Topic: 65 GT Fog Light switch installatiion

[Brian Conway]

     Thanks for explaining how to check this out.  Yes, I did mean that great gob of tape nice to know it is stock and I won't be unraveling it.  Question; with the key in the ACC or On positions and I switch the fog lights ON.  No response/lights.  With the key in the ACC or ON positions and the headlights on the fog lights do come on when toggled.   Doesn't that indicate the switch's fog light circuit is OK ?  Right now the switch only has power when the headlights or running lights are on.  Brian

[midlife]

     Thanks for explaining how to check this out.  Yes, I did mean that great gob of tape nice to know it is stock and I won't be unraveling it.  Question; with the key in the ACC or On positions and I switch the fog lights ON.  No response/lights.  With the key in the ACC or ON positions and the headlights on the fog lights do come on when toggled.   Doesn't that indicate the switch's fog light circuit is OK ?  Right now the switch only has power when the headlights or running lights are on.  Brian

Normal power to the foglamps is through a circuit breaker that has as its input power a battery-sourced line.  The CB acts as a "fuse".  What your condition indicates is that either you do not have the CB wired up to the foglamp system or the CB is blown: your foglamps simply are not getting power.  When you turn the headlights on, the foglamps feed into the rear running lights---hence the headlights are now feeding power to the foglamps through the switch itself. 

Be careful with the wiring around the CB.  One line is from the foglamp subharness (it accepts power from the CB); the other line is always hot and is not fused.  Both wires terminate in ring connectors.  The wire colors are light blue/black stripe.  When working on the foglamp CB, it is always best to disconnect the battery to ensure there are no shorts.

[Brian Conway]

Concerning the FOG LIGHT CIRCUT.  I have done a little research and have determined;
1.  At the dash harness side there is NO CONSTANT POWER.
2.  With the parking lights engaged the outboard male post, solid black w/C5ZB far right, is HOT
3.  With the circuit tester connected to the Hot post and probing the center male post, grey wire , probe lights up.
4.  With the circuit tester connected to the hot post and  probing the male, Lt. blue w/black stripe, no response
     
This is the OE harness and I have not fiddled with any of it until now.  So between the battery and the harness plug is a cb/fuse ?  Or should I be looking for something else.  As mentioned there does not seem to be a schematic for any of this and I do appreciate the help.  Brian

[jwc66k]

Brian,
  The circuit breaker is mounted to the brake support bracket on the right hand side (66 is mounted to the rear of the windshield wiper motor bracket). There should be two blue/black stripe leads attached with screws to two studs on the circuit breaker. Both leads go to the main harness. With the battery installed, the ignition off and the fog lamp switch off, using the test lamp, you should get power to both studs. If you only get power to one stud, the CD is defective.
And, as you surmised, there is no 65 wiring diagram, at least that I haven't found one yet, so I use the 66 version, which is close. The best info is from the 65 Mustang Electrical Assembly Manual.
Jim

[Brian Conway]

     The dash harness wireing appears to be from left to right; Grey w/Black stripe, Solid Grey and Solid Black.  The switch harness is Left to right; Black w/Blue stripe, Grey and Solid Black.  The fuse block has two fused wires attached; at least one wire appears to be Solid grey w/ Black stripe.  Putting a test on the 10 amp block one post tests good the other not.  Brian

[midlife]

     The dash harness wireing appears to be from left to right; Grey w/Black stripe, Solid Grey and Solid Black.  The switch harness is Left to right; Black w/Blue stripe, Grey and Solid Black.  The fuse block has two fused wires attached; at least one wire appears to be Solid grey w/ Black stripe.  Putting a test on the 10 amp block one post tests good the other not.  Brian

That nails it.  One side of the Circuit Breaker (which you call the fuse block) will always be hot (the battery input side).  The output should also be hot if the CB is working.  As you state the other post is dead, then the CB is dead.

[Brian Conway]

Well thanks for all the help certainly made the process a lot easier.  Reasons for the failed 10 amp circuit breaker ?  The only thing it services is the fog light circuit.  Should I be looking for something else ?   The 65 Wiring Manual does not have the Fog Light Circuit diagram the 66 Manual does.  Brian

[jwc66k]

Reasons for the failed 10 amp circuit breaker ? 

1 - Old age.
2 - Someone shorted the hot fog light lead to ground.
3 - Your PO's wiring prowess.
4 - Gremlins (my favorite).
Jim

[Brian Conway]

     If the hot lead from the battery is connected to the AUX. side of the 10 AMP circuit breaker would that short it out ?  Brian

[midlife]

     If the hot lead from the battery is connected to the AUX. side of the 10 AMP circuit breaker would that short it out ?  Brian

I think they are bi-directional (like the flasher cans), but I could be wrong.  No harm in reversing the leads at this point.

[Brian Conway]

     Some of the stuff I found along the way.  A harness tag that fell out from under the dash, a C5ZZ pedal support tag ?, the flat ' D ' spot on the switch, and the 10 Amp. circuit breaker.  Brian

[jwc66k]

The C5ZZ-6501508-C is the service part number for the brake pedal support, yours may be a replacement, but without the tag, who would know. To make a "D" hole may require a two step process, drill a pilot hole, punch the "D" hole, or a single step "D" punch which seem to be unlikely as it required specials dies. Hence the instruction to "drill a hole" aka round. Convertibles used a different switch mounting.
Run a jumper to either terminal of the circuit breaker from the battery, hook a test lamp clip to the other battery terminal and place the probe on the other CB terminal. If it lights, it may be good. It makes no difference in battery polarity, positive or negative, when using an incandescent bulb type test lamp.
Jim

[Brian Conway]

     Not really interested in a ' D ' hole.  Just showing the flat part of this switch is at the bottom.  The switch tests good no matter where the battery hot lead is attached.  It also reads battery strength, 12.6 when tested with the volt meter on either post.  Brian

[Brian Conway]

OK put the whole shoot-in match back together.  Results; two hot posts on the CB.  Got a good test light at the dash harness female connection.  Connect the switch harness to the dash harness, flip the switch and the CB stops sending power to the dash harness female.  Both CB posts are still hot.  The switch does test good.  So... gotta be the CB ? Brian

[midlife]

So with the switch off, you have 12V on each side of the CB, right?  When you turn the switch on, 12V disappears on the AUX side of the CB?  Yeah, the CB is toast...it can't handle any load.  A great test would be to get a repro CB and try it in the circuit.