Help with '71 Radio wiring

[RickWhite]

Hi all, apologies as this may be covered elsewhere, but I was looking for assistance in wiring a US Frankfurt having removed an Alpine cassette deck. The issue I have is that there are many hot wires, so I don't know which to choose. For reference, this is a '71 911T Targa, completion date ~5/71.

The first, perhaps easiest wire to choose is the red one which puts out 12V when the key is turned and fed into the Alphine unit. It has a fuse already inline. You can see it in this hot mess of wires that went into the Alpine unit.



That red wire is actually connected to what looks like a genuine yellow porsche wire, just behind the ashtray. It is grouped with a blue wire, which isn't connected to anything, just capped. Also note the metal cylander attached to the back of the ashtray, with the red wire hanging out. More questions on that later...



The second group of wires looks like legit porsche wires. The yellow & red wire, with a black wire, puts out 12V, but all the time. I connected this to the frankfurt and a ground, and the little red dot on the face glowed. The blue wire puts out 6v, but only when the key is turned.



Another photo - lucky for me, the alpine installer left the old connection and wires to the original Porsche dash-mount speaker..



Given those three choices, which would you choose to attach to the Frankfurt radio? I'm handy enough with wiring that I can cut and splice and add new connectors relatively easily.

The final question is what is this thing attached to the back of the ashtray with a short stretch of red wire dangling from it?



and another photo of the mystery thing...



Thanks for your help. I know the easy answer (just take the power from the old alpine connection), but was hoping to get the correct answer...

[edmayo]

Every wire harness has a factory radio power wire already installed, if there is no radio it is tucked back into the harness sheath. Radio installers don't know this so they scab into a power source somewhere usually with scotch locks. Look for yellow power wire and remove the rest. It powers up when the key is in the 'on' position. I believe the harness with blue, yellow/red and black is for a Webasto heater. The silver cannister is a condenser probably for radio attachment.

[RickWhite]

Every wire harness has a factory radio power wire already installed, if there is no radio it is tucked back into the harness sheath. Radio installers don't know this so they scab into a power source somewhere usually with scotch locks. Look for yellow power wire and remove the rest. It powers up when the key is in the 'on' position. I believe the harness with blue, yellow/red and black is for a Webasto heater. The silver cannister is a condenser probably for radio attachment.

Thanks...the yellow is the one they used for power into the Alpine unit.

On the condenser, that is what I was hoping for, though why would it only have a red/power line out, doesn't it need a ground as well?

Thanks.

[rvdv]

It’s grounded through the metal case, bolted to the chassis.

[RickWhite]

So just to confirm, I should use the yellow wire to get power when the key is in the "on" position, and the condenser gets wired in parallel (same clip) into the Frankfurt, to suppress electrical noise?

[rvdv]

Yes, use the “switched” yellow wire for +12v. I would do the hookup without the condenser, if you have background noise or high frequency whining coming through the speaker then hook up the condenser like you said, in parallel. Normally the condenser is hooked up to the source where the noise is coming from.

[Arne]

FWIW - The factory yellow power lead to the radio in my '72T is not switched, it is hot all the time. This is consistent with other '70s German cars I have owned in the past. Since our cars don't have a true Accessory position on the ignition switch, Germans wired the radios so that they could be switched on regardless of the ignition switch position. I recall re-wiring the radios in both my Mk 1 Sciroccos ('78 and '81) so that I didn't have to manually turn the radio on and off when entering and leaving the car. I will leave the wiring in this car as is, as these days I seldom turn on the radio anyway.

[PMNorris]

Make sure you put a fuse inline on your power cable (I managed to fry my Frankfurt as it does not have an inboard fuse).

[RickWhite]

Make sure you put a fuse inline on your power cable (I managed to fry my Frankfurt as it does not have an inboard fuse).

The power has a 7amp fuse on it, which I think is OK?

Fired up everything and it worked like a charm. Now to hack away the underbrush from the Alpine harness and try to remove the factory speaker without damaging too much. Thanks for your help everyone, I'll post some photos once it is fully installed...just need my bluetooth dongle to clear customs.

[bobmagyar]

I am installing my Frankfurt unit at the moment. I would like to confirm that its ground comes from the brackets that are held by nuts to the switch shafts. If so I will make sure that there is not paint interrupting the conductive path.
I can confirm that there is a conductive path between the brackets and the galvanized outer case.