small electrical fire, help with wiring

[cfdlighthouse]

friday night i turned on my headlights, the dash lights and running lights flickered then went off, then a smell of burning plastic smoke. i cut the truck off pulled over and the 15amp fuse for the tailight circuit was melted to the fuse block. pulled what was left of the fuse that melted out and the wire red with yellow strip and one blue dot every 3 inches ourt of the fuse block and drove home.

when turned headlight switch back on i have head lights, brake and reverse lights and turn signals just no dash lights or running lights.

I pulled the instrument cluster and fuse block to investigate for what i would think was a wire or switch that had gone to ground. finding nothing i inserted an inline 15 amp fuse between a power source and the red/yellow one blue dot wire from the tail light circuit turned on the headlight switch and the fuse blew instantly.

checked all the wirining harnesses for damage to wires and nothing.

the wrining diagram sucks

has anyone had this happen before? could the headlight switch be the issue?

any thoughts would be much appreciated

 

[WES1977]

my 40 fuse block did that. but it ended up being high resistance on the fuse box. Sounds like you need a multimeter to mearsure your resistance to ground on both sides of the fuse holder.

To fix mine I just bought a cheap fuse holder for my headlights and my other box is still there but the headlight wires were clipped.

 

[cfdlighthouse]

i thought of that and bypassed the fuse block with an inline fuse and still blew the fuse.

may be im confused but based on the fuse blowing when i turn the switch on that would indicate that the problem is either in the switch or somewhere beyond the switch.

because power is on coming into the fuse throught the fuse and from the fuse to the switch. the overload, resistance or grounding occurs once the headlight switch is turned on.

????

 

[WES1977]

i thought of that and bypassed the fuse block with an inline fuse and still blew the fuse.

may be im confused but based on the fuse blowing when i turn the switch on that would indicate that the problem is either in the switch or somewhere beyond the switch.

because power is on coming into the fuse throught the fuse and from the fuse to the switch. the overload, resistance or grounding occurs once the headlight switch is turned on.

????

I would agree, but using the multimeter would save on how many fuses you blow.

 

[NocalFJ60]

He is right would use a multimeter now if you have one. I doubt it is the headlight switch. Pull all the light bulbs on that circuit and then try another fuse if you don't have a meter. Might have a bad light bulb now.

 

[cfdlighthouse]

i have a cheap multimeter, so i will try looking for the bulbs. i hope its that simple....thanks

just for my information, how do you use a multimeter to check resistance in this case to pinpoint the short?

 

[Pin_Head]

If the fuse only blows with the switch on, then the short is at or downstream from the switch. This circuit supplies the dash lights and running lights in addition to the tail light, so there is a lot of wire in a lot of places. There is no easy way to check it with an ohm meter without disconnecting all of the branch wires and testing them one by one. It may be easier to just follow the wires manually and look at places where the wire or harness passes through the fire wall, sheet metal or rubs up against metal.

The schematic diagram is actually very good. It indicates that there are 12 lights on this circuit (13 if you have the optional glove box light), which is a bunch of potential problems. The good news is that they all have a red wire with green stripe.

 

[WES1977]

Set the meter to the ohms selection. If you don't know what it looks like it's easy to google.
Then place the leads together and see what the reading is. Somewhere around .1 is what you should have. So now put any lead to a good ground on your cruiser and the other to the switch side of the fuse holder. You might get something like .7 ohms and that would indicate you have a short to ground. Make sure it's not M ohms which is ok. Like Pin_head said it's not going to be easy and start unpluging stuff in that circuit and keep checking your meter.

 

[cfdlighthouse]

If the fuse only blows with the switch on, then the short is at or downstream from the switch. This circuit supplies the dash lights and running lights in addition to the tail light, so there is a lot of wire in a lot of places. There is no easy way to check it with an ohm meter without disconnecting all of the branch wires and testing them one by one. It may be easier to just follow the wires manually and look at places where the wire or harness passes through the fire wall, sheet metal or rubs up against metal.

The schematic diagram is actually very good. It indicates that there are 12 lights on this circuit (13 if you have the optional glove box light), which is a bunch of potential problems. The good news is that they all have a red wire with green stripe.

Does you have a copy of the wiring diagram??? thanks

Set the meter to the ohms selection. If you don't know what it looks like it's easy to google.
Then place the leads together and see what the reading is. Somewhere around .1 is what you should have. So now put any lead to a good ground on your cruiser and the other to the switch side of the fuse holder. You might get something like .7 ohms and that would indicate you have a short to ground. Make sure it's not M ohms which is ok. Like Pin_head said it's not going to be easy and start unpluging stuff in that circuit and keep checking your meter.

Thanks for the ohm 101, as far as the job I figured you were going to say that

Thanks