Instrument panel Light dim issue Valiant 1965

[Leos Luis]

Hello folks, I need your help to figure out what might be going on with my 1965 Valiant.
I replaced the 3 bulbs that light up the instrument panel — I removed the original bulbs and installed LED ones. Everything was fine up to that point.

The problem starts when I turn the headlight switch knob to the left to turn on the interior courtesy light — at that point, a short occurs and blows the fuse.
I installed a new headlight switch, but the problem remains: the fuse blows when turning the dimmer on the switch.
I reinstalled the original bulbs (no more LEDs), but the problem continues.

I also noticed that the fuel and temperature gauges stopped working.
I checked the wiring, and everything seems fine at first glance.

Any ideas what could be causing this issue?

 

[66Valiant528]

If you did not have the battery disconnected when you pulled the cluster you probably shorted out the the gage that has the voltage limiter built into it.

 

[Mattax]

Hello folks, I need your help to figure out what might be going on with my 1965 Valiant.
I replaced the 3 bulbs that light up the instrument panel — I removed the original bulbs and installed LED ones. Everything was fine up to that point.

The problem starts when I turn the headlight switch knob to the left to turn on the interior courtesy light — at that point, a short occurs and blows the fuse.
I installed a new headlight switch, but the problem remains: the fuse blows when turning the dimmer on the switch.
I reinstalled the original bulbs (no more LEDs), but the problem continues.

I also noticed that the fuel and temperature gauges stopped working.
I checked the wiring, and everything seems fine at first glance.

Any ideas what could be causing this issue?

Can't solve your problem but can tell you how to find the problem. Narrow down the problem by following the circuit in question.
Side note, most LEDs are not dimmable.

The headlight switch is a multi-switch with three circuits going through it.
The dome light gets grounded by the headlight switch when the knob is turned all the way.

The headlights are powered from terminal B1 to H and there is a 15 amp circuit breaker. Most replacements have a 20 amp circuit breaker so try to use the original.

The parking lights and the instrument panel lights are powered from terminal B2.
B2 gets its power from a fuse in the fusebox. Some other circuits may also use that fuse.

Inside the headlight switch, power from B2 is branched off. One branch to the parking and tail lights. The other branch to the rheostat for the instrument and radio lights. The instrument lighting power then goes back to the fuse box to a 2 amp fuse before going to the lamps.

Begin at fusebox. Identify which fuse has blown. A short will be downstream of that fuse. If you have multi-meter or test light you can disconnect the battery and check for shorts. Isolate sections of the circuit by disconnecting connectors as needed.

Power is supplied like this -
Battery or alternator to main splice. Then from main splice to two or three fuses. Two or three other fuses get power through the key switch, and one for the instrument lights gets power through the dimmer on the headlight switch.

 

[Mattax]

Fuel and temperature gages are powered from either the 'run' circuit or the switched accessory circuit. The diagrams in the '65 Service manual will show which one.
The power for both is reduced by an instrument voltage regulator. There's a good 1960s Master Technicians Conference explaining how they work. Do a search - its been posted on FABO many times.