Help needed #5 5A Fuse location

[PLY478]

Working on a 1974 Challenger here.

Wondering if anyone ever came across this?

On the fuse holder, the #5 Fuse, tested with a test light, has NO power on either side of the fuse.

All other fuse's and terminals tested out just fine.

I need to start here as this fuse controls the Dash lights.

Your help would be appreciated.

Thanks
PLY478

 

[72RoadRunnerGTX]

The 5 amp fuse is the dash illumination circuit. Fed from the headlight switch via the dimmer, turn on your headlights if you want to see voltage there.
If the dash lights are not working with the lights on, will need to troubleshoot the dimmer or headlight switch

 

[PLY478]

OK that helps. Head lights work, both low and high beams. (Dimmer switch) Dash lights or floor high beam dimmer?

 

[72RoadRunnerGTX]

Dash light dimmer.

 

[PLY478]

Thanks

 

[pschlosser]

With age, the dimmer gets (electrically) noisy and oxidized. I find turning the dimmer fully on and off, several times, can clean up the internal connections enough to see dash illumination function. Removing and cleaning the (internal) rheostat with contact cleaner is ideal, but a small chore to remove the switch and disassemble it.

 

[PLY478]

Ok had some time tonite without being rushed. Took the switch panel out, cleaned up all the connections, even the dimmer rheostat. I then hooked up all four switches to the plugs there’s rear defrost.

Conclusion; with the headlights on there is still no power on either side of the fuse holder on fuse number five.

 

[72RoadRunnerGTX]

Did you check voltages at the headlight and dimmer rheostat? Check for 12v at terminal R of the headlight switch (black with yellow tracer) with the switch on, (park or headlights). Check for this power at the dimmer rheostat (black with yellow tracer). Then you should have variable voltage at the tan wire coming out of the rheostat. The tan wire goes to the fuse holder in question in the fuse box.

 

[PLY478]

Did check voltages at the headlight and dimmer rheostat?

No… although I will if time allows tomorrow.

Thanks for your insight here.

 

[PLY478]

So I took apart the dash dimmer switch…

Cleaned and lubed.

On the bench I hooked up 12v to terminal “I”

Before cleaning and lubrication I did not have power at terminal “R” I now have power there and it dims my test light.

Although no power at terminal “D”

Once the porcelain depresses, the copper strip to the back of the terminal I can ohm that and a connection is being made. Is that fed from another power source in the harness?

 

[72RoadRunnerGTX]

The power to the dimmer comes in to dimmer terminal I from the headlight switch (terminal R) on a 18ga black with yellow tracer (Circuit id L6A-18BL/Y*). Will have full line/battery voltage but only with the switch in park or headlights position. Have you verified this power is present with the lights on? The variable voltage then leaves the dimmer on terminal I and goes to the fuse box on a tan wire, circuit id E1-18T. From the fuse its off to the lamps on orange wires.

 

[PLY478]

Also have 10.7 V at the “R” terminal with the head lights on.

And 10.7 V at the dimmer B/Y wire.

 

[72RoadRunnerGTX]

Try jumping the dimmer switch plug terminals I & R together, see if you have battery volage at the inboard fuse clip with the lights on.

 

[Challenger RTA]

Ok sorry to butt in. But GTX knows what is doing. Try this short cut. PUN?! From the Battery or ACC terminal jump power to any side of the fuse. See if you have dash light. that will confirm if the circuit is good or bad. If not it's the bulbs or grounds. There's a little more to it than that.

 

[Challenger RTA]

Here is something to look into while you at it. Dash lights a Brighter possibility

 

[Litchkar]

OK that helps. Head lights work, both low and high beams. (Dimmer switch) Dash lights or floor high beam dimmer?