90 Sierra Won't Start

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Gary B. Golden - 07 Jan 2006 23:24 GMT

1990 GMC Sierra won't start. All electrical appears good except nothing
happens when you turn the key . Battery has been checked out (even replaced
with another new battery) but no luck. Idiot lights come on on dash, but
not even a click from the starter. Lights, radio, turn signals, horn all
work. I suspect the neutral switch or ignition switch. Anyone got any
ideas? Or want to suggest a path for troubleshooting?

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Whitelightning - 08 Jan 2006 17:37 GMT

> 1990 GMC Sierra won't start. All electrical appears good except nothing
> happens when you turn the key . Battery has been checked out (even replaced
> with another new battery) but no luck. Idiot lights come on on dash, but
> not even a click from the starter. Lights, radio, turn signals, horn all
> work. I suspect the neutral switch or ignition switch. Anyone got any
> ideas? Or want to suggest a path for troubleshooting?

You gave us the year and model which is a good start, but engine, tranny are
a major help as well.
Put a test light on the small terminal on the starter solenoid and see if it
lights when the key is turned to the start position. If it does, starter.
If it doesn't the next thing to check is the neutral safety switch located
on the top of the steering column just before the column goes through the
firewall, assuming this is an automatic. If its a stick its on the clutch
pedal linkage. Try holding the key in the start position and with your foot
firmly on the brake pedal slowly move the shifter from park to reverse to
neutral to drive if auto. If it engages the starter doing this the switch
needs to be adjusted, the mounting tabs on the switch are slotted. With out
looking at the plug to jar my old memory, I cant tell you which two wires go
to the starter from the ignition switch. get a wiring diagram, or perhaps
someone will jump in and you can "jump" the two wires and see if it starts
then. If it does then it is the switch, or again it could be out of
adjustment, it too uses slotted mounting tabs.

Whitelightning

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Gary B. Golden - 08 Jan 2006 21:04 GMT

Sorry about not giving engine and tranny info. It's a 7.4L with a 3-speed
automatic.

>> 1990 GMC Sierra won't start. All electrical appears good except nothing
>> happens when you turn the key . Battery has been checked out (even
[quoted text clipped - 29 lines]
>
> Whitelightning

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Gary B. Golden - 08 Jan 2006 22:48 GMT

It appears the neutral switch is a plastic housing (that has some adjustment
with plastic tabs. Tried moving it back and forth with the key in the start
position; no luck. There are two connectors on the housing. One connector
has a black/w white stripe and orange/w black stripe wires. The other has a
green and a blue wire. Neither matches the wiring diagram I have (from a
Chiltons GM Full Size truck repair manual 1988-93. The electrical system
wiring diagram shows only a yellow and purple to the neutral switch.

The starter has one of the shields that makes it almost impossible to get to
the solenoid with the truck on the ground.

Holding the key in the start position and slowly moving the shifter from
park to reverse didn't get me anything either. Before I attack the starter
I thought I'd check out the neutral switch. If someone can tell me which
two leads need to be jumped, I'll remove the connect and try that. One
connector comes off easily ( the one with the black/w white stripe and
orange/w black stripe wires ). I haven't figured out how to get the other
one off yet. It isn't apparent where the hold-down tang is and it doesn't
want to come off. It's impossible to see what's holding it in place so I
can only guess there has to be a tang there somewhere.

>> 1990 GMC Sierra won't start. All electrical appears good except nothing
>> happens when you turn the key . Battery has been checked out (even
[quoted text clipped - 29 lines]
>
> Whitelightning

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