Hudson electrical circuit protection

]I recently added a 6-slot blade-style fuse block on my '51 Hornet coupe. I didn't like the idea of all that power going through the ignition switch contacts. So I used a relay between the ignition and the new fuse block, powered by an 8 GA wire straight from the battery (with high-power circuit breaker at the source for extra safety).

I like the fuse block style I've used on several cars, available online from Del City: http://www.delcity.net/store/6-gang-/p_10960.a_1 . It comes with all 6 fuse positions ganged together to be powered by a single 8 GA wire from the battery, and each circuit has screw terminals rather than push-on, which is more secure. It's less than $10.


I mounted the fuse block on the firewall, just on the driver's side of the heater box. Out of sight, but easy to access for fuses.

I've moved the radio, heater, A/C circuitry, and electric cooling fan to the fuse block, so I don't have to go fishing under the dash if a fuse blows.

Next I'll probably go with a relay for the headlights, as suggested. I'll probably mount it low on the firewall in the engine compartment, near the Hi/Lo Beam switch, which is where it would need to connect. In this way, I can setup the relay without ever having to get under the dash or run any additional wires through the firewall grommet(s)... just use the existing headlight switch wire terminating at the Hi/LO switch to trigger the relay, then run a large gauge wire from the batt. side of the starter solenoid down to the relay and on to the HI Beam switch.

If anyone's interested, I'd be happy to write up a wiring diagram for this.

Okay, by popular demand, here are diagrams for adding a relay-supplied fuse block, AND adding a relay to your headlight circuit. Please note the suggested parts are for 12 volt systems (not counting the fuse block, which doesn't care about voltage). If you are still 6 volt, then you'll need to source 6 volt relays and circuit breakers.. they are easy to find.

I would mount the auto-resetting main power circuit breaker near the starter solenoid and connect the power side right to the battery-side terminal on the solenoid. Keep in mind these terminals are always hot, so keep them away from any stray metal, and/or protect the terminals with a plastic cap.

Also, if you decide to do BOTH circuit modifications, it is not necessary to use a separate auto-resetting circuit breaker for each circuit. They can both be powered from the single C.B., as long as you select a 40 AMP capacity or so, should be enough to handle all the loads a 60 year-old vehicle will impose.

Geoff C., N.Z. wrote:

Sorry to be negative here, but I disagree with your siting of the headlamp relay. You are still dispersing the voltage through the headlamp and foot switch, then to the headlamps with this set-up. For maximum effect, a relay should be mounted as far forward as possible, and after the foot switch. This bypasses the switches, and applies it directly to the headlamps. If you are using the type of relay illustrated you will need two of them, one for high, and one for low beam. There is another consideration in using a relay in the ignition circuit - if the battery voltage is low, as when starting, there is a possibility of the relay dropping out temporarily. this can cause very difficult to solve starting problems. Just an old dog who has been there, done that.
Geoff

Geoff,

Thanks for your input, as your points are well taken. I see from your comment that my description wasn't clear enough. I did not reposition the wire from the ignition switch to the coil, since it is typically un-fused due to the critical need for power to the coil. I only relocated higher power components through the fuse block, such as the heater fan, my A/C harness, and electric cooling fan, among others.

Of course, there IS a downside to having any circuit unfused (such as the ignition/coil wire). I'm currently and painstakingly unwrapping the near-new harness on my '65 Corvette to remove and replace a totally fried ignition wire.. apparently it grounded out somewhere along the circuit!

And your comment regarding placement of the headlight relay is 100% spot on. I initially chose the BEFORE-dimmer switch location in my lazy effort to simplify the installation and require only one relay. My car has a new wiring harness, so I had faith in the integrity of the wiring through the dimmer switch. Yes, power does (necessarily) continue to flow through the headlight switch, but only the low-amperage power required to trigger the relay.

However, your comments forced me to ponder the lighting wiring setup on our Hudsons, and I realized that the convenient lighting junction block mounted on the driver-side radiator support (well, at least driver side for us blokes north of the equator) lends itself handily to installing two separate relays for both High and Low Beam circuits. This satisfies your suggestion of getting the higher current wiring closer to the actual headlights, plus the relays will be close to the starter solenoid as a source for the high-current power.

On reflection, this is the approach I will take with my installation, as it only requires one additional $3 relay to have a setup without compromises, and does remove the heavier current load from the dimmer switch, as well as the headlight switch.

I've taken the liberty of scratching out my best interpretation of how this should be installed. I DO want to emphasize that I am by no means an electrical expert. This schematics are merely my amateur attempt at a solution, all gained by the school of hard knocks. Use at your own risk!

JasonNC wrote:

What would the wiring diagram look like using a relay for an aftermarket A/C unit? I have a fuse box and an extra relay that I bought when I was making my overdrive wiring harness. I probably don't need to do it, but I was just curious as to how a relay to such a unit.
Thanks,
Jason

Jason,
It's hard to give a quick answer to that. My own A/C system, which I purchased from Vintage Air, came with a harness that did not include a relay circuitry. When I questioned the tech guys there, they said it wasn't needed.

In my case, I just connected my A/C unit power lead to one of the empty slots on the fuse block (one single power source is required for their system), and used an appropriately rated fuse. At least my A/C power does come from the relay-supplied fuse buss, which is fed by an 8 ga wire, more than adequate for the entire system. The supplied wire to the compressor clutch is very light gauge, so I must assume it draws a fairly low current.

I personally hate the idea of those inline glass fuses up underneath the dash somewhere (I know, that's they way the Hudson factory did it!), so I like all my power sources being at that fuse block for ease of identification and replacement.

Some A/C systems may draw higher power, and may need a separate relay for the compressor clutch, but the concept is always the same:

[ul]
[li]Connect pin 30 on the relay direct to battery source, via an ample-sized cable
[/li]
[li]Connect Pin 87 directly to the component needing power[/li]
[li] Connect Pin 86 the switch for that component (i.e., the wire from the unit which feeds directly to the compressor [/li]
[li] Connect Pin 85 directly to Chassis ground [/li]
[/ul]

Hope that's helpful.
Phil