INST Fuse blowing

-
moparmandan

moparmandan

FABO Gold Member
FABO Gold Member
Joined
Jun 28, 2017
Messages
2,999
Reaction score
3,009
Location
Deland, FL
Put our cluster back in after wiper refurb and cluster refurb. All other cluster lights work. Connected the battery turned on the running lights and checked for instrument lights, nada. Found the fuse blown. Turned off lights and replace the fuse, blew again. Got handfuls of fuses so tried another one and it worked for a while figured it was cheap Chinese fuses. Try it again later to show off our handiwork to someone and it blew again. What do y'all think? What else could be loading up the orange wires? Or could it be from the headlight (tan wire) switch side? Where else do those orange wires go? Oh yeah, 1973 Scamp. Thanks for the help
 
Most likely in the orange wires, here is how this works:

The dash dimmer actually GETS power from the tail light / park circuit fuse, so that circuit must work "first"

That power goes through the dimmer, "out" on the tan, and TO the instrument fuse via the tan wire, then out to all dimmer controlled lighting on the orange.

Since there are quite a few, you hope for "luck." Since you meddled with the cluster, I'd start there. Perhaps you have a lamp or socket screwed up in the cluster, or pinched something in the harness getting it back in

If you have a column shifter quadrant I'd check that, the ashtray if equipped, and from there ??

What else did you move/ work on?
 
67Dart273 said:
Most likely in the orange wires, here is how this works:

The dash dimmer actually GETS power from the tail light / park circuit fuse, so that circuit must work "first"

That power goes through the dimmer, "out" on the tan, and TO the instrument fuse via the tan wire, then out to all dimmer controlled lighting on the orange.

Since there are quite a few, you hope for "luck." Since you meddled with the cluster, I'd start there. Perhaps you have a lamp or socket screwed up in the cluster, or pinched something in the harness getting it back in

If you have a column shifter quadrant I'd check that, the ashtray if equipped, and from there ??

What else did you move/ work on?
Click to expand...
Only everything. Thanks bud. Glad you're online. Like I said we took the radio and cluster out to replace the wiper pivots, took the cluster all apart. Cleaned it up, new bulbs. Bench tested all the circuits with a 12 volt power supply before we put it back together. All the lights worked. Also have a new headlight switch. Put a new radio in but have not wired it yet.
 
By the way never had dash lights before. Also we dropped the column to get the cluster out.
 
Place a test lamp across the fuse socket that keeps blowing. When the short occurs the lamp glows BRIGHT, when normal current flows the lamp is dim, or no glow at all.
While you are looking at the test lamp gently wiggle harnesses and wires, dimmer, etc and try to get the lamp to glow bright.
Not only saves fuses, but is gentle on your harness and circuits while you troubleshoot.
 
billccm said:
Place a test lamp across the fuse socket that keeps blowing. When the short occurs the lamp glows BRIGHT, when normal current flows the lamp is dim, or no glow at all.
While you are looking at the test lamp gently wiggle harnesses and wires, dimmer, etc and try to get the lamp to glow bright.
Not only saves fuses, but is gentle on your harness and circuits while you troubleshoot.
Click to expand...
Thanks for the reply. Do you mean one of those ice pick looking test lamps or a light socket with alligator clips? I kind of like the light bulb socket with alligator clips idea.
 
I actually made my own soldering wires and clip leads across a 12V bulb, but yes you can buy at ye ol'O'Rielly auto parts a test lamp with back probe and clip lead. Just some sort of 12V lamp across the blowing fuse location to allow a visual aid to troubleshoot and be gentle to the circuit during short conditions.
 
Well you need a lamp that draws some current. A typical store bought test lamp may or may not do what you want, and an LED tester will just light up bright. Something I use A LOT is an old stop / tail light socket with an 1157 bulb

2.jpg


You can use these (as in the above post to replace fuse) to find shorts, I used to use them to limit current flow when charging small lead batteries (bike) from an oversized charger

====================================

You have a socket (ground)

One wire is tail (less wattage, lower current, dimmer filament)

Second wire is stop (more wattage, more current, brighter filament)
===================================

You can wire this several ways:

A....Least wattage least current is to use the two wires to connect, leave the socket unconnected. You want to make sure it does not contact anything, IE tape it

B....Next bigger wattage, a bit more current, is to use the socket for one terminal and the tail wire for the second terminal

C....Next larger after that is to use the socket for one terminal, and the stop lamp filament for the second terminal

D....For a large load, you can use the socket for one terminal, then twist the two wires together and use both of them together for the second terminal, which of course lights both lamp filaments
 
67Dart273 said:
Well you need a lamp that draws some current. A typical store bought test lamp may or may not do what you want, and an LED tester will just light up bright. Something I use A LOT is an old stop / tail light socket with an 1157 bulb

You can use these (as in the above post to replace fuse) to find shorts, I used to use them to limit current flow when charging small lead batteries (bike) from an oversized charger

====================================

You have a socket (ground)

One wire is tail (less wattage, lower current, dimmer filament)

Second wire is stop (more wattage, more current, brighter filament)
===================================

You can wire this several ways:

A....Least wattage least current is to use the two wires to connect, leave the socket unconnected. You want to make sure it does not contact anything, IE tape it

B....Next bigger wattage, a bit more current, is to use the socket for one terminal and the tail wire for the second terminal

C....Next larger after that is to use the socket for one terminal, and the stop lamp filament for the second terminal

D....For a large load, you can use the socket for one terminal, then twist the two wires together and use both of them together for the second terminal, which of course lights both lamp filaments
Click to expand...
GREAT IDEA. A 1157 socket+bulb with two filaments is great. I should have thought about that, and YES the LED test lamp is crap and does not work in this condition.
 
Thanks guys. I've got extra sockets and bulbs. I'll rig up a test light tomorrow and let you know what I find. Just for reference what is that strange symbol on the wiring diagram that the orange wires run into and then it looks like radio wires come off of that. Red and white wires running to it also. Is that a splice or something?
 
Likely the radio connector. Will have an orange for the radio dial lamp, and a red for power.

What diagram you looking at? Factory service manual? Or "MyMopar" aftermarket diagram, or something else?
 
moparmandan said:
Put our cluster back in after wiper refurb and cluster refurb. All other cluster lights work. Connected the battery turned on the running lights and checked for instrument lights, nada. Found the fuse blown. Turned off lights and replace the fuse, blew again. Got handfuls of fuses so tried another one and it worked for a while figured it was cheap Chinese fuses. Try it again later to show off our handiwork to someone and it blew again. What do y'all think? What else could be loading up the orange wires? Or could it be from the headlight (tan wire) switch side? Where else do those orange wires go? Oh yeah, 1973 Scamp. Thanks for the help
Click to expand...
Had the same problem,Found and installed a correct 3 amp slo burn fuse.haven't had a problem since.The brand of fuse is Littel Slo Blo Fuse
 
67Dart273 said:
Likely the radio connector. Will have an orange for the radio dial lamp, and a red for power.

What diagram you looking at? Factory service manual? Or "MyMopar" aftermarket diagram, or something else?
Click to expand...


67Dart273 said:
Likely the radio connector. Will have an orange for the radio dial lamp, and a red for power.

What diagram you looking at? Factory service manual? Or "MyMopar" aftermarket diagram, or something else?
Click to expand...

This:

6493035-WiringDiagramFullValiantDuster-2.jpg


What's this?

Capture9.PNG
 
Yeh. Radio connector. That is not a factory diagram, and they leave stuff out. Those ARE easier to follow sometimes. You should go to MyMopar and download the factory manual. There is a chart on past the diagrams which details all/ most of the connectors. Unfortunately the 73 book IS more difficult in some ways, but you do need it for some details. The diagrams show the radio, it's power connector is "CI-13" which means "Connector, Instrument, no. 13" That part is at coordinates D-38, page 8-163. Then you go back to the connector charts and find CI-13 which is the connector drawing itself That is page 8-168

radio2.jpg


radio1.jpg
 
Last edited:
If you can't run this down, and confirm it is on the orange wiring side of the fuse, I would just cut one at a time until the short goes away, hook them up except of that and then figure out what is not working.
 
67Dart273 said:
Yeh. Radio connector. That is not a factory diagram, and they leave stuff out. Those ARE easier to follow sometimes. You should go to MyMopar and download the factory manual. There is a chart on past the diagrams which details all/ most of the connectors. Unfortunately the 73 book IS more difficult in some ways, but you do need it for some details. The diagrams show the radio, it's power connector is "CI-13" which means "Connector, Instrument, no. 13" That part is at coordinates D-38, page 8-163. Then you go back to the connector charts and find CI-13 which is the connector drawing itself That is page 8-168

View attachment 1715186290

View attachment 1715186291
Click to expand...

I've got the FSM. I'll go check it out. Thanks!
 
67Dart273 said:
If you can't run this down, and confirm it is on the orange wiring side of the fuse, I would just cut one at a time until the short goes away, hook them up except of that and then figure out what is not working.
Click to expand...
Makes sense. I'll do it if it comes to that.
 
Worked on the car a little bit this afternoon. Here's what I have. With running lights on. Got a bright dimmable test light across the inst fuse slot. Checked orange wires to ground with multimeter. Dead short. Cut 1 loose. That wire dead short to ground. Check the other orange wire, short to ground. Checked tan wire with test light to ground bright light.

Pondered it for a little bit went back to check voltage on tan wire. Nothing. Scratch my head. Ask my son if we had tail lights. Nope. Check tail light fuse. Good. I said oh boy here we go. Came in to eat dinner. Haha. What do you guys think?
 
You have power both sides of fuse? That fuse should be hot both sides at all times.

"It's possible" you damaged the dimmer control

Depending on your meter, measuring the oranges to ground might show what you think is a short because the lamp bulb filaments are such low resistance.

This in part is why I suggested the tail lamp lashup above. It draws enough current that if you hook power to one end and the dash lamps (one of the orange wires) to the other, it will LIGHT those lamps while itself is glowing "at some brightness". But if one is actually a dead short, all that lamp will do is light up full brightness.

In other words you need a test lamp that draws enough current to "sort of" operate the load you are testing. The fact that you are using a 12V test lamp means that if you hook it to a short, all it will do is to "light up."

You could even use a headlamp for this, which draws more yet.

Probably an even better way of looking for this now that you have separated part of the orange.........is to connect a test lamp to power on one terminal of the lamp, and with the INST fuse pulled, hook the other terminal to the orange side of the fuse clip. This will of course feed power to the orange side and you can go from there.
 
If it helps to "un-discourage" you some, a circuit with multiple loads, and an intermittent are a couple of the hardest types of problems. Stay with it, the fact that you are willing to get your hands dirty is most the battle LOL
 
67Dart273 said:
You have power both sides of fuse? That fuse should be hot both sides at all times.

"It's possible" you damaged the dimmer control

Depending on your meter, measuring the oranges to ground might show what you think is a short because the lamp bulb filaments are such low resistance.

This in part is why I suggested the tail lamp lashup above. It draws enough current that if you hook power to one end and the dash lamps (one of the orange wires) to the other, it will LIGHT those lamps while itself is glowing "at some brightness". But if one is actually a dead short, all that lamp will do is light up full brightness.

In other words you need a test lamp that draws enough current to "sort of" operate the load you are testing. The fact that you are using a 12V test lamp means that if you hook it to a short, all it will do is to "light up."

You could even use a headlamp for this, which draws more yet.

Probably an even better way of looking for this now that you have separated part of the orange.........is to connect a test lamp to power on one terminal of the lamp, and with the INST fuse pulled, hook the other terminal to the orange side of the fuse clip. This will of course feed power to the orange side and you can go from there.
Click to expand...
Thanks a lot for your help. I'm using a good fluke multimeter.
I should clarify. The test lamp I'm using is an 1157 light socket like we had discussed using the two wires but not the socket. And yes it would light up bright but is dimmable when connected across instrument fuse slot. Until we lost tail light power.
 
Last edited:
BTW thanks for the moral support. But I'm not discouraged yet. I didn't come this far fighting the electrical gremlins in this car to give up now. LOL. This is really the last of the electrical issues even with the loss of tail light power. It's not going to beat me.
 
You must log in or register to reply here.
-

Back
Top