Re: 1970 99e possible ignition switch failure/short - Saab Saab Model 99 Bulletin Board - Saabnet.com


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Re: 1970 99e possible ignition switch failure/short
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Posted by Gary Stottler [Email] (#1463) [Profile/Gallery] (more from Gary Stottler) on Sun, 23 Sep 2012 07:32:54 Share Post by Email
In Reply to: 1970 99e possible ignition switch failure/short, Duncan Atwood, Thu, 20 Sep 2012 21:01:16
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Duncan,

I would say that generally you would not get a "short" per se inside the ignition switch, but there are several basic things to check. First, do you have a wiring diagram for your car? It will be very helpful - if you need one, contact me off-line and I can scan the one in the Service Manual and send it to you. Here are some other items:

1) Battery Cable (Large red cable from positive battery terminal to starter) - remove both ends, clean everything, reinstall, make sure everything is tight.

2) Negative Battery cable (braided flat cable), ditto remove both ends, clean, tighten. May also have an intermediate point on the body where the negative cable joins other ground wires from the wiring harness - make sure all those connections are clean and tight.

3) There are two large grey wires which connect to the positive battery cable, most likely at the point where the battery cable connects to the starter. One goes to the alternator and one goes to the fuse panel. The latter one is key - it is how battery voltage gets to the whole vehicle. Again, both ends of both grey wires need to be clean and tight.

4) Battery voltage (not fused, so be careful!) goes from the fuse panel to terminal #30 on the ignition switch via another grey wire.

So, make sure that all that stuff is in good condition and delivering voltage to the ignition switch. An important caveat (and common Saab problem) is that as wiring terminals get old and start to corrode and go through heat cycles, they start to loosen and for various reasons build up high resistance. So, if there is no load (open circuit) you may have a reasonable (eg: 12V) voltage reading, but the voltage may drop when you try to have current flow (such as when you turn something on). So, you will want to pull off terminals, make sure they are clean, and make sure they are tight when you put them back on.

It is also common for the ignition switch to get crud in it over time and then as you turn the switch the electrical contacts don't close or have high resistance so things don't come on. The other possible trouble source here is the ignition relay which turns on all the other stuff in the car in response to getting voltage from the ignition switch (brown and white wire from ign switch terminal 54 - or 34, hard to read the diagram). However, that should not prevent the car from running (I am assuming this is a carbureted car).

The ignition switch in crank position should send 12V to the start solenoid from terminal #50 through the yellow wire, and in the run position it should send 12V to the ignition coil from terminal #15 through the green and white wire.

So, if all the other stuff checks out OK, then go ahead and replace the switch (may want to clean the replacement switch with terminal/contact cleaner - Radio Shack - and lubricate the key part with graphite and the mechanical part with white grease.

Good luck!

Gary


posted by 50.48.9...

_______________________________________ Gary Stottler


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