1990 SC Basket Case (Electrical)

HelluvaEngineer

Registered User
I was just given a 90 SC with about 97k miles. It has bad electrical gremlins and I'm asking for advice. Here's the short list of problems:

- Brake booster not getting power, therefore pedal won't go down, therefore key won't turn all the way back. This has the electric hydraulic pump, and I checked the 4 pin connector. It's only getting a fraction of a volt.
- Car sometimes cranks, sometimes does not. A screwdriver across the solenoid fires it right up.
- Tach, interior computer (change oil) panel dead, climate control dead, etc (saw these snap to life for about 3 seconds for no reason)

I'm thinking that step 1 might be to replace the main ground cable and clean any ground to chassis that I can find. There is a lot of corrosion on most of the aluminum under the hood.

Thoughts / suggestions?
 
I would start by replacing the ignition switch....
Out of curiosity, why do you suggest that as a starting point? Isn't it possible to test the switch first before replacing it? Or, are you thinking that combination of problems indicates an ignition switch problem?

Thanks, HE
 
Out of curiosity, why do you suggest that as a starting point? Isn't it possible to test the switch first before replacing it? Or, are you thinking that combination of problems indicates an ignition switch problem?

Thanks, HE

Combination points to the switch.

So, how do you test it?

It was easy on Ruby Jean, my 1991 - the sucker was in two parts :(

RwP
 
anything is removable..Includinhg the lock assymbly if you cant remove key!

The ingnition switch box is plastic and poorly made. Ive seen a few in two peices and they are a cause of strange gremlins

Id pull column cover off..You dont need key out to take it out
 
It is very easy to R&R the ignition switch....

I just replaced one on my 92 and it took less than 30 minutes....

Remove the three screws that hold the steering column cover together along with the other wrap around thingy that the tilt lever goes through.....

The switch is held on the side of the steering column with two torx security screws.....

Use a ¼" wrench to turn the torx bit to remove the two screws....
 
two torx security screws
Oh, think I saw that piece last night - white I believe, just past the cylinder assy, closer to the dash.

Are those the kind with a little peg in the middle of the screw (anti-tamper)? If so, I need to stop by Harbor Freight ASAP.

Thanks everyone for this great advice, by the way!
 
Yes, that's them....:D

One other item you need to be aware of....

There is a pin on the steering column push rod that needs to line up with a slot in the ignition switch.....

When you take the switch off, you will see what I am talking about....
 
Success! I pulled that ignition switch box and it fell apart in my hands. All of the pieces were solid, though. So, I put everything in place and peened the metal tabs back over with a hammer, reinstalled, and everything in the interior came back to life. Wow, what a horrible design on that thing.

The brake pump is now getting 14(!) volts, and I can feel a little bit of life in the brakes but the pedal won't go much further down. I think the next step is to check the pressure switch on the booster?

Q: Any reason to replace that ignition switch? Is there a better design now available?

Thanks, HE

Pic:
 

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Oh, another thing - saw the tach barely twitch for a second but it's still dead.

My tach doesnt work either, but when I replaced my ignition switch it came to life for 3 start-up. It hasn't worked since. Could this be a defective part?

Kyle
 
I wouldn't reuse the old ignition switch....

It is an inexpensive part that controls a myriad of functions....

I have not seen a tach go bad, yet.....

I would think that a no tach situation would be related to the DIS module or the cam sensor.....
 
It has lasted 21 years and it's an electrical item. As an engineer what is the probability of failure and life expectancy? (Don’t need an answer just trying to get some thinking started)
Apparently 100%. Duly noted. But it looks like the only issue was that the metal tabs had come lose. I'm wondering if there's a way to rivet that dang thing shut although the probability of me driving this car in 10 years is nearly 0. Either way I'll cough up the $11 for the new switch.
 
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Rivets could work as long as you can get the gun in there.

Sorry, I work with engineers everyday, so I have fun with them. ;):D
 
Rivets could work as long as you can get the gun in there.

Sorry, I work with engineers everyday, so I have fun with them. ;):D
Yeah, I know. We're the guys who design things that can't be machined.

Regarding the brakes, buddy with a Mercury mentioned a good bleed job first. Start with this or tests on the pressure switch?
 
Turn your ignition switch to run, but do not start.....

Listen for the ABS pump motor running....

After about 30 seconds, you should hear the motor bog down as it builds pressure in the accumulator...

Then, if you hear a click and the pump shuts off, your pressure switch is operating correctly....
 
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