99 WEIRD ELECTRICAL START ISSUE

Okay folks I have a weird one.

99 A/T 4x4 Tacoma will not start from key.

However if I use my power probe and apply power to starter directly to pin where relay is it starts.

So here's the weird thing.

The starter wire at the ignition is cut (an ignition interlock/DUI device was previously in there at some point).

I originally thought it was a bad crimp on their spade connectors but nope not that.

This is the weird thing if I unplug the spade connectors on the Black starter wire near the ignition switch and test for voltage these are my readings with the starter wire technically cut.

Ignition switch when cranked to start does put out 12v like normal on that black wire.

BUT what's throwing me for a loop is the other side (heading to relay) has 12 volts present when the key is in the "On" position???? But what's even really weird is the relay still shows ground on the coil pins (I have the relay removed). I get that one pin should show ground and the other should show nothing at rest and 12v when in "start position", but it's showing ground too.

So how the heck do I have ground at the relay, but 12v at the ignition switch when it is literally the same wire according to diagram?

I'll post a pick of the diagram I have with what my readings are to help get a better picture.

I'm almost guessing there's a break in the wire (I don't know how cause the Harness looks fine) and one side is touching ground and the other is touching 12 volts.

Im just thrown off on the fact that there is 12volts on the starter signal wire when its not in the start position, yet theres ground at the relay and nothing changes at the realy when key is turned to crank.

It's like half the back wire sits at 12volts and the other half sits at ground towards the relays side.

Remember the wire is cut and the relay is removed for testing.

Its like something is sending 12 volts the reverse way up the starter signal wire to the ignition switch, when in reality the ignition switch is what send 12volts out to the starter signal wire. Im just so confused on how 12volts is present on the relays signal wire when its in the "ON" position, yet still shows ground at the relay pin (relay is removed). It should only be showing 12 volts when in "Crank" position only, and that relay pin should also show 12v when in crank, but it sits at ground and relay never closes

 

What engine? 3.4?
I want to see the whole diagram.
The ground side of the relay goes to other places too.

I have the diagrams, I just need to know what engine.

 

It's the 3.4

 

The relay is removed so that's why I'm confused on how the heck I have ground on both pins. The 12v side pin is grounded yet at the ignition switch it shows 12v? It's the same dang wire according to all the diagrams I've looked at! So how can a single wire show 12v and ground on different ends unless there's an interrupt somewhere down the line

 

Ok. So let’s be clear.
With the wire DISCONNECTED at the spade, you have power to BOTH sides of the wire with the ignition on?
And this is also while the relay is REMOVED?

 

I don’t think your wiring diagram is correct.
Mine is a bit different.

PM inbound.

 

Yes.
-With spades disconnected and relay disconnected and just key in "ON" postion I have:

Relay shows ground (both pins)
Spade side: Heading out to relay according to diagram shows 11.1 Volts
Spade on ignition switch side: NO (normal since key is not in crank)



-With spades disconnected and relay disconnected and key in "CRANK" postion I have:

Relay shows ground (both pins)
Spade side: Heading out to relay according to diagram shows 11.1 Volts
Spade on ignition switch side: 12 Volts (normal since key is now in crank)

So I'm just lost on how the heck that the one side with the Spade that supposedly goes strait to the relay is showing 11.1 Volts on one end but ground at the other???

 

I guess, I should ask?
What is your problem?
What are you trying to fix?

Are you blowing a fuse?

 

Truck will not start by key only starts by applying 12v on PIN 3 of relay. Key is left in ON position while I use power probe to apply 12v

No fuses blowing.

That's why I'm digging into this, cause truck can only be started at the relay pin or at the starter solenoid. For some reason wire from key to relay is faulty

 

I would imagine the interlock would've required accessory power in order to operate before attempting to crank. Assuming that's correct the black wire with voltage in the on position will be on a different circuit and the wrong wires got reconnected when the device was removed because they were the same color. Easy enough to tell with continuity checks at the fuses.

 

How old is the ignition switch......you might be getting a 12v reading on output on black.....
but then over stressing it when you thro some amps at it........

Bad ignition switches....a lot of times are fine at idle......or at low load.....


As far as seeing 12v coming out of the starter signal wire coming back up from the starter............that ground is shared with the open circuit relay...so pump powers same time as starter......you're probably seeing slight residual current coming from the fuel pump branch.......
Somehow all that has to be inter mixed so the fuel pump operates both in start mode and then run mode......uninterrupted....

 

I like this idea makes perfect sense .

the interlock would act just like another starter safety switch when the interlock is satisfied the circuit closes allowing the truck to crank.

Find the wire coming from ST1 run it to the #1 pin on the starter relay if the schematics are correct that will fix your problem.

I am hoping you bought this truck in this condition or helping out a friend.

 

Helping a friend!

 

I've checked for mis wired connections but those were only t-tapped and the starter is the only thing that gets cut. (I used to install interlocks) I will double check though!

 

That starter circuit has a 7.5 amp fuse of ignition, so I know it's not switch cause I did exactly what another person said and run a wire to the fuse box (temporary) so I can now start it with key but that also means it can be started in gear now.

I think your right about residual voltage.

Can you post the diagram for the open circuit relay?

And if there's any diagrams on the Park/Nuetral position switch (A/T).

I'm gonna tinker with it today and see what I find

 

I can probably help. But it will be later once I get home.

 

You are correct it’s shared with multiple systems.

 

DMs inbound

 

Who knows other starting circuit issues might be effecting things besides the Interlock removal.

For What ever reason the starter relay coil is not being energized.

It can be a pain because 1 strand of wire will ring out but not be able to carry enough current.

Up close and in person.

Good Luck OP

 

Ended up being Neutral Safety Switch! Appreciate the diagrams! Those were a big help! Just jumped the 2 wires temporary to get it to start by key!!!

Thanks all of you especially TNSHOOTER!