Electrical short 73T, help please....

[kilodawg]

Hi, Just FYI I also posted this on Pelican.

Okay, not sure what happened here and looking for some advice on what to about it if anything.

The other day I finally got around to connecting the Blaupunkt Frankkfurt I got for my 73. There was a rats nest of old wires up under the dash. Some were from the old stereo connection (speaker wires, ground and power) others were vestiges of stereos and and AC long gone. Anyway, I removed as many of the old wires as prudent being sure not to remove any ones that were connected on both ends or needed for the new radio. This resulted in some disruption of the wiring at the lower center part of the dash.

Everything hooked up fine and the radio works properly. It is connected directly to the battery so I can turn it on without a key. Then (here's the big then) I tucked everything up under the dash and secured it with tie wraps. This afternoon, I went to start the car and there was a poof and smoke coming from under the dash as soon as I got to the accessory position on the key. I immediately turned off the car. I turned the radio on and it still works. I then got brave and tried turning the key again. This time no smoke and the car started and at least the lights and gauges seemed to all work.

So what to do now? Leave it alone or start taking the wiring I secured apart and see what might have happened. The only area I messed with in securing wires was at the very bottom of the dash above and behind the radio and ash tray area.

That was also the approximate site of the smoke...

Thanks

[911pcars]

"This afternoon, I went to start the car and there was a poof and smoke coming from under the dash as soon as I got to the accessory position on the key."

If you don't address this, the car could leak smoke again while you're driving or potentially melt the entire car if an extinguisher isn't conveniently available.

I'd first take a peek in the fuse box and see if any fuses are open. If so, that would help indicate the circuit that attempted to fry. There may be a shorted circuit created by a PO that isn't fuse-protected. Look under the dash and search for telltale signs of cooked wires (brown coloration). Non-factory wires usually stand out, usually by them wrapped around existing harness and chassis brackets like a constrictor snake climbing a tree. Non-DIN color on the insulation is also an indication of alien (non-German) wiring.

If the fuses are intact, I bet you could release more smoke by wiggling the wire harness under the dash.

Until you can successfully diagnose the source of the rampant electrons, you might want to invest in a battery-mounted cutoff switch (about $3).

Sherwood

[kilodawg]

Okay I believe I tracked down the source of the problem, I'm just not sure what to do about it. The wire that was shorted must have been an ignition wire from the previous radio configuration. It was not connected and when I tucked the wires under the dash it got shorted to chassis.

So, the Frankfurt has just one power lead coming from it. I wired that to the 12 volt battery lead (again from the previous radio setup). This of course means the radio plays whenever it's turned on. I assumed I had only two options by using either of the 12 volt leads depending on how I wanted the radio to work. Does this sound correct? and if so what do I do to secure the other wire? Just tape it with electrical tape???

Lastly, while I'm at it, there was no ground wire coming from the radio and I'm not sure where one would go. There are one or two places on the back of the radio where I could add one but they would just be going to the chassis. Since the radio is held by a metal bracket that mount directly to the car body does that suffice for a ground?

[911pcars]

Okay I believe I tracked down the source of the problem, I'm just not sure what to do about it. The wire that was shorted must have been an ignition wire from the previous radio configuration. It was not connected and when I tucked the wires under the dash it got shorted to chassis.

So, the Frankfurt has just one power lead coming from it. I wired that to the 12 volt battery lead (again from the previous radio setup). This of course means the radio plays whenever it's turned on. I assumed I had only two options by using either of the 12 volt leads depending on how I wanted the radio to work. Does this sound correct? and if so what do I do to secure the other wire? Just tape it with electrical tape???

Lastly, while I'm at it, there was no ground wire coming from the radio and I'm not sure where one would go. There are one or two places on the back of the radio where I could add one but they would just be going to the chassis. Since the radio is held by a metal bracket that mount directly to the car body does that suffice for a ground?

Verify the source wire for the radio is fuse-protected. Is it a factory wire or an add-on? If the wire leads to the switch, it's probably not protected by a fuse. If so, route a source wire to the fuse box. Most circuits are activated by the ign. switch, but some are unswitched circuits. Check the wiring diagram or test each fuse position with a voltmeter to confirm.

The metal mounting strap on the radio probably suffices for a ground circuit. However, a separate ground wire would be good assurance the electrons have a low resistance path back to the battery. Make sure the connection between radio chassis and vehicle chassis is clean.

Sherwood

[edmayo]

There is always a radio power wire factory wired. It is a yellow wire that comes from the ignition switch that will only be powered with the ignition on. If no radio had ever been installed it would be tucked back into its plastic sleeve in the vicinity of the steering column. Proper installation called for it to routed to the radio along the lower edge of the dash, an inline fuse holder was to be installed near the radio. Whoever installed the previous radio likely didn't know about this and ran some power wire from who knows where, unprotected. Do what Sherwood suggests, unravel all that mess and solve this before you really do some damage.

[Tom F.]

There can also be some unused power leads in that area for the auxiiary heater or air conditioner. You should lay hands on a color wiring diagram, which can help you to locate these.

[kilodawg]

Thanks guys,

In my research I learned why we now have two hot leads that go to radios one straight to the battery and the other thru the ignition. This is probably common knowledge to most but I had this duh! moment last night.

The battery direct line is for the memory functions of todays modern electronics (like internal clock, station presets etc.). So I wound up wiring the radio to the ignition line that smoked last night (it was indeed a yellow wire) where it touched the chassis and secured and taped the battery direct line very carefully. I also installed a seperate ground wire.

That should be about it for this thread