Electricity... dash/tach/bulkhead questions

[jbaha]

Hi everybody!

I'm in the process of rebuilding the harness, it seems that it has been already  (badly) rebuild in some ways.

The dimmer has fried the black wire from the ammeter was cut and twisted... the bulkhead has also fried.

I was looking for the tachometer wire since it wasn't working... and the grey wire goes to...! the transmission???!!! As i saw on the wiring diagram it's not really normal

Also, the clock wire is pink, and the bulkhead connection are not on the good spot.

Is anyone knows what kind of harness it is? I have a rallye dash (it's a 74 318 ci challenger)

thank you!

[70chall440]

I am not sure what you are asking; I would believe that the harness is for that car. If the car did not come with a Rally dash but then one added (very common occurrence) the original harness would have still worked but they would have had to add a wire for the tach and moved some wires around to align with the new rally cluster. You can usually tell by looking at the light bar above the instrument cluster, a non-rally has 3 light bulbs and a rally has 4.

Unfortunately you are probably going to have to trace every wire and rebuild the harness as you go. I've done this a few times over the years and it can be a pain, but with patience you can get through it. Do not look at it as a whole harness, look as one thing at a time and trace it out. A good diagram is is must but also a note pad so you can make notes as you go. Usually, i have a diagram from a 70 as well as the newer cars available as I have found that there times when the 74 diagram isn't making sense, look at the 70 and then you see how they did it (sometimes this works).

The harness for the 74 should be the same as the 72 and 73 as well, but a 70 will definitely have a few small changes that may or may not apply.

Of course your other option is to purchase a new harness and start clean, not cheap and in your case not fast to get, but you get nice new wires to work with.

[jbaha]

Thank you for your reply. I was just wondering if someone has already  seen this kind of harness (pink to the clock).

Well I think it's the way to go, (identify each wire)since thy are looking good except the ammeter but i'm doing a voltmeter conversion.

Yep, a new harness isn't cheap, and it's just wires and a fuse box, I wish someone did a kind of motogadget m-unit one-wire-thing for old cars!

Will post pics later!

Update : I have the 4 +1 bulb of cluster lights and the seat belt interlock system  it has been by passed in the past.

I've found that the black and white wire from the tach that goes to the coil, means  the tach is gone    .

I identified all the wires at the bulkhead, i've found the brown from the washer switch was "attached" with tape (yes...) to the coil!! I now know why there were some sparks when i was actionning it...

IS it possible to simply remove all the cables and kinda relay from the seat interlock?

[70chall440]

Sounds like you are making some progress.

I don't understand your last question, are you asking if you can disconnect the seat interlock? If so, I am certain you can, unlike more modern cars, the 70's cars merely gave you a warning that your seat belt wasn't on by emitting a beep or noise, we use to find the relay and pull them to stop the noise and then carried on.

[jbaha]

My question was : Is there a possibility to remove all the wires connected to the interlock system as if it had never been here before... 'cause it's a lot of wires and  with the reset relay under the hood (in fact I would really like to clean the engine bay from visible wires).

I'm throwing away the old bulkhead connector, replacing it with this : https://www.te.com/usa-en/product-207305-1.html

[70chall440]

Yes, I believe you can completely remove the interlock an all of its associated components without effect.

So if you are going to replace the bulkhead connector with the one you posted the link for, are you also getting the connectors for the engine compartment?

[jbaha]

Yep, it's the same type (male/female), I'm replacing the contacts with crimp pin 3+. The new connector will be inside the car, wires passing through a grommet. The big gauge wires will be continuous (no connectors).

[70chall440]

Very cool, good luck

[jbaha]

little uptade, I removed completly the interlock system, pretty easy in fact, just follow the wires and reroute some, remove some. Just follow the 70 rallye wiring diagram.

Cut my thumb with the jig saw making a plastic plate for the new bulkhead yesterday (nothing crazy), i'll continue tonight . hope it will start hahaha 

[70chall440]

Good job on the interlock removal, sorry about the cut hand, power tools can be dangerous.. but getting cut and/or injured kind of comes with the territory.

[jbaha]

Hey!

Everything work unless the wipers... I connected a ground wire from the motor strap to the negative nothing happens (still the 1 speed and no parking); connected a ground wire from the switch to ground, here it is! it worked! but now , I just don't know what wire is used for ground ... how to deal with that?

Thanks

[70chall440]

I am not sure what you are asking. Both the switch and the motor are grounded, the motor gets grounded via that brass strap on one corner, the swtich gets grounded through the dash frame which is screwed to the body/sub-frame.

[jbaha]

thanks.

Can't see where the dash frame of theses switches are grounded via the frame, kinda strange when i compare mine with internet pics. I think, i'm just gonna run a new wire from the metal panel to the frame.

I'll post pics off the new installation tomorrow if it interest someone in the future

[70chall440]

Is this a rallye dash? Regardless, three is a metal component of the switch panel that screws into or against the metal dash frame. The switch is screwed into a metal plate, that plate at some point is screwed to the dash which provides the ground. That said, running a wire will not hurt it.

[jbaha]

yes it is a rallye dash. But at the screw location there's just plastic...maybe it was replaced since the dimmer as completly fried.

Here's some pics of the new installation : 

- Wires passing through firewall to a new connector
- Complete removal of the belt interlock system
- Ignition and Start wire without connection (direct feed)
- Voltmeter conversion with the bypass of the bulkhead connector (the big thing on the right of the engine is a maxifuse)