'94 3.0L Draws voltage down to 0.5V when key is turned on

[AirNWater]

I have a '94 3.0L (Manual Transmission) 4x4 Ranger that I've been rebuilding. It has been starting just fine until last night. When I tried to start it, everything went dead - no dash gauges, no lights, no fuel pump sounds, nothing. I made sure the battery was fully charged. I put a volt meter across the fuse panel in the engine compartment and it reads 12.5V with nothing on. When I turn the ignition switch on, the voltage drops down to 0.5V. When I turn the switch off, the voltage jumps back back up.

Trying to track down wiring using the Haynes Manual is nearly impossible - they don't even list the fuses I have in my engine bay fuse panel. I've tried pulling the 3 relays in the engine bay fuse box (fuel pump, PCM power and AC WOT), but still get same results. Have also tried pulling all the fuses from both fuse panels (engine bay and interior), but can't seem to isolate what is drawing down the power! I've tried disconnecting the alternator power wire just in case it was shorted diodes with out any luck.

Can anyone suggest where to find a better wiring diagram, that actually shows power connections in the fuse panels, along with actual switch contacts? Boxes with wires going in/out but no other details don't help much.

Any other suggestions on what to try/test?

 

[Curious Hound]

The wiring diagrams in the tech articles here are pretty good. The files are labeled for different years. But I have found them to work pretty well so far for my '93. They should get you close.

Can you try a different battery? You may have a bad cell that looks good with open circuit but just can't handle any load. If it's a circuit issue, you should have been able to narrow it down by pulling fuses one at a time.

Sent from my SM-G920V using Tapatalk

 

[AirNWater]

Eric,

Thanks for the ideas.

I have tried a different battery with the same results. I guess I'm down to pulling every fuse and see if I still get the same results, If not, then I'll plug them back in 1 at a time until I see the problem again.

 

[Doofy]

Bad connection at battery or starter relay. Bad ground?

 

[RonD]

12volts is only 12volts if there is 0Volt reference, 0volts is the Ground.

While checking the fuse power(12.5v) where are you Grounding the meter?

Check battery ground cable at engine end
And battery positive cable to engine fuse box

You can't go from 12.5v to .5v without seeing smoke, so it isn't a short, volts or Ground is disconnecting

 

[AirNWater]

Ron,

The meter negative lead is connected directly to the Negative terminal of the battery. Not seeing any smoke. Will double check the connections tomorrow, but I've replaced the battery ends of the cables and am fairly confident of the fuse and engine connections.

Thanks

 

[Pauls 4x4]

I had a Buick once melt the ground wire and cause such an issue. No switch power at all though sounds like a starter selonid or bad ignition. My ignition is all kinds of hot wired because it all rotted in there.
If you had a draw the tac. and other lights flicker. It sounds like switch power is working (you get the drop) but it's all going to a high capacity draw (starter, etc.) that wouldn't smoke.

 

[RonD]

Use the engine as the ground, that helps test the battery cables connection.

No smoke means you are not looking for a short, you are looking for a bad/corroded connection

 

[Andy D]

Use the engine as the ground, that helps test the battery cables connection.

No smoke means you are not looking for a short, you are looking for a bad/corroded connection

Heh heh Shorts are easier to find. Opens are cheaper to fix, usually

 

[pjtoledo]

start over at the beginning, put test leads directly on the battery terminals.
then move one test lead to the cable attached to the battery, then follow the cable and test the other end, then what it attaches to

repeat using the other terminal.

since the starter only drops a battery to 11-10 volts, the amount of current needed to pull it all the way down to .5 would result in LOTS of smoke in about 1 second.
as previously stated, you have a bad or corroded connection. its not letting enough current thru to maintain the voltage.

 

[AirNWater]

PJ & Ron

Looks like you guys were right on the money. It appears as though I had a bad/loose connection on the positive battery terminal that I had replaced a number of months ago. I took the wire out, re-cleaned it, and reattached it and the issue seems to be gone. I've been able to start it 5 or 6 times in a row without it reoccurring!

Thanks for the suggestions and help!

 

[Curious Hound]

Glad you found the problem.

 

[RonD]

Good work

Thanks for posting the fix