Re-Fused

The burned wiring under the dash caused me to re-think the importance of installing a fuse panel.  The stock wiring has inline fuses randomly distributed under the dash, which is rather inconvenient.  The circuits I have added (4-way flasher, electric radiator fan, foglights, fuel pump, windshield washer pump) each need their own fuses, so I added more random inline fuse holders.

The mechanical brake light switch I installed was not adequately fused.  A short in the turn signal switch or steering column wiring resulted in the unfortunate smoky experience I documented elsewhere.   I had no problem replacing the turn signal and brake switch wiring, but with everything apart it seemed appropriate to sort out the fuses...

I established a few simple goals for designing a fuse panel for the car:

• Don't permanently change the dash, whatever is done must be reversible.  
• Provide fuse protection to key switched and unswitched circuits.  
• Use standard 1 1/4" glass fuses.  These are era-appropriate for the car, still readily available, and easier to check than more modern blade-style fuses.
• Convenient connection/disconnection of circuits without having to climb completely under the dash... which is awkward without removing the steering wheel.

With these goals in mind, I designed a clamp-on panel to attach underneath the dash, near the ignition switch, found a way to install 5 screw-type panel fuse holders, and also mount terminal strips to accommodate ring terminals to attach the wiring.

A strip of aluminum, attached to some scrap steel strap, held together with thumbscrews and clamped to the bottom edge of the dashboard under the ignition switch.  Note the headlight switch hanging in the background.

Fitting panel fuse holders.

Adding terminal strips to the steel scrap, and wiring supply side to the fuses.

If anyone is interested, here's a brief tutorial on early T-bird wiring.   

If you aren't interested, you may want to skip this part.  The headlight switch is the first stop for battery power coming into the dash.  Note that  power for heavy loads (starter, window and seat motors) don't come directly into the dash, but instead use relays.  The control circuits for those relays DO originate under the dash, however.

It should also be noted that only 3 circuits in the car have absolutely no form of over-current protection (fuse or breaker): the main starter circuit, the horn, and the cigar lighter.  To be fair, the cigar lighter has a built-in circuit breaker as part of the removable part of lighter, but nothing attached to the car.  Keep in mind that when powering other devices using the cigar lighter plug, they need to have their own internal fuse!

The headlight switch has two 20 amp circuit breakers in it: one for stopl/tail/parking lights and the clock, the other for headlights.  It also has a 9 amp fuse for the courtesy light.  None of these circuits rely on the position of the ignition switch.  Unswitched battery power (always a yellow wire) is fed from the headlight switch to terminal B of the ignition switch. Terminal C ("on" and "start" position only) is connected to the ignition and the idiot lights, and terminal S ("start" position) is connected to the starter solenoid.  All other circuits are connected to terminal A ("accessory" and "on" position).

Wiring up the Panel

I carefully mapped these circuits, along with all the circuits I have added to the car, to the new fuse panel.  I decided to take power from terminals B (yellow, unswitched) and A (red, "acc+on") of the ignition switch, and wire these through the appropriate fuses to the terminal strips.  Note that the 4-way flasher, stoplight, and backup light circuits are unswitched... I wanted them to work even if the ignition was off.

Mapping key circuits to the 5 fuses I have available on the panel.

Labeling the panel came in handy when wiring it up.

The panel detaches from the dash, and hangs down conveniently exposing the  terminal strips.
Note how each circuit is identified with silver sharpie on the heat-shrink insulation.

 I have invested in a good set of wire stripping and terminal crimping tools, and a heat gun.   This made quik work of reterminating each of the circuit wires with the appropriate lug and heat-shrink insulation.  I made sure there was room for all of the wires under the dash, and nothing would short out to the ignition switch terminals, then carefully connected it all together and clamped the panel in place.

With the panel clamped under the dash, it seems like a lot of extra wires under there... but in fact it is much easier to identify and isolate any particular circuit.  It is also very convenient to have all the fuses available in a single location!

Was it really worth the effort?  Well, probably not... the panel is completely invisible unless you deliberately look under the dash.

This effort has, however, helped restore my confidence in the car's wiring.  That is certainly worthwhile.  Just because something isn't immediately visible doesn't mean it isn't important.