Transmission Safety Switch - Explain?

[Seangie]

So before I go and drop half a grand on a new starter...I want to make absolutely sure that there is no way the transmission safety switch is my problem.

Can someone give me a detailed explaination of the intracacies of this switch?  Where can I find it, how it works, and will jumping the starter straight from the battery bypass it?

I cannot see anything between the starter and batteries that would be affected by this switch.

Thanks.

-Sean

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

[Scott Crosby]

On my gm it's in the shift tower.   I have a momentary bypass switch on mine so I can start in gear.  If its in gear the starter won't click or anything.  Fwiw on the gm nothing happens at all when the switch is tripped and you try to start it. 

[Scott Crosby]

Also make sure the rear run switch isn't off.  Same symptom

[sparkplug188]

If you are attaching jumper cables to the starter to test it, you are bypassing all of the safety switches and the entire starting circuit. Either you have a locked up starter or a locked up engine.

We are also assuming your batteries are fully charged and outputting their rated CCA.  It may be worth taking your batteries with you to the auto parts store when you go to look at starters.  They will be able to load test your batteries.  When batteries go bad, they can show 13+ volts, but only output 50% of their rated CCA.  This is especially true in a battery bank.  The good batteries in the bank will constantly try to charge the bad battery.

It would be a real bummer to spend half a grand on a starter when all you really needed was one battery.

This is the starter test procedure from my Eagle manual:

[eagle19952]

Sparks advice would work if you had a fully equipt shop....

In the other thread tom said to tear apart the starter and test it...
You can test it where it is....

The one loud clack tells me the starter is sitting on a dead spot, that the solid clack indicates the solenoid is doing it's job, slamming the bendix in to the flywheel. The only other thing that the solenoid does is deliver voltage to the starter motor.
If after taking the solenoid apart and the contactors are not arc'd that leaves only the starter motor.
The only way to prove the starter bad is to jumper it directly as Tom pointed out in the other thread. I can assure you that IF the starter is good, securing it without a huge vice, it's torque could easily knock over a medium sized child or worse.
It is equally easy (and preferred by me) to do the same test while it is bolted to the motor.

IF you get the clack, when you push the starter button on the dash,and IF your wiring is not butchered (remains [reasonably]stock/OEM) AND you get voltage at the solenoid on the small wire that activates/engages the solenoid/bendix then the wire path thru the neutral safety switch is proven.
The Nsafety sw. is a simple spring pall detent NC (IN NEUTRAL ONLY it OPENS in any other gear selected detent/position) ) switch where wire #100, coming from the starter relay( that would be the one in the back panel with the capacitor on it)  goes to the Nsafety sw, thru the safety switch and then to the starter solenoid. it is located on the transmission on the starter side of your bus.
Again if you get the clack from the dash start button, the neutral sw is good.
PS  wire #44 is the one that is from the starter button , then thru the toggle switch that disables front start. (next to the sw that turns on the engine bay light) thru that sw to the starter relay, whose out put goes to landing spade # 100 in the rear panel, to the neutral sw. then to the starter solenoid key terminal.
There are three groups of spade junctions in the rear panel.
The middle one is where #44 and #100 reside.
#44 is the first spade junction on the left of the center terminal strip and #100 is the 4th one over from the right.

[eagle19952]

additionally, when you locate the Nsafety Sw. and you were to jumper it AND then try to start the engine AND it starts/cranks THHEN that would also indicate the Nsafety sw. was bad.
Provided that the shifter cable is properly adjusted and the linkage allows the transmission to be precisely in the neutral position.
You did say that previously you might jiggle the shifter...that MAY indicate a not properly adjusted linkage.
Note: when jumpering the Nsafety sw. be darn certain that you ARE in neutral, park brake set and lunch box squarely placed under drive wheel...before attempting to start the motor.   

You need two small/medium pair of vice grips any way, you can never own too many...

[eagle19952]

[Seangie]

Hey guys -  Thanks for this information.   I figured it out this morning that it couldn't be the neutral safety switch.  It was late (after midnight) when I posted and it was a long...long day

New starter is in and we are rolling again.


Thanks again for everything ...you guys are awesome.

-Sean