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Amedee, Former ASE Master Tech
Category: Car
Satisfied Customers: 26441
Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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1989 mazda b1600: wont start it will run..injectors..harness

Customer Question

i have a 1989 mazda b2600I 4x4 and it wont start it will run with starter fluid but im not getting power to my fuel pump or injectors. its got a new fuel pump and a reman computer and i checked the wires and all look good and i checked the resistance in the wires from the computer to the injector harness 2 were bad so i replaced them still same problem
Submitted: 7 years ago.
Category: Car
Expert:  Jan Andersson replied 7 years ago.



These trucks have a fuel pump cut-off switch in the cabin, also called an Inertia Switch. It cuts the power to the fuel pump in a crash, rollover etc. to prevent fire. They sometimes trip easily, killing the fuel pump power. It should be in the passenger side footwell area by the firewall. A small black box about the size of a pack of cigarettes. There is a push-button at the top of the box, sitting in a recessed hole. Sometimes the button itself is red. You can push it back IN with a pencil or maybe your pinky finger.

You may have to pull back the carpeting a little bit, but not anything that is permanently glued to anything. Look in the area where the passenger's left foot would go, if he straightened his leg out while sitting on the passenger seat.


That's the first thing I would check.


Customer: replied 7 years ago.
this truck does not have an inertia switch that was what my first thought was but looked and looked and looked and could not find one anywere
Expert:  Jan Andersson replied 7 years ago.

That's strange... I could have sworn I have reset one in a B2600 of that same year or very close. You may be right though, if you can't find it.

It's not that obvious, not labeled or made visible in any way. It was close to where the floorboard started curving upwards into the firewall. What I said about the passenger's foot being close to the switch, is where I found it behind some carpeting, and I have heard of stories of drunken / careless passengers accidentally kicking the switch area, killing the pump :)


I don't have any other ideas at the moment, so I will Opt Out and let other experts here chime in if someone can think of other things to check.



Expert:  Amedee replied 7 years ago.



New expert here!


Have we checked the main relay? THis powers up the injectors and the computer. If the computer is not awake, the fuel pump will not be activated. Or maybe vise versa. The computer may engage this relay by grounding it. Either way, the main relay must engage in order to send power to the fuel injectors. Check the main relay and its function and let me know!


If the main relay is not working, lets check power going into this relay with the key on. There should be two powers. If no power to the main relay, lets check the fuses and ignition switch. If we have power to the main relay and it is engaging, lets check the power wire from the main relay to the fuel injectors.


Here is a wiring diagram.



Edited by AMEDEE on 11/13/2009 at 12:02 AM EST
Customer: replied 7 years ago.
well i have checked the ignition switch with a test light cuz i thought that could be it and the way i understand it that some should light up getting power with the key on the rest should light up cranking it and i have to wires that wont light up with either one is just all black so im assuming it is just a ground one is red with black not the greatest at understanding the wiring diagrams and im not sure were the main realay woudl even be.....with know that about the ignition switch could that be the problem it is bad?
Expert:  Amedee replied 7 years ago.

It is possible!



Expert:  Amedee replied 7 years ago.

Here is a picture of the main relay location. I would recommend we start here and test to see if we have power to it with the key on. Right side of engine compartment.




Edited by AMEDEE on 11/13/2009 at 12:29 AM EST
Customer: replied 7 years ago.
to me it looks like it is on the passenger fire wall, does it have 4 fueses in it if so i already checked all that and theres power to and from that
Expert:  Amedee replied 7 years ago.
YEs.. it is on the passenger side fire wall. It is going to be number 8 in the picture. However, this is going to be a relay, not a fuse. It will be a little black box with 4 or 5 wires going to it.
Customer: replied 7 years ago.
there is 4 wires to the relay 2 of them have power like you said then i plugged in back in turned the key back on and i have power to 3 of the 4 will the fourth light up when it is cranked or should all 4 light up?
Expert:  Amedee replied 7 years ago.
No... there needs to be one ground wire that activates this relay. I believe it comes from the computer. DOes this relay click when you turn the key on or when trying to start the car?
Customer: replied 7 years ago.
yes sir it does
Expert:  Amedee replied 7 years ago.

Ok... good!


Is there a black wire with yellow stripe coming out of the relay?

Customer: replied 7 years ago.
yes sir ther is also a dark green a light green and a blue
Expert:  Amedee replied 7 years ago.
Ok... DOes the black wire with yellow stripe have FULL battery voltage on it when cranking the engine over?
Customer: replied 7 years ago.
it has no volts when i crank it
Expert:  Amedee replied 7 years ago.

Well, this is the wire that powers up the fuel injectors.


This wire needs to have power on it when cranking. Are you sure this relay is clicking?


If this relay is clicking and is in fact getting the ground signal from the computer to activate and it truly does have 2 powers going to it, this relay is bad and will need to be replaced.


If this relay is not being activated by the computer when cranking, then we will need to check the ground signal coming in from the computer on the Blue wire with Black stripe.

Expert:  Amedee replied 7 years ago.

The fuel injectors, located on the intake manifold near the cylinder head, are electrically operated, high impedance solenoid valves that open when energized. The injectors get battery power from the main relay when the ignition is in the either the "START" or "RUN" position, and are energized when the ECU completes the circuit to ground. Injection timing and duration is determined by the engine control unit. Injectors are energized either all at the same time once each crankshaft revolution (during cranking and cold engine operation), or in pairs (normal warm engine operation).

The injectors are constructed of stainless steel and high density plastic to resist corrosion. They consist of a fuel inlet with filter screen, an electrical solenoid and connector, and a pintle valve and nozzle. Injectors are held in place by the fuel rail and sealed by an O-ring and insulator.


Customer: replied 7 years ago.
ok no its not clicking i had my dad listen this time for me
.....but i just wanted to make sure you knew the fuel pump isnt getting power either not just the injectors does this control that too?
Expert:  Amedee replied 7 years ago.

NO... but lets do one thing at a time. Yes... I am aware of the fuel pump not getting power.


Is the computer grounding this relay when cranking on the blue wire with black stripe?


Is the computer even waking up? DOes the check engine light come on with the key in the on position? DO we have a 5 volt reference to the tps sensor with the key on?

Customer: replied 7 years ago.
yes the check engine light come on with the key in the on position,....there isnt 5 volts to the tps and there is just a blue wire coming from the it, it doesnt have a black strip...but they all have power except the black with yellow strip
Expert:  Amedee replied 7 years ago.

Ok... did you test the red wire for 5 volts at the tps sensor with the key on? This wire should have 5 volts.


At least one wire going to main relay should be getting grounded when cranking.


From what you are telling me, the computer is not doing its job.


We need to look at all the inputs to the computer with the key on and be sure it has all powers and grounds and that it is not being shorted out by any sensor. If all checks out good, the computer might just be bad.

Customer: replied 7 years ago.
yes i tested the red wire to the tps it does not have 5 volts and to test the comp do i just test with a test light or a volt meter.....if a volt meter what should it read?
Expert:  Amedee replied 7 years ago.

Here are two tests that will help you diagnose your problem. I do not think that these are what we have with your vehicle because we do not have fuel pressure because there is no power to the fuel pump....But its worth a shot.




1. Check for power to the fuel injectors on the Black/Yellow wire with the ignition on.

2. If there is no power to the fuel injectors, check the operation of the main relay and see if it gets turned on when the key is turned on. At the same time verify there is battery voltage to the main relay on the 2 Blue/White wires.

3. If the Engine Control Module (ECM) is not turning on the main relay, check for power from the "engine" fuse to the ECM on the Black/White wire.

4. If the main relay is turning on, check for an RPM signal to the ECM on the White wire from coil negative, while cranking the engine. If no RPM signal, check for a broken wire.

5. Last but not least, check ECM grounds on the Black and Black/Orange wires.


Potential Causes:


Burnt ENGINE Fuse
Main Relay



1. At the 4 wire connector about 6 inches away from the main relay, checking wires on the harness side of this connector, check the two Blue/White wires for battery voltage to the main relay.

2. At the 4 wire connector, check the Blue/Black wire for a ground through the Engine Control Module (ECM) with the key ON - look for less than 1.0 volt to be ok.

3. Check for battery voltage out of the main relay on the Black/Yellow wire at the 4 wire connector with the key ON. The Black/Yellow wire supplies battery voltage to the fuel injectors.


Potential Causes:


Defective Main Relay
Main Relay Wiring

Tips: The main relay supplies battery voltage to the fuel injectors. The main relay is located under the hood on the passenger fender. There is a 4 wire connector about 6 inches away from the main relay.

Expert:  Amedee replied 7 years ago.
TO test the computer we should use a voltmeter. But lets not worry about that yet. Lets run these other tests realy quick and let me know what you find!