Stop and Interior 20A fuse keeps blowing

[Mariposa Mike]

A new to me 66 Charger has several electrical issues including the stop and interior lights 20A SFE fuse blowing. Does not happen immediately but after my wife was pressing on the brake pedal with the door open it eventually went kaput. The only other thing she did was press on and release the E brake. That light stays on so no short there. Since there are 6 lightbulbs across the back and 4 more in the interior, is it possible there is too much load on the one fuse? I'm also having other problems with electrical such as no horn and emergency flashers not working. Also the starter is not always working but I have power to the starter relay so it might be the relay. Previous owner replaced the starter with a high torque (smaller) unit and that looks to be recent. I think he might have been chasing some of these issues since I am finding lots of spare fuses, ballast resisters, and such. Oil pressure gauge not working either and he has a spare module for that from MEGA parts. Any idea on what might be happening to the light circuit? Previous owner passed away so no help there.

 

[R413]

A quick way to tell if you have a wiring or socket problem, or if the bulbs are drawing too many amps? Remove all the bulbs and activate all of the circuits like you did before, the current is in the wires and shorts will still blow the fuse with the bulbs out.

 

[twecomm]

From shop manual : The correct fuse rating for the tail, stop and dome lights fuse is indeed a 20 amp rating. You should not assume that all the correct lamps are installed in your car. First thing to do is check them all to see if correct. The six tail light bulbs should all be #1034's. Amber front park and turn signal lamps are also # 1034's. The four interior dome lamps should be #1004's.
Looking at the specs on all the lamps, at 12.8 volts, the #1034's are dual filament lamps, the lo brightness filament for tail lamp function is .59 amps each. Add in the two front #1034 amber park lamps, that's another .59 amps x 2, so that's a total of 4.72 amps with parking lamps on.
The filament for the hi brightness turn signal / brake filament is 1.8 amps each. So with brakes applied, six rear bright lamp filaments lit, that's another 10.8 amps. The # 1004 interior amps are .93 amps each. If all the lamps are correct and indeed getting the correct voltage, they should NOT be taking out a 20 amp fuse. You will need to check the wiring for possible shorts by removing ALL the lamps ,rear, front and interior as well as the 20 a fuse. Check with ohm meter at load side of fuse block and see if there might be a partial short somewhere.

 

[Mariposa Mike]

I will check the bulbs but I don't understand what I should see or not see by checking the load side of the fuse block, which I guess is the side power is coming in? One probe to ground and one to the load should read ????? If voltage is there how does that relate to ohms? Or an open circuit? Sorry to be so dense but I'm a bit out of my element and willing to learn. Volts I understand but not ohms other than to check resistance of spark plug wires. And I appreciate the feedback from both of you. Gives me hope.

There are many wiring issues with this car and I will have to check numerous wires/circuits. I was also thinking maybe the firewall wiring blocks where they go thru to the interior might be shorting or have corrosion. Seems I have heard about that before on MOPARS but could be wrong. Really won't be able to see much on the interior of the dash without removing the gauge panel so hopefully the issues are outside of that. This is an A/C car so a lot that hardware is in the way.

 

[twecomm]

Chasing electrical problems in these cars can be tricky.. If you remove all the bulbs mentioned in my previous post in the circuit you are having a problem with, there will be no loads. If the 20 amp fuse for that circuit is REMOVED at the fuse block, you would want to verify with a DC voltmeter which side of the fuse holder is the battery voltage and which side is the load side. Double check there is no voltage present on the load side. To be safe, I would suggest disconnecting the battery at this point. Should something you accidentally do with working on wiring or electrical system, you could do some damage. You don't need to create new problems ! if your car is equipped with 4 way flashers that switch should be in the off position.
Switch the ohm meter to ohms, R x 1 scale and measure from the LOAD side (non battery side) of the fuse holder to ground, You should not see any resistance, no meter reading. Also step on brake pedal as that's involved in the circuit. That would prove that there is no short in that circuit serviced by the 20 amp fuse. If you do get some resistance reading you should inspect each lamp socket and associated wiring as that's about all that remains in the circuit. Voltage and current are NOT the same thing, but there is a relationship in a DC circuit that is proven by ohms law. You may want to goggle that and read up on Ohm's law. Each incandescent lamp's filament has a certain amount resistance which will define how much current is drawn from a given voltage source. It's all math.
Since you don't know a lot about this car and it's history, It's probably a good idea to separate the bulkhead connector as well as other connectors and check for corrosion on the contacts, signs of heating of wires, especially where the wire is crimped into the bulkhead pins. If you see the green corrosion scum that's not good and needs attention.

 

[1 Wild R/T]

Check to see it all the bulbs are the proper type... Often I've see 1156 bulbs where 1157 bulbs belong... Yes the 1157 has a stepped pin but people get them wrong and still get them to turn...

 

[Mariposa Mike]

Starting work on this today and just want to check if the incorrect bulbs could be causing too much draw. Across the back I found five 1157 bulbs and one 1034. Also found pinched wires on one light but no insulation damage so my aha moment went in the toilet. I will be working on the rest but also noticed this morning the driver side head light would not open. Thought I was buying a running sorted out car and hoping to go to some meets this summer and fall but looks like that ain't happenin'. So if I'm supposed to have 1034 across the back I need to make a trip into town for bulbs after I do the Ohm check.

 

[Mariposa Mike]

Couple more questions. When looking at the front parking/turn lights I do not see a way to get to them. I have a 66 Chrysler Corp manual that came with the car along with a 66 Charger Supplement to that manual but it does not show the parking lights assembly. Also the rear interior lights do not appear to have screws holding them in so I believe it might be a tension fit and they could be pried off. But I don't want to go that until I know for sure. Any help on the issues???

There was a previous link for a 67 manual and possibly that would have more info on these cars. Was the Charger a mid year addition to the Dodge Coronet line? and maybe that is why they are not in the 66 manual?

 

[Fran Blacker]

Need to remove splash shield, bolts could be covered in undercoat. Service manual link you can download. Service Manuals – MyMopar

 

[440 4 speed]

Look carefully at the housing. You will see that the housing is screwed on. Remove the screws, take the housing off. Remove the plastic lens and you will see the bulb.

 

[Mariposa Mike]

I've been off line for a few hours due to my clicking on the Service manual link and somehow getting malware that shut me down. Had to have my wife and an Apple tech bail me out of computer jail. I will go back to the car and look again to see if I can find some screws. In the meantime I went to O'reillys and of course they were out of 1034 bulbs but one of the counter men mentioned that the 1034 and 1157 are the same bulb. I ordered the 1034 in a 10 pack to pick up later but maybe someone could chime in on that one. Are they the same? Maybe superseded for some reason. The only 1034's I had were three old bulbs. Not enough to start over on the back. I looked and removing the splash shield would not have helped BTW.

 

[kiwigtx]

I've been off line for a few hours due to my clicking on the Service manual link and somehow getting malware that shut me down. Had to have my wife and an Apple tech bail me out of computer jail. I will go back to the car and look again to see if I can find some screws. In the meantime I went to O'reillys and of course they were out of 1034 bulbs but one of the counter men mentioned that the 1034 and 1157 are the same bulb. I ordered the 1034 in a 10 pack to pick up later but maybe someone could chime in on that one. Are they the same? Maybe superseded for some reason. The only 1034's I had were three old bulbs. Not enough to start over on the back. I looked and removing the splash shield would not have helped BTW.

Blowing the fuse is typical of a short circuit - check all wiring looms that pass through steel bulkhead or panels. You will find a wire that has chafed through its insulation.....or a terminal has popped off somewhere and is touching the body.

Bulkhead areas and steering column is a good starting point - you might even have a twist in the loom between the steering wheel and the floor - pulling on the wiring can cause an issue.

Less likely is the 'wrong bulb' thing mentioned above. Short circuit equals direct path to ground from a power source.

 

[kiwigtx]

Below is a picture to demonstrate the best short-circuit available ----- direct path from positive to negative on the battery.

 

[Fran Blacker]

I've been off line for a few hours due to my clicking on the Service manual link and somehow getting malware that shut me down. Had to have my wife and an Apple tech bail me out of computer jail. I will go back to the car and look again to see if I can find some screws. In the meantime I went to O'reillys and of course they were out of 1034 bulbs but one of the counter men mentioned that the 1034 and 1157 are the same bulb. I ordered the 1034 in a 10 pack to pick up later but maybe someone could chime in on that one. Are they the same? Maybe superseded for some reason. The only 1034's I had were three old bulbs. Not enough to start over on the back. I looked and removing the splash shield would not have helped BTW.

Sorry about your getting malware. I've never had a problem at that site. In the future I'll mention that.

 

[Mariposa Mike]

The computer tech said it was more than likely I inadvertently clicked on one of the ads/icons that drift around the outer page and in the middle. I will still need a manual but for now while I am trying to address these electric gremlins I will stay off anything that could get me into further trouble. The tech at one point after asking numerous questions said "you aren't a computer person are you". I replied absolutely not!

 

[Billccm]

Get a socket for a 1157 bulb and solder on some clip leads. Clip the bulb across the fuse socket that keeps blowing. Now if the circuit is going to blow the fuse the bulb will glow BRIGHT. Now disconnect items starting at the taillights and move up the harness until the blub stops glowing. Perform the wiggle test as you go while looking at the blub. You may need to jump the brake lamp switch as you troubleshoot down the paths.

Keep in mind tail lamp sockets themselves can short. The coil springs on the bulb contacts can crack/break and intermittently short to ground.

 

[nbbcrh]

A new to me 66 Charger has several electrical issues including the stop and interior lights 20A SFE fuse blowing. Does not happen immediately but after my wife was pressing on the brake pedal with the door open it eventually went kaput. The only other thing she did was press on and release the E brake. That light stays on so no short there. Since there are 6 lightbulbs across the back and 4 more in the interior, is it possible there is too much load on the one fuse? I'm also having other problems with electrical such as no horn and emergency flashers not working. Also the starter is not always working but I have power to the starter relay so it might be the relay. Previous owner replaced the starter with a high torque (smaller) unit and that looks to be recent. I think he might have been chasing some of these issues since I am finding lots of spare fuses, ballast resisters, and such. Oil pressure gauge not working either and he has a spare module for that from MEGA parts. Any idea on what might be happening to the light circuit? Previous owner passed away so no help there.

Mike, I was having the same problem on my 66 coronet, I am in the process of restoring after sitting for years. I kept blowing the same fuse after putting all my wiring harnesses with new bulbs back in. I had a ground somewhere, did the test on moving the wires around while test light was showing ground somewhere.Engine, lights and taillight Harnesses had been cleaned before reinstalled, had good connections. I had restored dash and the wiring harness about 5 years before and covered up in garage. I didn't do anything else to it but reinstalled it. I had headlights but no dash or tail lights. I disconnected and removed light switch, cleaned and reinstalled, everything works and 20 A fuse quit blowing and ground is gone. I really should redo everything in my dash. I guess over the years the cold and hot the garage goes thru has lost good connections. I was lucky it was light switch connections.

 

[Mariposa Mike]

More good info. I have a spare headlight switch that came with the extra parts. Like I mentioned before the PO was obviously going thru these same issues. There is also a funny looking clip on the headlight switch I believe meant to keep it in place or the knob in place. Kinda like a straight slip pin with a tension arm on the other side. Like we see on Chinese products. Just have not looked further into that one but maybe it has something to do with him already changing out the switch. I kinda figure I will be going in there to check the connection coming from the power pack. So as soon as I can get the rest of the bulbs out and check the sockets and check for an open I will be able to run this kind of test if nothing is found. Two of the tail light bulbs I pulled out fell apart in my hand but had been lighting up before.

 

[bm02tj]

I had that on my 73 and it was a wire pinched under rear seat so follow ever circuit it could be any where

 

[Mariposa Mike]

That would be my luck. Could be anywhere...... Good luck sucker. I suppose whenever, if ever, I get these problems fixed it will be a fun car to drive. Have our CHP coming here Thursday morning to do a VIN verification so I can finish registration. I was going to drive it to them until zzzzzst no stop lights.