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voltage drop

Discussion in 'Ford Trucks' started by Mr Patrick, Oct 10, 2006.

  1. Mr Patrick

    Mr Patrick Junior Member
    Messages: 26

    I have a 93 ford bronco 302. when driving at night with the lights on the volt meter drop whenI brake. during the day it does not move.any idea what is causing thi thanks Patrick
     
  2. THEGOLDPRO

    THEGOLDPRO PlowSite Veteran
    Messages: 3,136

    prolly a bad alternator, it drops when you put a load on it, IE: lights,radio, heat, brake lights. and so on and so forth.
     
  3. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    How much of a drop?
    With the lights on you draw about 14 amps to light all of them. Add the brake lights which I would bet pull over 5 amps you have a draw of near 20 amps.
    I would bet the Bronco has a 60 amp alternator. At idle you only put of about a 1/3 of it's rating ---> 20 amps. The system starts to pull from the battery so you see the drop to battery voltage. The alternator should be putting out 13.5 -- 14.5 volts when running. The battery 12.6 or so volts when not running.
    Most auto parts places will test your charging system for free.
     
  4. 04superduty

    04superduty PlowSite.com Addict
    Messages: 1,354

    in older vehicles the lights dimming at a stop light was common. like mickirig said the alternators were basically just adequate for the load. now with modern vehicles having a huge amount of current draw from accessoires is why most have much bigger alternator(s). heck some ford taurus's have 130 amp stock.
    if you think there is a problem pull the alternator and take it to auto zone or any of the other parts stores. most if not all of them offer a free check.
    you could also just drive your bronco and they can ckeck alot of the charging system and battery out for you.
     
  5. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    My 2000 Windstar has a 140 amp and a battery that looks like it belongs in a tractor trailer rig. It's huge right from the factory!
     
  6. Mr Patrick

    Mr Patrick Junior Member
    Messages: 26

    Thanks for all the advise I had a vat test done at the shop and all the load leavals were fine
    I have a 160 amp alt ready to go in but I was wondering if the external voltage regulator might be the problem any thought? thanks Patrick
     
  7. 04superduty

    04superduty PlowSite.com Addict
    Messages: 1,354

    if they load tested your alt while it was still mounted in your truck and it did fine than the voltage regulator is fine. make sure that your new alt is not internally regulated. if you do put that larger alt in you need to increase the size of the wire that goes from your alt to batt.
     
  8. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    If it has an external regulator and it's not been changed yet. You need to have the Heavy Duty one. The regular duty is not designed for the constant demands of plowing and long time periods of charging. LIke they said you have to upgrade the size of wire leading to the circuits the alternator supplies. If not the wires will overheat. You don't want a wire to fry in the middle of a wire harness. That would make your day!
    I have seen it happen.