I have a `91 Explorer that has me a bit baffled.

Currently it only has dim interior lights. The headlights will not come on and the starter will not engage. If I jump the starter relay (on inner fender next to battery) I only get it to click – nothing else. I have pulled the starter and the battery and had them both checked. Both are good.

Any ideas as to the next logical item to check? Many thanks,

Mark

 

Next logical item to check (IMO): battery cables and connections. Best done by measuring the voltage drop across the cables, since corroded cables may not be visibly apparent. They can corrode internally.

 

I have measured the voltage of the battery at its posts at 12.8 and down at the starter connection and it too reads 12.8V with my negative lead grounded to the engine block. Is that measuring how you are suggesting or is there another way?

Many thanks,

Mark

 

One thing that you could try is to add a jumper cable between positve post on the battery & starter relay etc & see if it will crank.

 

That's only half the story. The battery + cable splits; one wire goes to the starter and the other goes to the solenoid on the fender. This is where the fuse distribution box gets its power. The fact that you don't have headlights indicates this is not a starter problem. Turn headlights on and check for power on the 30A & 40A fuses.

The wire from bat + to solenoid is known to go bad at bat term. Jumpers from block to body also go bad. With load like headlights check to see that there is no more than 0.2V between bat - and body.

You should be able to jumper the two large terminals on the fender starter solenoid and cause the engine to crank even without ignition key.

 

87 XLT

So that the jumper cable would act as a temporary battery cable?

Mark

 

Opera House,

When I jumper the fender starter solenoid it only clicks, no starter action.

Mark

 

I have no idea what you are jumpering; two big terminals or one big terminal to the little one on the solenoid. And when you jumper it to another vehicle,where do you make connections to make it crank. Makes a big difference if you make the jumper connection to the block or battery -. I think the solution is getting the lights to work.

 

Opera House,

I am jumpering between the one big post and the small one on the fender solenoid. With the battery connected as noraml, I only get a click from the fender solenoid. This only means to me that the solenoid is in fact working. But, it does not cause the starter to crank.

I have not tried to jump start it from another vehicle but if I did I would connect both bat + with jumper cable and engine block or chassis to engine block or chassis.

Mark

 

You can try jumpering the two large posts on the fender solenoid and that should get it to crank. This supplies only about 12A to the solenoid on the starter. Though interesting, working on the starter circuit is a waste of time. The answer to the real problem will be found by workin on the lights.

 

I see that Opera house works mentioned that the cable between positive on battery & the solenoid/starter relay can go open.Just double up this connection with a jumper cable. Jumper cable as what you what you would use to jump start from another car. I see from what Opera house works sez that Ford has changed the way this is wired from how my 87 is wired & not for the better. It would be nice if they would leave well enough alone.

 

To check the lights as you suggested in your first post, are the 30A and 40A fuses in the box located on the inner fender or the fuse box under the dash?

Many thanks,

Mark

 

Yes, it is right next to the solenoind. The following procedure may help.

General Electrical Diagnostics
To diagnose electrical problems, always have the same reference point. Remove the battery terminal from the negative post. Clean the post and the connector. Then reattach and tighten. This will insure that this one connection is good. All voltage measurements should be made from this electrical terminal.

1. With the engine off, turn on the headlights to create a current load of about 20 amps. Bad connections have resistance and a voltage is developed when a current is passed through them. If headlights do not turn on go to step 3.

2.With headlights on and engine off, measure the voltage from the NEG battery terminal to the vehicle body. This should be some place that does not have a wire going to it. If voltage is greater than 0.25 volts then there is a grounding problem..

NOTE: The negative terminal of the battery is normally connected to the engine block. There may also be a smaller wire that connects to the body. Engines are electrically isolated from the frame and body. There are an additional two to three ground straps that connect the engine to the body and frame. These straps can corrode and break. Then the only connection is through bearings that have higher resistance and can be intermittent. There should be always at least two current paths. When you find one that has failed, there is also another one that has failed. Add that extra ground strap to have reliable operation.

3. Measure the voltage from the NEG battery terminal to the POS center post of the battery and record the voltage. Voltage below 12V indicates a discharged battery. If above 11V you can continue testing. Now measure the voltage on the battery connector. This voltage should be exactly the same.

NOTE: The positive terminal of the battery is normally connected to the starter terminal. There will also be a smaller wire that connects +12 volts to a power distribution point. This will be the starter solenoid (relay) on the fender. Power to the fuse block and output from the alternator connects here. Typical battery voltage with the engine off is 12.5 to 12.8 volts.

4. Measure the voltage from the NEG battery terminal to the stud on power distribution point (solenoid). This voltage should not be lower than 0.1V below that measured at the battery.

5. Measure the voltage from the NEG battery terminal to the main (40A) fuse in the distribution box. This voltage should not be lower than 0.2V below that measured at the battery. Measure this voltage on both sides of the fuse. Check the manual for the correct fuse location. Headlights may be turned off if the problem has been found.

NOTE: Fuses have a holes in the top just over the pins. If the probe will not fit in, use a pin or an awl to make contact. Some fuses have switched power. You will either have a normal 12V or nothing. If you see a voltage in between, there is a wiring problem.

6. Measure the voltage (engine not running) from the NEG battery terminal to the stud output of the alternator. Don't slip with the probe, this terminal can supply a lot of current. This voltage should not be lower than 0.1V below that measured at the battery. If no voltage is present, the fuseable link between the alternator and distribution point has blown .

7. Turn the ignition key on but do not start the vehicle. The battery idiot light should be on. The alternator regulator is turned on through this lamp. If the lamp doesn't light there could be a loose connector on the dash. In the dash there is a resistor across this lamp. In the unlikely event the lamp fails, the alternator will continue to charge. Measured at the alternator plug, the lamp LG/R wire should have greater than 0.2V with the ignition on. A 470 ohm ½ watt resistor from this pin to a switched 12V source will serve as a temporary fix to operate the alternator.

8. Measured at the alternator plug, the regulator 12V power Y/W wire should have the approximate battery voltage. This is powered at all times. If nominal battery voltage is not present, check the 15A regulator fuse in the distribution box.

9. Start the vehicle. Measure the voltage from the NEG battery terminal to the POS terminal of the battery. If the alternator is charging the voltage should be over 13.5 volts. Turn the headlights on and verify the voltage is at least 13.2 volts. Even an alternator with a defective regulator can put out small amounts of current from residual magnetism in the rotor. Voltage of over 14.5 volts indicates an overcharging condition.

 

Thanks OHW. Hopefully I can get some time this evening to start chasing this down using your thorough guide.

Many thanks,

Mark

 

Have you ever thought of getting a newer vehicle?

Mason