Alright guys, here we go.
I've got my '85 Econoline 150 with a 5.0 and a 2bbl. I finally decided to dish out the 300 for a new carb, the crazy thing has an 02 sensor and all. Well now that I get all that worked out, the electrical goes on me. (Did I mention that before the carb started acting up, the brakes would sporadically go out on me?)

So here we go, I'm driving 35 down to work, and my alternator light is flashing on and off with no apparent rhyme or reason. Now it does this at idle as well. So I figure since its not always at idle, just a belt. Well I rev the heck outta the motor to see if its just slipping at low rpm's. Not the case. Now it gets worse and the light is staying on constantly. Occasionally it'll go out, and then it finally came back on and stayed on. I figured it may be a bad battery, but nope, replaced it and it was still a problem. Bad alternator, nope, replaced it still a problem. Voltage Regulator, replaced. Starter solenoid, replaced. I am so lost right now. Please tell me that it may still be the regulator. I'm getting twelve volts down at the positive wire on the alternator, and I've bench tested the alternators and they all came out good, even the old one. I work at Pep Boys and I had some guys in the shop (I'm only 17 and work at the parts counter, I know usually you get 17 year olds who dont know what they're talking about, but come to mine and you won't be dissapointed. It's not like you remembered before, but we're not all too bad.) troubleshoot it with me and we were just baffled. Some are saying the starter might be drawing too much current, but that wouldnt make sense as the starter is disconnected after the vehicle is running. Please help. Thanks

Carlo Jr.

 

Best guess.......... check the wiring and connector on the voltage regulator...make sure the contacts are clean and not corroded. Also check the connections on the alternator and at the battery + connection on the starter solenoid/relay.

 

I would install a voltmeter. Also try connecting the S terminal on the regulator to +12 and see if the alternator starts charging.

 

A voltmeter could tell you things. The connector to the regulator is often loose or coroded.

 

Thanks guys, but those are some things i forgot to say I tested. We checked voltage drops along the lines, but we hadn't tried the jumping the s terminal. I'm off to take a look at that now. Please keep the ideas coming.

 

Well thanks guys, I went through and it was undoubtedly the S terminal of the regulator. I was ripping my hair out at the thought of paying over 200 to get it fixed. It's not easy paying 2100 a year for justliability insurance, and going to school, and trying to save up for a new car. My parents are doing it the right way though, it sure is teaching me to be responsible with my money. Thanks so much guys, it's great to have people online who try and help out other guys. This is an awesome community.

 

A truck with an ammeter uses +12 from the ignition switch run terminal to the S terminal to activate the regulator. The idiot light setup is different. A quick check of the regulator is to see if it is supplying voltage to the field term of the alternator. I think newer alternators get a ground signal to the field. Same kind of operation, just reversed.