Wiring in some gauges and a stereo.

Might be a dumb question but I'm curious. I currently have my instrument cluster pulled out. I am also about halfway through installing a set of electrical aftermarket gauges and a retro sound stereo system.

The guy who owned the car before me apparently tore out a ton of the original wiring and I'm not sure which wires left are hot let alone which ones are only on with the key.

I do know there is a hot and a ground powering the cluster connected to the back of the alternator gauge. Is it a bad idea to hook some additional wires to those terminals to power my gauges and/or stereo?

Thought I'd ask before I burned my car to the ground.

73 Duster 360 said:

I do know there is a hot and a ground powering the cluster connected to the back of the alternator gauge

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Depending on year, The black and red on the back of the alt gauge are both power. One from alt, one from battery.

Your best bet is to get a free (mymopar.com) or buy (classiccarwiring.com) a wiring diagram for your car. Then start tracing.

You might want to think about buying a good used or new OEM style dash harness

Dana67Dart said:

Depending on year, The black and red on the back of the alt gauge are both power. One from alt, one from battery.

Your best bet is to get a free (mymopar.com) or buy (classiccarwiring.com) a wiring diagram for your car. Then start tracing.

You might want to think about buying a good used or new OEM style dash harness

Click to expand...

Both power? Interesting. Good thing I didn't just start hooking things up.

Yes!
Chrysler frequently used black for power feeds. A little less so by '73, but unless you know its a ground, assume its a feed.

On most* 1973 A-bodies the battery and the alternator output are tied together at a welded main splice.
From the main splice power can flow from either power source to various circuits.


See if you can identify these main circuits.
Problems can often occur at the connections, either the contacts, the crimps or sometimes the wire just beyond the crimp.
Column connector feed and both power supply feeds through the bulkhead are the ones that seem to get the most abuse and deterioration.

The label 'alternator' on the ammeter is unfortunate.
The ammeter is in the battery feed/charge line.
When the battery is supplying power, current flows out of the battery and the meter shows discharge (up to 40 amps).
When the alternator is recharging the battery, the ammeter shows charge.
If the battery is supplying power while driving, something is wrong with the alternator or its connections.

back to your project,
If you will only be using the stereo with the engine running, then you may be able to tie in at the fusebox. See if there is an empty spot. Even so, it depends how much power the unit will draw. On the key switched side that power is going to have to flow through the same feed to the key swtich as every other 'accessory' and the engine systems ignition, alternator, choke assist if present, etc.

*Some Dusters had an optional feed wiring arrangement.
If you see the alternator or battery feeds going through a grommet, that's one of those arrangements
example here Dash Power Feed Confusion

73 Duster 360 said:

Both power? Interesting. Good thing I didn't just start hooking things up.

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What he means is that the ammeter is a (basically) a direct short. So they are both connected together by the ammeter. The black wire is the "loads" wire--feeds off to the lights, key, etc, and also the ammeter. The red one feeds out through the bulkhead, through the fuse link, and to the battery. Be careful. None of that is fused. Disconnect the battery when working with all that

I decided to not mess with the stock wiring and fuse box for anything Auxiliary. I Bought a Painless wired Fuse block and mounted it in my Glove box to power my gauges, stereo and EFI if I ever make the move. It included a relay and circuit breaker. Made it far easier and the stock fuse block is limited on space and separate from the stock wiring system.

So it sounds like connecting to either of those wires would be a bad idea.

73 Duster 360 said:

So it sounds like connecting to either of those wires would be a bad idea.

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It depends.
Mopar did it for certain options on some cars, such as clocks, convertible tops, and rear defrost grids. However the last involved a rewire of the alternator feed direct to that stud.
It depends on what the loads are, and whether these items should have the key on run or accessory to operate.
It depends on how its done. The wires need to be routed so they don't get twisted the wrong way or chafe on sharp metal, etc. There will need to be appropriate fuse or circuit breaker since you're tapping off the main. Things like that.

I hooked my stereo up to the original connector under the dash. This connector has red for power and orange for your illumination control.

I connected the yellow memory wire to the cigar lighter.

My amplifiers are connected to the battery with a circuit breaker.

Doing it this way ensures everything is fused and protected.