Charging light on, brake light on, fuel light on - No A/C fan

[MrMGA]

There was a thread on this before, but the right solution was not posted. (I don't *think* it is the alternator.) I'm trying again with a more descriptive subject line. This is regarding my '95 Rodeo.

Three dummy lights - charging, brakes & fuel - were turning on and off sporadically. Now they are stuck on and the A/C-heater fan does not work. Previous posts say this is the sign of a bad alternator, but I have replaced the alternator twice and have the same problem. The second alternator was purchased from an Isuzu dealer at considerable expense. I had it tested at two shops today and each said the alternator is fine. One guy says he suspects a bad ECM. The other guy says it sounds like a bad ground somewhere. Before I spend more $$ on this problem (I'm already out $600 on the alternators), I'm again seeking advice from Forum members. A search of Forum messages turns up several posts about this problem. Others have had the same identical problem. Some solved it by replacing the alternator, but mine tested out OK. Has anybody had the same problem and found a different cause? Help!

[rodeo02]

I don't wanna beat a dead horse , but have you verified 14VDC across the battery terminals with the truck idling? You can get a decent digital multimeter for under $20 to do this (you can ONLY verify this with a multimeter. Not the dash gauge) You could have a failing battery, a battery cable corroded or broken under the insulation, or like you say, a weak ground somewhere.
G/luck
Joel

[2eyefishclaw]

not sure if this model has it but the charge relay in the pdc can cause these symptoms

[TheFugitiveMind]

i have a multimeter how can i test how many volts are going through my car? i think my alternator is on the way out. its a 01 passport with about 50k miles. everytime i roll down the windows at idle it seems to struggle and if the headlights are on they dim a little bit

thanks

[MrMGA]

Originally Posted by rodeo02

I don't wanna beat a dead horse , but have you verified 14VDC across the battery terminals with the truck idling? You could have a failing battery, a battery cable corroded or broken under the insulation, or like you say, a weak ground somewhere.
G/luck
Joel

I forgot to mention that the battery is brand new. I didn't specifically ask each mechanic if they saw 14 volts, but each said the battery and alternator were working fine.

[MrMGA]

Originally Posted by 2eyefishclaw

not sure if this model has it but the charge relay in the pdc can cause these symptoms

What is the pdc?

[steveb_92rodeo]

Originally Posted by TheFugitiveMind

i have a multimeter how can i test how many volts are going through my car? i think my alternator is on the way out. its a 01 passport with about 50k miles. everytime i roll down the windows at idle it seems to struggle and if the headlights are on they dim a little bit

thanks

To test vehicle voltage...

First, ensure your multimeter is set to 20v DC.

Then, with the vehicle off, put the + (red) voltmeter lead on the positive battery terminal, and the - (black) lead on the negative terminal. Record the voltage.

Then fire up the vehicle, and while it is idling, do the same thing with the voltmeter again. The battery when the vehicle is off, should show about 12v. While idling, it should increase to 14+.

If you are not getting ~14v while the vehicle is running whether consistant or not, you should look for bad cabling, loose battery terminals, corroded or loose grounds, and finally the alternator itself.

HTH,

Steve

[2eyefishclaw]

PDC = Power Distribution Center (fuse/relay box under hood) if it is equipped on this model, if memory serves correct the relay will be brown