find my strong point

[GEOFF289]

I don't think the Drake and other similar after market fog lamp kits include a relay but really they should.

Mark, the original wiring harness in these cars has the full electrical load imposed by the headlights going through the headlight switch. While this might have been OK 50 years ago when we only had weak lights it's not really up to the draw of modern halogen or other lights so putting a relay in the system is a common and good idea. There are kits available for this - I got one from forum sponsor Custom Mustangs a few years ago. A relay is just an electrically operated switch really. You mount it close to the lights and the power goes a short distance from the battery (or starter solenoid) to the lights via the relay. A longer and lighter duty wire goes from the relay back to the headlight switch which is then only switching on the relay to complete the circuit between the battery and the lights, rather than having the full headlight draw going all the way from battery to headlight switch and back to the lights. Headlight switches overheat and your lights play up without a relay with a modern headlight fitted.

As Boof suggests, the same issues are at work with fog lights. The Drake kit is really adding to the problem described above by adding the fog lights to the load going through the headlight switch, particularly if you have both headlights and fog lights on together. A relay in the circuit close to the lights themselves would be a good idea, but as I said I don't think these kits usually provide for one so you'd have to modify it. It's not that hard.

You can get a relay from Jaycar or somewhere for only a few bucks. You would need to insert it into the circuit near the lights and run a separate feed from the battery or solenoid to the relay. In this diagram http://www.next.gr/uploads/39/relay_diagram_02.gif the trigger source would be the fog light switch getting power from the source you found, the device would be your fog lights. You would need to cut the wire in the kit that goes from the lights to the firewall, connect the light end to terminal 87 and the other end to terminal 85, then a separate power feed to terminal 30 and earth to terminal 86. Job done!

Boof suggests a switched power source, i.e. only live with the ignition on, but the headlights use a constant power source which I presume is what you found unless you had the key on while poking around with your test lamp.

These links may or may not be useful

http://www.cjponyparts.com/fog-light-wiring-kit-1965/p/WFWK1/

http://www.mustangproject.com/Links/1965-1966%20Mustang%20Fog%20Light%20Kit%20instructions.pdf

Good luck.

[mcarnage59]

I don't think the Drake and other similar after market fog lamp kits include a relay but really they should.

Mark, the original wiring harness in these cars has the full electrical load imposed by the headlights going through the headlight switch. While this might have been OK 50 years ago when we only had weak lights it's not really up to the draw of modern halogen or other lights so putting a relay in the system is a common and good idea. There are kits available for this - I got one from forum sponsor Custom Mustangs a few years ago. A relay is just an electrically operated switch really. You mount it close to the lights and the power goes a short distance from the battery (or starter solenoid) to the lights via the relay. A longer and lighter duty wire goes from the relay back to the headlight switch which is then only switching on the relay to complete the circuit between the battery and the lights, rather than having the full headlight draw going all the way from battery to headlight switch and back to the lights. Headlight switches overheat and your lights play up without a relay with a modern headlight fitted.

As Boof suggests, the same issues are at work with fog lights. The Drake kit is really adding to the problem described above by adding the fog lights to the load going through the headlight switch, particularly if you have both headlights and fog lights on together. A relay in the circuit close to the lights themselves would be a good idea, but as I said I don't think these kits usually provide for one so you'd have to modify it. It's not that hard.

You can get a relay from Jaycar or somewhere for only a few bucks. You would need to insert it into the circuit near the lights and run a separate feed from the battery or solenoid to the relay. In this diagram http://www.next.gr/uploads/39/relay_diagram_02.gif the trigger source would be the fog light switch getting power from the source you found, the device would be your fog lights. You would need to cut the wire in the kit that goes from the lights to the firewall, connect the light end to terminal 87 and the other end to terminal 85, then a separate power feed to terminal 30 and earth to terminal 86. Job done!

Boof suggests a switched power source, i.e. only live with the ignition on, but the headlights use a constant power source which I presume is what you found unless you had the key on while poking around with your test lamp.

These links may or may not be useful

http://www.cjponyparts.com/fog-light-wiring-kit-1965/p/WFWK1/

http://www.mustangproject.com/Links/1965-1966%20Mustang%20Fog%20Light%20Kit%20instructions.pdf

Good luck.

Geoff, thank you for the comprehensive response. Actually I have done any night driving to talk of so havent worried greatly about the headlights. I installed the fog lamos becuase I like the look and thought it would be a bit lame if i didnt wire them up. The second hand switch I got with them looks original and has the ability to fit ring connectors rather than the new one with a seal back and pig tail with a connector. Actually I couldnt work out from the set up how to work it into the tail lamps (not that overly concerned me other than wanting the factory set up) So I am using the old switch. As I said I found a constant power source that is not part of the headlight switch our ingition. From into the Circuit breaker and then onto the switch and out through the fire wall to the under bonnet wiring. (seems ok) Next project I might do as you suggest and fit the relays to the headlights.

[boofhead]

Good post Geoff.

[GEOFF289]

Cheers Boof.