1971 Alarm Problem
 

Hi All,

I am trying to fix the Alarm on my 71 350/270hp M20 car which doesn't toot or make any noise when armed, and any door, or the hood is opened.

https://cimg6.ibsrv.net/gimg/www.cor...108b71fc61.jpg


I have been using the above wiring diagram to work my way through the system. I think I have confirmed that my problem is that the orange wire has no power. But I do not know where that orange wire goes so that I can trace it by hand. Where does that wire go? How do I trace it?

Below are all of the tests that I have done to confirm that my problem is in fact power:

1. Ran a test light from the battery ground to the orange wire, it didn't light.
2. Checked all fuses in the fuse block all good

Here is everything I did to check the ground side of the system:

1. Confirmed black wire attached and grounded to wiper motor
2. Confirmed black wire in relay is solid constant ground
3. Tested each door switch, made sure that all 3 wires were connected and had continuity with each other when the switch was on
4. Replaced the relay
5. Disconnected the flasher, and directly grounded the yellow wire from the battery with the system armed and a door open.

The orange alarm wire plugs into fuse box in the one labeled BAT and should have a piggy back connector coming off your alarm wire for another connection. :thumbs:https://cimg7.ibsrv.net/gimg/www.cor...a067865ddd.jpg

Here is my fuse box, I don't see any dangling wires. The only orange wire from the harness is the brake light I think (pictured here)

https://cimg8.ibsrv.net/gimg/www.cor...3bfd8a888f.jpg
https://cimg9.ibsrv.net/gimg/www.cor...016dcd929e.jpg

A photo of the fuse box with the alarm working would be helpful.

I assume you still have the key switch in the rear taillight panel???

IF SO...then the ORANGE wire is running up the drivers side of the car....and UNDER your door sill plate....and BEHIND your LEFT KICK PLATE and would come out at or by your fuse panel.

IF you get it working again I would advise you NOT to use it UNLESS you are by the car when it is armed. The reason is that this alarm system does nothing more than make noise and can go off rather easily if any of the contact switches fail...especially the under hood one....and it will drain your battery if you do not turn it off.

DUB

I'm doing this because I like things working, not because I'm going to use it, I know it's not really a theft deterrent.

Dub, does my fuse panel look correct? My sill plate screws are frozen in place so going hunting behind the kick panel is going to be a real job.

https://cimg3.ibsrv.net/gimg/www.cor...f1c50323e3.jpg
Not a 71 but this is where my 69 goes

Awesome! I just need to find that connector. Can you photo where that comes out from the harness? I unfroze my sill plate and got my kick panel off!! We're getting close now!

Just a question - have you checked the horn to see if it's good. It's behind the left rear wheel on the back of the wheel well …

Sorry, not to hi-jack, but can anyone ID the tan wire that is plugged in the terminal on the fuse panel? Mine has been spliced, but it runs into the harness next to a purple wire. I don't have a diagram yet to trace it. Thanks!

The Tan (light brown)wire is for the electric windows .:thumbs:

No I haven't

I am first doing this because I don't want to take down my exhaust and unbolt that horn that appears to have been there for 48 years unless I have to.

Can I see a photo of your fuse block, because 69 and 70 cars have a different wiring for the alarm then 71 and 72.

Thanks!

Due to your wiring schematic shows a SPLICE. I would look at the rear body wring harness connector that comes out from behind your left kick panel and you will see an ORANGE wire in that connector

I would ohm that ORANGE wire to the orange wire at your switch at the back oft the car and see if it ohms out. And if it does...then GM is using CLK LTR CTSY circuit to power up your alarm system.....which is no different than how they have it in the earlier years due to that BAT terminal in the fuse panel that the ORAGE wire is being plugged into is being protected by the CLK LTR CTSY fuse.

Or you can pull out the FUSE for your CLK LTR CTSY and ohm out the fuse terminal on the far left and see if it ohms out to the orange wire at your switch in the taillight panel.

DUB

I finally found and fixed the problem -- my horn toots nice and loud now.

DUB -- I did what you said and checked for power at the orange wire on that connector and it was there. I re-checked for power again at the key switch and saw I had it now (maybe this time I was able to probe it better, the probe I am using is a test light with 2 foot of welding rod soldered on so that I can reach the damn thing) and my next instinct was to jiggle the key because now I knew I had power and ground, and when I did the alarm finally went off. I have to put my key at like 2:30 for the alarm to work, 3:00 and it doesn't make good contact. I'm thinking that I'll spray some contact cleaner into the key cylinder and maybe that will clean it up.

Thanks again to everyone for their help. I really appreciate it!

Spraying the contact cleaner will only get to the tumblers and not to the switch portion at the very back of the lock cylinder....which I believe is independent of the tumbler area of the switch. If you are wanting it to work you may be forced to buy a new switch.

I do know the electrical portion of this switch is staked onto the very end of the lock cylinder housing and I have never wasted my time trying to figure out how to get in there and mess a round and fix it when I can buy a new switch.

Still worth a try I guess.

DUB

I have a switch -- I'm just afraid of messing up the body because if there is one thing I know its that I am NOT A BODY guy. Plus I am not sure if this is a good switch or not, it appears to me that the one on my car has two ears that the wires attach to, and clearly this one doesn't.

Here is a photo of the spare switch I have -- can you point out to me what is the actual mechanism? Maybe then I can make some contraption to lubricate the switch from underneath.

https://cimg1.ibsrv.net/gimg/www.cor...b2cd25887a.jpg

If it's a March or later 71, or 72 you may want to rebuild the switch.

My 71 is a mid March, so it's the same as the 72. $$$. The early 71 switch is $30.

I rebuilt my switch....

It is a December of 70 car. What is this switch? Does it mount to that lock cylinder? Can you link me to it?

The switch is a rotary switch with 2 phenolic plates. The outer plate holds the terminals and the inner plate has a brass contact that turns, under that plate is a small spring to push against the rotating plate.

Very Typical of the switch construction in the day. When the switch turned to the on position the brass bar contacted both dimples on the terminals .

I may still have pictures.

Ricks Corvette has the switch, the early one. Part # SWT229

The difference is that where you put the key - the early switch has a nose or dimple , the later look just like the door lock.

https://cimg7.ibsrv.net/gimg/www.cor...e02c340629.jpg
pre -70 alarm
https://cimg9.ibsrv.net/gimg/www.cor...091016547e.jpg
71 late -72
https://cimg5.ibsrv.net/gimg/www.cor...79a4607f99.jpg
71 late -72