More Wiring Woes - Couple of validation questions

[FL911SC]

Greetings all,
Finally got the engine back in the car and running. However, when I hooked the battery up, I watched a fuse smoke and then burn out. (It is amazing how long they take to burn through). Now that the engine is going, time to chase the electrical gremlin.

The circuit is the Hazard Lights and fuse #17 blows when the hazards switch is engaged.

I have stared at the wiring diagram and here are my questions so far:

1) Is the power from the battery applied at the from the bottom of the fuse panel? In other words, does the current move from the bottom of the panel to the top, or the other way round?

2) In the attached image of the wiring diagram, there is a symbol marked with an orange arrow, what does this mean? My guess is that it is a wiring connection which can be disconnected, like with a spade terminal but I am not sure. In this example it would be a black/white wire going to a connection with 2 blk/wht wires on the other end.

3) At the top of the diagram, at the read arrow, it shows a black/red wire leaving the fuse panel and going to the switch. In the pictures, you will notes there is one black/red wire at the bottom of the fuse panel and 2 wires at the top. Why are there two wires? The diagram implies should be only one. (Different Left and Right circuits?)

Wiring Diagram for Hazard Light Circuit


FROM BOTTOM OF FUSE PANEL:


FROM TOP OF FUSE PANEL (note two reds wires on Hazard circuit)


Thank you for your help. I hate chasing electrical problems, but it is part of the deal I guess.

Keith P.

[ChrisHoover]

These are hard questions to answer because they are so specific to your car. Sometimes it helps to understand generally how things work then evaluate the specific condition. Circuits are a loop from the battery through a load and back to the battery. By convention we say current flows from B+ to ground. I think electrons actually move the opposite direction. When reading the schematic, you are looking for a complete path from the battery and back. Generally the B- is not completely shown. It is usually indicated by a ground symbol.

To trouble shoot disconnect any conductor connected to the fuse and trace it to its origin. Metering is essential. Checking continuity between the battery and the disconnected conductors will identify the source conductor. The other two are the load.

Checking continuity of each conductor to ground should identify the conductor blowing the fuse. If there is a load between the conductor and ground you’ll see a number in ohms. If you see a very low number like 0 - 4 you probably have a fault.

If you have spare fuses you can connect one conductor at time to the source and see which one blows the fuse. No disrespect but this how older electricians id a breaker or fuse. Place a short on the circuit and see what blows

[timmy2]

Top of fuse panel is unfused input, bottom is fused output for your year.
Factory color schematics for 78/79 here:
https://www.dropbox.com/s/yjfoxfvwlci6lys/911_electrical_78SC_USA.pdf?dl=0

Note: S=Fuse and they are numbered from right to left staring with #1 closest to the headlights.
The skinny black lines between some fuses means they are bridged internally to each other.

[FL911SC]

Thank you Dennis, that is helpful.

Regards,
Keith

[kltarga72]

QUOTE: (I watched a fuse smoke and then burn out. (It is amazing how long they take to burn through)

A slow fuse blow (3-5 seconds) to me would indicate a possible pinched wire to ground, not a dead short to ground. Maybe when reinstalling the engine a wire was pinched in the process? I'm also assuming you did not have this fuse issue prior to removing the engine.

[FL911SC]

Lash, you are correct in that I didn't have to problem before. Full disclosure, the car just just back from paint and interior, it was almost completely disassembled and put back together during the process. I had the motor out working on it in the mean time. I finally got it back in and everything hooked up.
With that said, the possibility of a pinched or shorted wire is very high. I am trying to understand the symbols in the wiring diagram so that when I start checking continuity, with fuses and bulbs out, I will have a better idea of when I should have continuity to ground and when I should not. Hopefully that will lead me to the problem.

[timmy2]

This should help with the symbols and nomenclature:
https://www.dropbox.com/s/ds7l4egzvqa2w18/understanding%20euro%20wiring%20diagrams.pdf?dl=0

[FL911SC]

Thank you again Dennis!!

I have a place start. While unhooking everything I found the two lights on the left side were installed backwards. I haven't had time yet to get under the car, but I am thinking the lighting assemblies might be hooked up wrong, causing the short.
Fingers crossed.

The marker light and the turn signal fixtures are backwards. Does anyone now which direction the "ripples" on the reflector are supposed to face? I am not sure and I don't know if the right side is correct.