'94 100 autobox - no starter

[Mark R]

Cody,
Premise:
A relay buzzes because not enough current is available to "latch" it
(keep the coil energized, even in a non-latching relay).  This can be caused
by a bad relay (high resistance, broken coil, etc.), or what I suspect in
this case- not enough current.

The fact that if you apply +12V to the relay output (starter), the car
starts.  If you jumper (what the function of the relay does) the relay
socket, nothing happens (i.e. not enough curent can flow to the starter
side).  This presumes you're jumpering the right terminals and are using a
sufficeiently large diameter of wire.  Based on your testing, I'd highly
suspect the wiring to the relay (i.e. the new key switch and it's related
wiring).  Sometimes just getting the right voltage during testing leads to
chasing your own tail.  Time to test current flow pre-switch, post switch,
and at relay socket.  That's MY BTDT.   =)

Also, some logic probes don't isolate each side when they're used to jumper
a connection.  That would tend to back up my premise of what's wrong.  The
+12V side sinks towords -12V (0V ground) when jumpered because the current
can't keep the voltage at +12V.  Hopefully my poor description makes
sense.   =)

Good luck with the (maybe) new job,
Mark Rosenkrantz

On 7/5/06, John Cody Forbes <cody at 5000tq.com> wrote:
>
> I was just wondering if theres any BTDTs with a '94 100 automatic who's
> starter won't engage. I'm working on one that has just had its ignition
> switch replaced (by someone else), and since then or thereabouts the starter
> won't engage. I checked all of the wiring at the switch, and everything
> there functions as it should. I traced down to the interlock relay (position
> #4 in the aux relay panel under the drivers side dashboard) and found the
> relay to be buzzing when key is in "start" position. Visual inspection of
> the relay innards looks like its not obviously damaged. I am getting the
> start signal at the proper pin on the relay panel side, and if I put +12v to
> the terminal on the relay panel that leads to the starter the car starts. My
> judgement says the relay is bad, and I ordered a replacement but need to
> wait until Thursday.
>
> The only hang-up I have is if I jump the terminal thats inputing the start
> signal to the relay to the "output" pin which engages the starter othing
> happens. When I do this the "input" is +12v only when key is in start
> position, but when I jump it to the "output" pin it changes to a ground (I'm
> using a logic probe for testing all of this). I suppose that could be some
> kind of strange function, but it worries me that I'm barking up the wrong
> tree.