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Fusible links or maxi fuses


ralphnof49

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After looking at a pre 1967 Corvette with wiring melted I began to wonder if our old Lincolns need more protection. My 1947 has circuit breakers for the lights and a breaker for the window hydraulic system, but does it need more protection for the ignition system and the horn relay? Opinions please. I am going to add protection for my 1961 Corvette.

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I've gone the opposite direction from 19tom40. After spending my working years doing electronics and process control I added fuses and relays to my wiring circuits. I relealized years ago that if a piece of equipment was expensive it had fuses. Mine are hidden inside the dash but easy to get at for replacement. I received this car from a PO who did a very amateur rewire and didn't know what he was doing. I've cleaned up all I could find but who knows what I may have missed. I will also install a fuse link to the generator also.

I just returned from the Turkey Run in Daytona. I looked at a very nice large formal sedan (I think) that had a very nice front end to about the fire wall. Then a nice rear section. The rest was just the frame. Don't know why the passenger compartment went up in smoke but it did.

Edited by Beltfed (see edit history)
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I guess I should have given more of an explanation of why I don't believe in adding fuses, with the one exception of the cigarette lighter. I believe that a fuse should be in that circuit or the lighter disconnected.

 

A 6 volt system has problems when the voltage drop in a circuit reduces the voltage below the optimum operating voltage for the circuit. Each connection adds some resistance in the circuit, so when you install an additional fuse in a fuse holder, you add 4 connections, each of them with some resistance. Depending upon the current in the circuit, the drop across the fuse circuit could be around 0.1 volts. The headlight circuit would be a good example.

 

A typical light switch in very good condition, will have a 0.1 voltage drop, the dimmer switch, also in very good or new condition, will have another 0.1 voltage drop. The circuit breaker adds another 0.1 drop and the wires and other connections will add another 0.2V drop. So if your battery is at full charge of 6.5 V, your headlights see 6.0V. That is a good voltage for the bulbs and they will shine bright at about 90% of full brightness. Now as the light switch gets older, it can drop as much as 0.3V and the dimmer switch as much as 0.5V. Now your bulbs see 5.2 V and are about 60% of the stated output. Add to this the poor reproductions of the bullet connectors and your lights could see another drop of 0.3 and you will have very marginal headlights. The light output of an incandescent bulb drops in a geometric progression as the voltage decreases.

 

 

The best insurance against a fire is a good wiring harness, with few connections in each circuit and each connection is in good condition.

 

I like Narragansett Reproduction wire harnesses, because they solder each bullet, spade and ring connector, and their wires are the same gauge as the original. Rhode Island is another good supplier. I have not found a good supplier of the bullet connectors.  Depending on location, they last between 5 -10 years. The ones in the engine compartment fail first due to the rubber sleeve deteriorating from the heat.

 

I check the voltage drop in the high current circuits every Spring and do a visual inspection of all connections. I find that 1 or 2  connectors have failed. My Lincoln still has all of the Ford supplied connectors and they are still in good shape after more than 60 years.

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Thanks to both for your thoughtful comments. For sure good wiring and connections are most important. The point about the cigarette lighter is one we should all check out. Tom please explain how you check voltage drop so we can do it right since greater resistance can cause wires to heat. The high current circuits would include lights and horn and generator I assume- any others to check.

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 The voltage drop can only be made when the circuit is loaded (ie: starter turning, headlights on, solenoid picked, etc). To check the voltage drop in a positive ground circuit:

 

Connect the COM (black) lead of your meter to the NEG battery post and the POS (+ or red) lead to the load (headlight)

Activate (turn the lights on) the load and read the meter.

The reading for the headlights should be less than 0.5V, Typical on my 2 cars is 0.3V.

 

Next connect the red lead to the POS battery terminal  and the black lead to the grounding connection at the load

Activate the load and read the meter

The reading should not be more than 0.1 V. Typical reading on my 2 cars is 0.03V

 

The reading for the starter circuit should be 0.3V or less for the supply side and  almost 0V for the grounded side.

 

To check in a NEG grounded system, revrse the meter leads.

 

The generator circuit has  a connection at the generator and another at the voltage regulator. Correct gauge wire is important here. The current in the circuit varies too much to be able to give reasonable voltage drop readings.. The grounding of the generator and regulator is very important and can be checked with your Ohmmeter. Disconnect the grounded battery cable and measure between the cable at the battery end and the case of the regulator and generator.

 

These readings are valid with a fully charged battery and may be different with a partially charged battery.

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