starter motor and ignition issue

[Zeus]

Started her up after about a month of it not running this past July. Drove her across town maybe 10 minutes to the store. when i came back to the parking lot and turned the key i get a single click from the starter solenoid. I hastily buy two new batteries as it was a friday evening nearing closing time for the auto parts store. replaced the batteries and still got the single click at the starter, i decide to give the starter motor couple bangs to see if it helps but no luck. As it got dark out, i called a tow and got her home, when the tow pulled up to the house i rolled her off the flat bed in 2nd gear and she started right up. i didnt get around to working on the problem until september. i ordered a new starter from amazon, verified operation with a good battery and then installed it, still got the single click from the solenoid. i got my meter and started checking voltage, battery voltage 12.7, i put my black lead on negative post of the battery and read 10.8 volts at the starter motor signal wire terminal when turning the key to start position. black lead remains on negative post of battery i read 11.5 volts at pin 87 of the starter relay, thats the wire that goes to the S post of starter motor from the starter relay in the PDC. i checked voltage throughout the signal wire the runs from pin 87 to the S post of starter motor by poking it and read voltage drop of .2 or .3 every foot or two and felt the wire warm up while turning key to start position. i replaced the signal wire with a 10 gauge wire from the relay, i repinned the 87 terminal in the PDC, still no luck just the single click when i turn the key to start. checked voltage of the ignition signal wire that enters pin 86 of the starter relay i read 12 volts, battery voltage is 12.7. checked voltage at the key ignition module where the 7 connection terminal block connects to the key ignition module. im getting 12 volts at the yellow wire but the red fused battery wire gets battery voltage and the other 4 wires' voltage at the terminal for the ignition module under the steering wheel checks out in the run position in the acc position but when i turn the key to start and check the yellow start wire i get .5 voltage drop all the way to the starter relay at pin 85 and then across the relay, as i mentioned already, the 87 pin signal wire drops another .5 volts until it gets the S post where it drops again another .5 volts. I question if the my ignition module is bad and not getting all the necessary volts to the yellow key start wire ? And if that is the case then why does voltage continue to drop across the starter relay and then again down at the S post of the starter motor? Ive replaced the starter motor, the starter signal wire, the starter relay, the batteries are charged all cables and connections are cleaned up. Ive checked my grounds at the starter motor housing and at the starter relay in the PDC and the grounds are fine. Is it just my key ignition module thats bad or am i missing something? Any and all help is appreciated, ive tried to do my due diligence and ive been at this for 2 months whenever i get the time.

Edited October 27 by Zeus

[Tractorman]

Have you checked the condition of the 30 amp fuse in the PDC? 

 

I would make a 10 gauge jumper wire with a terminal connector on one end that will fit into terminal #87 relay base in the PDC.  Place the transmission into neutral and set the park brake before doing the next step.

 

Insert that connector into #87 (relay base in PDC) and touch the other end of the jumper wire to the positive post of the battery.  If the starter cranks, then you have narrowed down the problem area to be somewhere between the battery connection and the terminal #30 of the starter relay, which would include the 30 amp fuse in the PDC and associated wiring.

 

  If it still doesn't crank, I would be looking for a ground issue between the engine block and the battery.

 

- John

 

[Zeus]

Ive checked all the fuses and grounds with a meter, but I'll check the fuses again and will consider replacing the 30 amp fuse. i cleaned up the engine grounds from both batteries, brushed and cleaned the battery connected cable ends, cut back any corrosion and re-crimped all battery connections with ring terminals, and replaced the clamp style connections to a side post setup. The starter relay ground pin 85 shows good grounding as well when check it across the battery positive post.

[Tractorman]

I don't know how you are using your meter to check continuity for grounds, but if you are testing using the ohmmeter, then the test results will never be conclusive.  All it takes is the connection of one strand of a wire to show good continuity.  Performing voltage drop tests under load would provide much better information. 

 

You sound like you are comfortable using a multi-meter.   Many people that I know who have used multi-meters for a long time have drawn wrong conclusions when using the ohmmeter for testing, or using the voltmeter without an electrical load being applied.  Again, it only takes a single wire strand to read continuity or 12 volts.  This is one reason I use an incandescent bulb test light for testing circuits - the bulb imposes a small electrical load and will readily dim if the circuit being tested has a fault.

 

Have you tried the jumper test that I recommended?  I think this test would be the fastest and most conclusive test to perform.

 

- John

[Zeus]

Im using DC volts to check grounds when turning key to start, i get no signifiant voltage drop readings, and i use continuity and visual inspection to check fuses. I have tried to jump out the 87 pin on the starter relay and no luck just a single click. 

[Tractorman]

3 hours ago, Zeus said:

I have tried to jump out the 87 pin on the starter relay and no luck just a single click. 

 

Bypass the #87 pin and jumper directly from the battery positive post to the "S" terminal on the starter.  If the symptom remains the same, then there can be only one of three potential issues.  This is assuming that your batteries are fully charged and are in good operating condition (which they should be).

 

1.  Poor connection / cable from the battery positive post to the starter.

 

2.  Poor connection / cable from the engine block to negative post of battery.

 

3.  There is an internal problem with the replacement starter.

 

- John

[Zeus]

i understand but don't you think there maybe something to do with the yellow key start wire from the ignition module. I am getting .5 volts less than battery voltage at the yellow connector that goes into the ignition module when i turn the key to start and then another 1 volt less than battery voltage across the starter relay at the number 87 pin signal wire to starter motor.

[Tractorman]

Your signature says that your truck is a '99.  The wiring diagram that I posted is from my 2002 FSM, but I believe the diagram is correct for a '99.  Maybe you can verify. 

 

When you used the jumper from the positive battery post to terminal #87 in the relay base, you bypassed the ignition switch, clutch safety switch, starter relay, and the 30 amp fuse in the PDC.   Since the symptom remained the same (a single click), you have essentially eliminated all of those components and associated wiring from being the problem. 

 

Continue with testing in the manner recommended in my previous post and you will narrow down the problem area even further.

 

- John

Edited October 27 by Tractorman