What is the 3 amp fuse in a 1969 Roadrunner for?

[insidegroove]

When i test all the fuses with a test light, i have two 20 amp fuses that are hot all the time, three that are hot when i turn the key.....then there is a 3 amp fuse on the far right that doesn't make the test light light up when the key is on or off? anyone know what that fuse is for and why i dont have power to it?

 

[Carl Ray]

Feeds instrument panel lights. Turn headlights on and recheck.

 

[insidegroove]

i tried last night......still no luck. i seem to have alot of issues going on with instrument lights and gauges so i pulled the whole gauge cluter out today and im going to attempt to test it all tonight. hoping theres a youtube video out there breaking down a 1969 instrument cluster test

 

[Carl Ray]

Likely an issue with dimmer switch. Ceramic gets old and brittle. Let us know what you find.

 

[V.R.D]

i tried last night......still no luck. i seem to have alot of issues going on with instrument lights and gauges so i pulled the whole gauge cluter out today and im going to attempt to test it all tonight. hoping theres a youtube video out there breaking down a 1969 instrument cluster test

read the factory service manual it tells you how to test and fix.

 

[insidegroove]

some great progress with the instrument cluster. seems over 53 years there was some slight pitting and surface rust, dust etc all over the circuit board. i carefully cleaned the entire board, cut some new transparent green and blue plastic for the directional indicators and the high beam indicator and used all new bulbs and sockets. every light on the cluster is now working!!! i also tested the fuel gauge while i have the cluster out on my bench.......the gauge maxes out to full when i ground it so i now know the gauge is fine and it must be the sending unit. im hoping with everything working on the instrument panel now, when i put it all back together the dimmer switch works but time will tell. right now im carefully cleaning and repainting everything inside the cluster so it will look like new

 

[insidegroove]

so many electrical gremlins with this car i dont even know where to start ugh! so i had the cluster out for a 4th time this week.....i decided to clean the whole thing up like new, nice new black and silver paint, painted the needles bright orange like original, all new indicator bulbs and sockets, put new indicator color plastic (green for the turn signals and a blue one for high beam indicator). the cluster looks outstanding. i tested all the little metal prongs on the back of the cluster.....the instrument lights lite up, the high beam indicator, turn signals etc. then i tested the fuel gauge....the needle shot up to full and then a tiny bright spot and poof.....i think i fried the fuel gauge in the 10 seconds or so i ran power too it. i will have to replace that now. then i reinstalled the cluster back in the car and just like before, the only indicator lights i can get working while its in the car are the turn signals/emergency flashers. no other lights will come on even though they work on a bench test. i then took the cluster back off again and tested the 9 wires coming up to the cluster......the dark blue one with the white stripe that says its the feed wire in my owner's manual is the only one showing a reading on the meter (12.47 volts). the rest show zero. is this part correct or should any of these other wires be showing a reading? i then went back to the fuse issue (no reading on the 3 amp fuse on the far right). i followed one wire (tan) from the fuse to the dimmer switch, and the other wire (orange) that travels up to the instrument panel and is supposed to light the instrument lights, and that same wire splits off to the radio (orange, red and white). So i have a few questions if anyone can answer.....to rule a few things out. i have seen other instrument clusters online that have a black wire coming from the voltage limiter to a small cylinder that looks almost like a AA battery, mine doesnt have this. is this why some of my lights wont work??? also, i have purposely left a few of the bulbs out (temp warning and oil warning lights).......does not having these sockets/lights installed on the circuit board prevent other lights from working? (i doubt this because the turn signal lights are working).

i DID do a small test on the dimmer.......while moving the dimmer wheel around at a few points here and there i got 12.4 volts, but it was sporatic. my thinking is the tan wire coming from the dimmer is the feed for the 3 amp fuse......and may be preventing the power to go to the orange wire that should light the instrument lights???????

 

[Carl Ray]

See Post #4. Dashlight issue is most likely dimmer switch as you have discovered. You are chasing your tail pulling the cluster in and out. Not all wires on the 9 pin connector are power wires. Most are signal wires, so they are looking for a ground via the oil sender, fuel sender, temp sender, etc.

The voltage limiter has no impact on the dash lights, its purpose is to drop voltage down from 12 volts to 5 volts for the Temp/Fuel gauge. The round cylinder attached to the power out side of the voltage limiter is a capacitor. Its function is to smooth out the voltage pulses. It is not technically needed. If used it must e hooked up properly, or it can cause the gauges not to work. Not sure why you are still grounding the fuel gauge wires, you already found the problem with the wire from the kick panel to the sending unit, you just need to fix it. Regarding the burnt gas gauge, did you apply 12 volts directly the terminal at the back of the gauge and then ground it? If so, you sent double the voltage thru the gauge, and while solidly grounded you most likely burnt it up. Temporarily grounding the sending unit is fine, but leaving it on for any period of time will send too much current through the gauge and fry it.

 

[insidegroove]

just so you guys don't think I'm a total moron, i carefully took apart the dimmer switch last night......cleaned the entire thing. all the metal is shiny again...all the contact points are clean. still no lights this morning. i did a continuity test this morning.....from the tan wire at the dimmer switch to the tan (bottom) side of the 3 amp fuse and it was getting a signal. So i then did a continuity test from the orange wire that plugs into the back of the gauge cluster to the orange (top) side of the 3 amp fuse and it also gets a signal. my thinking after studying the wiring diagram is that the instrument lights should be getting power from the tan wire coming from the dimmer switch and feeding that power up to the instrument lights via the orange wire. am i wrong? im still stumped. im considering just setting up a toggle switch by splicing into the headlight on/off that will light up the instrument lights and my aftermarket gauges under the ashtray and call it a day

 

[Carl Ray]

The wires have continuity which is good, but the dimmer needs more than cleaned. They are notorious causing problems after 50 so years. Take a look at this guys listing on Ebay. He's a good guy from another b body site. He redid my dimmer switch and all is good. Do not buy a new replacement, have yours fixed.

1968 68 69 70 Dodge Coronet Charger Dash Dimmer Switch Rebuild Service | eBay

Find many great new & used options and get the best deals for 1968 68 69 70 Dodge Coronet Charger Dash Dimmer Switch Rebuild Service at the best online prices at eBay! Free shipping for many products!

www.ebay.com

You could probably ask him a few questions via Ebay and he'll confirm the cause of the issue you are experiencing.

 

[insidegroove]

The wires have continuity which is good, but the dimmer needs more than cleaned. They are notorious causing problems after 50 so years. Take a look at this guys listing on Ebay. He's a good guy from another b body site. He redid my dimmer switch and all is good. Do not buy a new replacement, have yours fixed.

1968 68 69 70 Dodge Coronet Charger Dash Dimmer Switch Rebuild Service | eBay

Find many great new & used options and get the best deals for 1968 68 69 70 Dodge Coronet Charger Dash Dimmer Switch Rebuild Service at the best online prices at eBay! Free shipping for many products!

www.ebay.com

You could probably ask him a few questions via Ebay and he'll confirm the cause of the issue you are experiencing.

awesome thank you!!

 

[Russ69Runner]

That switch can be a problem for sure. I cleaned mine and it worked like it should with contact cleaner. Ben awhile since I put the car together and know that wiring is a test of nerves. Don't give up just yet. Walk away and take a deep breath. You will get it. Don't over think the problem.