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Tapping the ignition feed in 1970s cars

I installed a DRL setup on the Duster the other day, and found there was no pre-existing feed from the run side of the ignition switch heavy enough to power it.

In studying the fuse block of a 1974-76 A-body Mopar, you will discover that the only fuse that is hot in the run side of the ignition switch is number 6 and it’s only 3 amps, fine to power a tachometer or other gauge, but not nearly enough to power an accessory such as a DRL or electric fuel pump that only needs power when the engine is running. One can always tap off the J2 circuit with an inline fuse, but I prefer to keep the fuses in one spot wherever practical.

G5 circuit

In further study of said fuse block, one finds that the number 5 fuse was never used, and actually has no clips to hold a fuse. Not a major problem if one has a spare wiring harness around, the clips can be removed from the other fuse block. They might be available new somewhere also, if someone knows where these can be found new please let the rest of us know.

To remove the fuse clip from the fuse block, from the top (fuse) side of the block use 2 small screwdrivers or picks to push in the tabs on the sides of the fuse clips, then push the clip out the back of the fuse block. It seems like it takes 3 hands and a bit of luck to get them out, but with some practice one can remove them without damaging them.

fuse clip - Valiant

The picture shows a fuse clip that the wire connector is broken off of, but it’s the last one I have left (time to acquire another used wiring harness) after setting the fuse block on the Trailduster on fire a few years back, but you can see the tabs clear enough. (One note about fuses, never replace a fuse with a penny, besides ruining the penny, you waste a few dollars.) Just about any Mopar fuse block from the 70s uses the same style of clips, so scrounging used ones shouldn’t be too hard.

While you have it out it is easier to clean any corrosion off that might have accumulated over the past 3 decades. If it’s not to bad electrical contact cleaner will do the job nicely, if it’s rusty it might require scraping the fuse contact area with the tip of a knife.

Plymouth Duster fuse block

dodge dart fuse block

clip holds wires to fuses

Ma Mopar might have had another fused ignition circuit in mind, as the feed (circuit J2B on the wiring diagram) from the ignition switch for fuse 6 is a 14 gauge wire, way more than the 3 amps for the gauges requires, so the feed for your new fuse simply needs to be spliced to it. It’s the larger of the blue wires with a white tracer. Make certain if using a used fuse clip that the attaching wire is heavy enough to run the accessories you plan to hook to fuse 5. I prefer to solder the connection, and then tape it securely, although I have heard positive reports on Posi-Taps.

fuse splice for ignition feed tap

To install the new fuse clips in the fuse block, simply push them in from the back of the fuse block until the tabs are snapped securely in place, and route the wires out of the holder on the side of the fuse block. To keep the system the same as the rest of the fuse block, install the clip from the J2 circuit toward the center of the fuse block.

fuse block with ignition feed

The fuse block is marked with 20 amps for the number 5 position, but as I was running a DRL setup off it that called for a 15 amp fuse, that’s what I installed in it. None of the fuses are marked with what they run, so I keep a chart in the glove box, and noted on the chart that number 5 was 15 amps for the DRLs. (Also see valiant.org’s Valiant - Duster - Dart fuse and bulb chart.)

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