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Headlights dim as I apply the brake...

S

ScottyDog

NAXJA Member #631
Location
Gardena(90247), SoCal Where the 91/405/110 Fwys co
Its an 88 MJ. The battery died as it has been sitting for a couple of weeks. We jump started it and drove it around last night for about 15 minutes but the elec guage wouldn't read anything above 9 volts. And the lights dimmed when we applied the brake.

But this morning the truck started up no problem and the electrical read a fully charged battery of 14 volts..... Could the guage cluster be acting up?? Also what would cause the headlights to dim when pressing on the brakes??

Any help would be greatly appreciated.

Thanks,Scott
 
Bad battery? Try seeing if you can get the battery to charge with a battery charger.
 
sounds like an alternator issue. maybe the regulator on it is going out. your lights dimmed because the brake lights were drawing current and your battery was too weak to light both properly. could also be just a bad battery
 
My headlights dim on my '89 4.0 when I use any sort of current drawing apperatus. Back wiper, fog lights, HVAC fan, brake lights, etc. Not by a huge amount, but noticable if you're paying attention. New battery and it reads 14.9 volts with the headlights and HVAC fan on full blast.

I believe it's caused by a worn or loose belt. As soon as you put a load on the alternator, the belt might slip and the alternator would put less amps out until it catches up again and stops slipping. Would also explain my belt squeel. Could be your problem too.
 
Doesn't the Alt. spin at the same speed (engine RPM) all the time. Turning on an accesory shouldn't "put a load" on the alternator except in an electrical sense, not more pull physically. Seems to me the only things that might do that are the A/C pump or maybe the P/S pump at a full turn.
 
ParadiseXJ said:
Doesn't the Alt. spin at the same speed (engine RPM) all the time. Turning on an accesory shouldn't "put a load" on the alternator except in an electrical sense, not more pull physically. Seems to me the only things that might do that are the A/C pump or maybe the P/S pump at a full turn.
Click to expand...

Oh yes it does. Ever do the hand-cranked generator thing in science class? It cranks easily with no load and the more load you put on it, the harder it is to crank.

:cheers:
 
Ditto on the grounds, and maybe time to upgrade batt cables.
 
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