Been struggling with this electrical issue for a week now and have made numerous searches in this forum but still haven't been able to figure it out. I don't drive my truck (1999 F-250 7.3L w/135K miles) very often and went out last week to start it and immediately could tell that it didn't have enough voltage to start (low dome light, fading WTS light, etc.) I pulled both batteries to charge but when I hooked them to the charger, they both had full charges. Re-installed the batteries and turned the key and had absolutely nothing. Gauges didn't move, no pump running, no lights, no radio, nothing. This morning I used a meter to test the battery voltage and have 11.6v. Also have 11.6v at the Power Distribution Box. The inside fuse terminal, with the ignition on, has between 3.6v and 4.2v depending on which fuse I test. I pulled and checked all fuses with a meter and also tightened the firewall bolt on the PCM which was a little loose but not too much (maybe 1 1/2 turns). I should also mention that I have had the seemingly common problem of water leaking through my windshield seal on the driver's side which has caused the horn to sound, turned on my dome light, caused it not to start on one occasion, etc. Any suggestions or advice would be welcome and much appreciated before I load it on a flatbed and take it to an automotive electrical specialist to figure out. Thanks.

 

A battery at 11.6v is dead! You need new batteries or a charge. A superduty will not start with that voltage, it needs almost 11 while cranking(cant remember the exact#)or it won't fire the injectors.A good battery should have aprox 12.5 just sitting. You also may have a bad connection or a short in the truck also.

 

What he said ...you need TWO new batteries. A fully charged good battery should be about 13 volts. As soon as you turn the key on I bet the batteries you have read way below 11 volts...maybe less . You need 10.5 V for the PCM to command injectors to fire and lots of amperage to crank a cold hunk of steel that big against the diesel compression. Oh, and get the windshield resealed...

 

I figured even if the batteries were shot I should still get something. I just tested voltage of the batteries with the ignition on and it dropped to 4.3v. Purchased these two Interstate batteries in Oct 2010 so maybe I have some other problem that is draining my batteries. Any advice on where to get some decent battery cables? The Ford cables seem to be WAY overpriced. Thanks for the help.

 

Get some welding cable and make your own. You can get all the parts on line for the ends. Some on here have posted them, I'm just not good at that.

Chet

 

Thanks Chet. I'll do a search for making the cables.

 

Both batteries were bad so I installed two new Interstate batteries, replaced all three battery cables and checked every fuse. Also removed the under dash fuse panel and cleaned all connections which were pretty bad from the leaking windshield. Now all lights and gauges work, WTS light cycles and the vacuum pump runs but I get nothing when I turn the key to start. Any other suggestions before I'm forced to call for a tow truck?

 

Bad starter> Pull it and check it out first.

Chet

 

Try banging the starter a few times. They can get stuck from time to time. It wouldn't hurt and it just might let you know what your problem is

 

Here is the wiring diagram for your starter circuit:



Check the ignition switch first, you should see 12V on fuse 20 (15A) in the under dash fuse panel with the switch in the start position.

If that's good then check the neutral or clutch position safety switch. You should see 12V at the starter motor relay coil wire (on the passenger side fender) with the ignition switch in the start position. The wire will be tan/red (automatic) or dark blue/orange (manual).

If that's good then check the starter motor relay. You should see 12 V on both large terminals (red and yellow/blue) with the ignition switch in the start position.

If all of that's good then check the starter.

Chris

 

You could try treating the shift lever (auto?) like the handle on a toilet when it keeps running. Jiggle it by going between Park and Neutral.

 

Quite possible! We have a truck at work that has that problem! We have to shift it between the two sometimes to get it to start!

 

First of all, thanks for all the help; I think we're getting closer.

Fuse 20 has 12V at all times. Is this wrong?

The lower terminal on on the starter motor relay coil? (on the passenger fender) also has 12V at all times. The upper terminal never registered voltage.

The terminal with the red wire on the starter motor relay (on top behind the fuel/water separator) has 12V continuous. The terminal with the blue and yellow wires has 12V when the key is turned to the start position.

The terminal on the starter with large red wire directly from the battery reads 12V continuous. The other two terminals never registered anything.

My son helped me with the battery cables. I was under the truck when he connected the harness to the two terminals on the starter motor relay (passenger fender), he couldn't remember where tan/red wire connected to. Based on the routing and position of the wire, it appeared to only reach the lower terminal. Was this correct?

I also wiggled the drive selector handle and also tried starting in neutral with no success.

 

The relays on top of the motor behind the fuel filter are for glow plugs and air intake heater (if it's a late 99). They don't ahve anything to do with the starter.

Chris