Electrical Issue?

[stebbiro]

I have a 1999 4WD Ford Explorer XLT 4.0 SOHC.
The speedometer started jumping around as I was pulling into a store.
When I came out, the truck wouldn't start. I pulled the key, checked to see if it was in park, then restarted it.
Everything was fine, but the radio had reset.
This morning, I started it and everything seemed fine, but the heater/defroster would not kick on.
Any ideas on where I should look first?

 

[J_C]

I'd start assuming you had a low voltage problem which made the electronics go haywire and reset the radio.

Possible culprits include corroded battery terminals, a bad alternator, or when in the off state your battery may have some bad cells in it. Consider the battery age, but you can use a multimeter to check voltage and if it's not a maintenance free battery, if the vent caps pop off you can put copper wire on multimeter probes (so the battery acid doesn't eat up the multimeter probe tips) and test the voltage between each cell of the battery to see if any are dead.

The battery should be at around 12.6V shortly after the engine is off, and around 14.4V running. Lower than 12.6 off is most likely a bad battery (unless the alternator Just Failed and didn't charge the battery). Lower than 14.4V on is more likely a bad alternator but a bad battery can keep the voltage lower too and cook the battery.

What about the heater/defrost didn't work? It might be coincidence. Did the blower spin, you got airflow but no heat or out the wrong vents or ??? Do you have automatic climate control with a digital console display? If so that could have a problem with low voltage too.

If your battery voltage off isn't close to 12.6V, I'd put a battery charger on it and see if it gets to 12.6V and stays near there after the charger is disconnected. If it doesn't, bad battery. If it does and drops voltage again running, bad alternator.

Do check the battery terminals for corrosion first, since that's a cheap/easy fix most of the time.

 

[roscoe 0202]

check the battery cables usually if they are going they will swell under the insulation
roscoe

 

[AWD96spoon]

I had the a similar issue, was able to temporarily fix it by tightening my battery cables but in the end it turned out to be my alternator.

 

[stebbiro]

O.k., I chased this down and believe I had both the blower motor and the alternator going at once.
I checked the battery connections and only found a small amount of corrosion between the negative cable connector and terminal.
I cleaned that left it off for a bit as I hear that solves some ghost problems. I put a meter on it and had 12.6-9 after I checked with the engine on and had 14.8vdc while running.
I turned the heat on and rapped on the blower motor with my ratchet and whaa laa! heat! So I got a new blower motor today.
The reason I believe the alternator is going bad is the power reset that happened when the speedometer went nuts, also there is a whine from the alternator.
Glad I got heat... It snowed the day after it broke! Go figure.

 

[RandomNerd2000]

Even though you seemingly have a solution, considering we're nearing winter, have you had your battery tested? Batteries do need load testing, especially with the winter months at hand, I have all mine tested/replace as needed annually, if it did test bad or weak, Walmart has a ValueStart battery for $50 I've had good luck with, I've got several of them for myself and friends and none have issues.

 

[AWD96spoon]

Make sure the blower motor circuit has the correct fuse in it. If someone has put an oversized fuse in it then it could have pulled down your whole system without popping the fuse. If a winding in the blower motor was going to ground it would pull about 5x your normal operating current which would probably be enough to cause your speedo to not have to power needed to work accurately And quote possibly keep the truck from starting, especially if the battery is a little weak to begin with. I've seen people jumper a piece of wire in place of a fuse that keeps blowing. If the blower motor is bad and it's not just a poor conection somewhere then it should have popped the fuse.

 

[J_C]

^ A bad blower motor won't necessarily blow the fuse. Worn out brushes or a bad spot on the commutator could both make it fail without excessive current.

IF the blower motor was shorting out, enough to pull down the whole electrical system, then I would inspect the wiring too because pulling that much current should have charred some wire insulation at the very least.

 

[AWD96spoon]

^ A bad blower motor won't necessarily blow the fuse. Worn out brushes or a bad spot on the commutator could both make it fail without excessive current.

IF the blower motor was shorting out, enough to pull down the whole electrical system, then I would inspect the wiring too because pulling that much current should have charred some wire insulation at the very least.

You are correct, I forget we are talking about a dc motor. The ones I work with at work are all 3 phase AC induction motors so they fail a little differently.

 

[donalds]

You are correct, I forget we are talking about a dc motor. The ones I work with at work are all 3 phase AC induction motors so they fail a little differently.

Now if only we could put a frequency drive on that bad boy eh