'87 Bronco Battery/Alternator/Electrical questions

Hi All,

Just stumbled upon this site, and I think I may become a regular visitor. My daily driver is out for extensive repairs, so the '87 Bronco which is used primarily to haul a horse trailer is now my daily steed. 

I see now why heated and remote control mirrors were invented. But, on to the main questions:

First, I am the third owner of this Bronco. It was obsessively maintained by the previous two owners (one brothe sold it to another, then to me) and sadly, I have been a bit less vigilant in learning what I should know about this vehicle.

I have been reading up on parasitic draws, I have one, I don't bother this thread with that, I have some leads to follow.

Main issues now: what should the battery meter read at idle and at maximum draw (headlights, heater fan, radio)? With just the radio on, the in-dash meter is reading 13.5v, and with lights on, it dips to 12.0-12.5 v.

At idle, with a freshly charged battery I get 14.0 v. using the Schumacher battery charger/tester, but I may also be reading some static charge also,so I  need to retest tonight.

This feels like a flakey alternator to me, but I don't know what correct outputs should be for this vehicle.

Second issue: There is a trailer brake installed. When I press on the brake, WITH THE POWER OFF AND THE KEY OUT OF THE IGNITION, the radio comes on. The radio is the standard Ford-branded radio, so I assume this was wired in correctly. Is this a "feature" of the Bronco, or is the trailer brake causing some wierdness? This is my thought, but again, I don't know all the features of this vehicle well enough to have an informed opinion.

Thx!!

Hi Pier.., welcome..!

Does your charger load test..? If not, fully charge the batt. & have it tested at auto parts store for free.

If it's OK.., it's likely the alternator is getting weak.

They can test it as well.

Having said that.., those readings you're getting could be up to spec.  I don't know.

You could use a volt meter on the batt. terminals to see if the dash meter is reading correctly.

Also higher RPM's may raise the readings.

I don't think alternators put out full power at idle.

Sounds like an aftermarket trailer brake and it was poorly wired & feeding back 12v into radio + wire.

I doubt the radio comes on (brake pressed) with the **** turned to the OFF position. .?

Hi Bully!

Thanks for the info. The battery is new - as in one week old. I had not tended the battery that was in the Bronco for a couple of months (ooopppssss)and it was stone dead and would not take a charge.

So, the battery itself is good.

The radio comes on when the radio has been left ON but the engine turned off and the ignition key removed. Yes, the trailer brake is aftermarket, I don't know who did the original install. I will check on what the radio does when it is turned OFF at the radio.

My charger does not load test. It was a $100 Schumacher special which does all the thinking for me, which means I have no idea what is going on. When set to the "% Alternator" mode, it reads 110%. The manual says that the readings can be anywhere from 1-199, which of course does not help me, save that the manual says that a reading of 199 does NOT mean the alternator is producing twice as much power as it should. My take on this is that a reading of 110% indicates that the alt is failing, but not yet given up the ghost. And, it is POSSIBLE that the electics in the alternator may be the source of my power leak. I guess after 28 years, things tend to get a bit wonky.

(As an irrelevant aside: I had a an alternator replaced on my 2002 VW New Beetle -- do NOT ask what THAT involved)

(Well, OK...the entire front end of the Bug had to come off, since the alt is tucked down in the lower part of the engine compartment. And at that, the alternator was fine, it just had a frozen clutch pulley that was mucking up the serp belt. And,VW being VW doesn't like part of a system to be replaced when an ENTIRE system can be replaced.)

How funny..,

Welcome to "grease monkey"/"shade-tree" 101..!!

Rule of tumb..,  "all systems operate in failure mode"

The good news is.., if the alt. needs to come out for testing.., it's way easier to remove than that of a VW...