Not what I expected!

[Dr.Jass]

Over the weekend, browsing around the 'Bay, I found an interesting item for sale: An NOS factory electric hood latch, apparently for '73-'75 C-bodies. During a call with my GA friend last night, I axed him if he'd ever heard of such a thing. He had not, but was intrigued by it. It looks like your standard hood latch, except there's a solenoid built into it.




While we were on the phone, I searched the part number and lo, there was another NOS one available for less than 1/3 the price. I decided to go for it and hit "Buy it Now" based on the description for the first one: An electric hood release. I thought it might be cool to open the hood latch from a key fob, especially with hood pins. The standard procedure for pins with a dash-mount hood release is: Get out, pull pins, go back to interior, pop hood, etc. It's all a bit silly; my '73 Charger was like that. Kind of a pain, but I like the security of my hood release being behind a locked door.

Tonight after I got home, I decided to do a little further research into this item. I found the part number in the '74 catalog, listed as "Hood latch, Use w/Alarm System". Hmmm... alarm system? I must know more about this, so I got a bigger shovel and kept on digging.

Check this out: In 1973, Chrysler started offering a solid-state electronic alarm system on the C-bodies. It's a pretty involved network involving numerous switches, solenoids, etc. The hood latch is but one part of that system. Others include a special switch for the ignition lock cylinder (apart from the ignition switch itself) and switches that connect to the door lock cylinders. Special dome-light (door) plus hood and trunk "pin" switches get in on the fun, too. On the dash, there's a "panic button" labeled "LOCK ALARM". There's an underhood control module in charge of everything. The module's connection actually takes up an entire bay on the bulkhead connector, along with a few other connections. Getting the $102.50 alarm also mandated electric door locks and an interior hood release.

Here's how it works: When the alarm is armed, it monitors all these dome-light and pin switches, and if anyone forces open a door, the trunk lid (tailgate for wagons), or hood, it sounds the horn and flashes all the cars lights--even the dome light. Pretty standard stuff, but what's clever is that the arming is done with the door lock cylinders, and by no other means. If you lock the car with the knobs, or use the power lock switch, the alarm stays offline. Lock either door with the key, though, and it's activated. "No biggie--just break a window," you say. Nope--it will also lose its mind if someone forces or pops the lock cylinder and turns the ignition switch. The alarm is disarmed by unlocking either door with the key. If you're in the car and feel threatened, pushing the LOCK ALARM button immediately locks everything and the horn/lights go ballistic until you push it again.

It's a pretty cool system for 1973, but the coolest part (to me) is the hood latch.

The hood latch is not an electric hood release at all--that's a two-way locking solenoid rather than a release. When the alarm is activated by locking the door, the module activates the solenoid on the hood latch. That solenoid disengages the cable lever from the latching mechanism. The hood latch will not work until the alarm is disabled. Y'know how a car's door handle feels like it's not connected to anything if the door is locked? This is the same thing: Pull the hood release, and all you're moving is the cable. The lever freewheels and nothing happens. Even if you reach up behind the grille and pull the latch lever manually, the hood still won't open. There is no "secret manual override" that, once you know the trick, allows you to open the hood with the alarm active. Being a two-way solenoid, it doesn't stay powered to lock the hood. It activates with a pulse and powers off, so pulling its plug to cut the power doesn't affect the lock. It deactivates with another pulse, which I expect is of reversed voltage.

So if there's no override, whattya do if the battery dies with the alarm on, and hence the hood locked? Excellent question, Smithers. Here's Chrysler's advice, per the decal installed on cars equipped with the alarm package:




Notice that you have to leave the key in the unlock position when you apply power--unlocking the car with the key with no battery power will not shut down the alarm system. That's pretty techie stuff for the early 1970s.

I really like the idea of a locked hood, particularly on my Challenger. I don't need the whole system. The solenoid will work with a ON-OFF-ON momentary switch and a DPDT relay. I could even just use a voltage-reversing switch from a snow plow, though those are big and not easily hidden.

Picture the scenario: I'm gone on vacation and some POS thief decides to break into my garage and steal some of the $7,000 or so worth of Challenger T/A bits--heads, intake, hood, air cleaner base, etc.--off my car for some quick meth money. Alas, Jass locked down the car prior to leaving so the dirtbag breaks the side window. He pulls the hood release handle on the dash and... nothing. He pulls harder and harder, and eventually breaks something but that hood will not open. He's nervous about time now and nothing's working. He gets under the car and fishes about for the hood latch, but pulling it has no effect. Eventually he panics because someone must've heard his floundering by now so he bails empty-handed. I come home to broken window and cable but an intact engine.

Far-fetched? Perhaps, but it'd also keep disrepectful looky-loos from opening my hood while I'm in the convenience store or deter potential joyriders from attempting to hotwire the car underhood. For the $60 total I dropped, it's worth the added security whether I need it or not. It's not what I wanted but I like what it is even better.

 

[69.5CUDA]

ok..that is cool as all get out, and...i want some more info like the wiring diagram n such

hell id like a "cheep" one for my ramcharger

 

[Dr.Jass]

Here's the diagram from the 1974 parts book. Obviously it's not a schematic but it gives you a pretty good idea of the whole system and how it's integrated.




The schematic takes up several pages in the '74 FSM, since the page showing the module itself has most of the connections ending at plugs, which are continued on different pages. The module was mounted under the hood and connects to everything aft of the windshield through a dedicated bulkhead connection.

I found some of the parts available NOS, but they're not inexpensive. The latch I bought was $46 + shipping & tax, which came to $59.14. The only other one I saw (searching by part number) was $175.00 with free shipping. It was claimed to be NOS but it didn't look it, and the cable bracket was missing. That might not be a big deal since later C-barge hood latches mount differently so one might need to fab their own cable bracket anyhow. I guess I'll find out soon enough myself.

If someone's interested in using the whole system, keep in mind that most of these parts are dedicated alarm bits. The hood and decklid pin switches and brackets are specific parts used only with the alarm system. This is also true of the arming switches at the door lock cylinders and the sensing switch at the ignition lock. The door jamb switches are also semi-unique, as they're shared with models with a "DOOR AJAR" warning lamp (it doesn't use the dome-lamp switches). The module itself, its mounting bracket, the wiring and the relays are also not used anywhere else. There are also additional harnesses required if you've got a wagon with any power at the tailgate, or an Imperial (hideaway headlamps).

We've come a long way in alarm technology in the past 50 years. However, electronically speaking it wouldn't take much to make a small circuit to interface glass-breakage or proximity sensors with such a system. This alarm was available on 2-door models, meaning you've got a couple of open pigtails into which such sensors could be wired to trigger the OE module.

I don't put much stock in alarm systems personally, since most people ignore them anyhow (after muttering to themselves, "Idiot doesn't know how to use a key fob"). It would be a pretty hip retrofit being "all Mopar", but I don't know that I'd pursue it due to the cost of questionable 50-year-old electronics. But the locked-hood thing? As an additional security feature, that really appeals to me.

 

[69.5CUDA]

im with ya on the locked hood bit...thats pretty trick, and cant wait to see yours..and...hope youll open it up so we can see its insides, certainly it could be somewhat copied

with a-bodys you can pop the hood n hotwire em in a split second and drive off..so..to be able to lock the hood so to speak is HUGE...

the real idea i have tho is to tie such a setup into a dissabler as well....if you cant get the hood open and cant bpass to get shit working your not going to stick around to try more ideas...

of course these days i think more cars are simply "towed" or trailered off ....cops dont actively check plates on towed or trailered cars...and pulling a plate and stuffing it on a trailer would raise ZERO suspicions

 

[dodgechargerfan]

That's pretty wild for early 70s

 

[Dr.Jass]

OK, so one thing about the latch about which I was mistaken is that it does not bypass the cable release. It simply locks it so the cable won't move. Still, the parts that accomplish this are all metal and far stouter than a hood cable, so once this thing is locked, it's locked for good. The only plastic bit is the link to the solenoid, which only functions for the split second required to lock/unlock the latch. If that breaks, well, you might be in trouble but nobody else is getting the hood open either.

Unfortunately for the "How can I duplicate this?" crowd, this thing is riveted together. I'm not real keen to cut it open just to see how it works, so don't expect those pictures.




Proctological shots provide very little insight into what makes it tick, but these will blow up huge if you want to see:








It did not take this long for the latch to arrive (though right now, I wouldn't be surprised if it had), I just forgot to get pictures of it and better explain its function. I'm very sure this is not a "drop-in" part for my Challenger or any other model beyond a '73-up C-barge, since the latches in the big cars bolts in "backward" to how they're mounted in A/B/E-bodies. I am sure I can make it work with a bit of custom bracketry.

the real idea i have tho is to tie such a setup into a dissabler as well....if you cant get the hood open and cant bpass to get shit working your not going to stick around to try more ideas...

As far as a "disabler" for points, I don't really know how one would go about that. Via a latching relay or simple toggle switch, you could potentially switch the 12V+ wire feeding the ballast to a ground, so if someone installed a jumper wire to try and run the car all they'd get is sparks, a melted jumper wire and a couple of burned fingers (and you'd likely have a smoked ballast). I actually have the same situation with the Valiant, since the Pertronix simply feeds off the existing V+ wire from the ballast. Worse yet, on the Pertronix III the ballast is bypassed so it'll run with 12V connected and never harm the coil. My solution is a barrel-keyed locking SPST switch feeding the fuel-pump relay. Sure, it'll start and even steer (no column lock), but you'll only get as far as the front float bowl will take you.

Like you said, though, most vehicle thefts these days are done with rollbacks, the odd tow truck or a trailer. Any anti-theft system is really only going to deter joyriders... a professional thief will be gone before the horn honks.

 

[69.5CUDA]

shame its all rivited up, i suspect it works just like any ole door latch for the most part

these days the best thing you can do for anti theft is add a couple GPS devices(lost dog ones work) and bury them , however with the points, pertronix and even msd a kill switch will most likely zap ya eventualy, and imo a relay is a must(been there done that), the fact your running an elec pump makes it a whole mess easier

assuming your not a paranoid nutjob

 

[Dr.Jass]

The issue with points or a Pertronix is that a simple jumper wire from battery (+) to either the 12V+ side of the ballast or the coil itself, and the car will start and drive away with a simple screwdriver to the starter relay, especially on pre-'70 cars with no column lock (which isn't actually that hard to break if you're determined). Since neither setup will be on my Challenger, I'm not really concerned about it. It's more the value of what's under the hood in that case... have you priced a bare 340 Six Pack intake lately? They're the better part of a grand used at the moment, assuming you can find one. The locking hood is more of an investment protection scheme.

Joyriding isn't a big problem here, but I did what I can with the Valiant--the fuel-pump lock switch--just in case. Direct access to the pump relay and/or the switch terminals requires the removal of the ashtray, which won't come out with the radio in place (which is no picnic to remove) so it's not like that's easily bypassed. I'll hate myself if that relay ever dies on the road, by the way. I have an interior hood release setup for that car, so someone will have to get past the locked doors just to open the hood in the first place to hotwire it or steal anything. The car's appearance wouldn't inspire anyone to think there's anything worth stealing under the hood anyhow, so why bother?

 

[69.5CUDA]

another fun one is to re-route the starter trigger wire into the the car to a switch or relay then back out to the OE place, its not something you think to look for, the alfa's and the way they are wired showed me this one and seems like the ultimate no your not hotwireing this old car without crawling under to the starter

biggest issue with our old stuff is the sheer stupid simple ability to pop open the wing windows with a pocket knife