87 Bronco 2 electrical help needed.

[jose87bronco11]

I recently bought an 87 Bronco 2. His sons accidently hooked up the battery backwards twice. I replaced some wires and did get it started but it does not hold a charge. One wire goin from the Starter solenoid to Alternator was completely burned. Long story short I have tried almost everything to try to get it hold a charge. So I disconnected the wiring harness from the Alternator and battery has not gone down. Oh i did have the Alternator tested and it tested good so what in the world is goin on need help.

 

[RonD]

Welcome to TRS

1987 was the last year for the AMP gauge on the dash, so it has a different wiring setup that later years
But it could be either way, an AMP gauge(+ and -) or a Voltage gauge with numbers on the dash
Which do you have?

The AMP gauge wires were in that larger wire you replaced that ran from B+(back of alternator, a stud nut terminal) to the starter solenoids Battery positive terminal(post)

You don't need them but you DO NOT want to hook them up without the Shunt, which would have been destroyed if the larger wire was
AMP gauge used a Red/orange wire and a Yellow green wire, leave them disconnected, for now


Its easy to test charging system
Test battery voltage first, remember it
Key OFF
Use alternators metal case as the Ground for volt meter
Test voltage on B+, should be battery voltage, exactly
If not new wire is bad, this wire NEEDS to have a fusible link to continue to work

Unplug 3 wire connector on the back of alternator
Test Yellow wire, should be Battery voltage
If not its disconnected or burned out

Test green wire, should be 0volts
Turn key ON, engine off
Re-test green wire, should now see battery volts
If not then ignition switch may be damaged
Green wire is the ON/OFF switch for alternator, no 12v here with key on means no charge, 12v all the time means drained battery

Check that White jumper wire is plugged into its single spade terminal and not frayed

And that's it, truck system is tested once those 3 voltages are reading correctly

Start engine
test battery volts, should be 14.1 to 14.8volts, if lower than 13volts, alternator is bad, no maybe

Can't test alternator at auto parts store, just FYI, you can test alternator in a vehicle by doing the above wiring tests
If the 3 wires are OK and alternator doesn't raise voltage above 13.5volt with engine running then its bad, period
Its not that complicated of a system

 

[jose87bronco11]

Thanks Ron I did replace the Ignition switch it was coming apart not burned. I did replace all of the Fusible links and Diodes from a donor 87 Bronco 11 at our local wrecking yard and and the Alternator wiring harness no stud nut on Alternator just push in terminals . How can i check those fusible links and diodes? I heard that the alternator has an internal diode if it does would alternator still test good if it was burned out?

 

[Curious Hound]

Hooking up the battery backwards should not burn up diodes. Diodes are devices that allow current to flow in only one direction. So, checking with a meter on the ohms scale, should read 0 ohms in one direction and infinite ohms (some digital meters read overload or OL to represent this an analog meter will read at the maximum end of the scale) when you switch the leads to read the other direction.

A fusible link should read 0 ohms if good. It is just a piece of wire that is a specific size so that it melts apart when too much current passes through. It's just a fuse that looks different from other fuses.

The alternator has 6 diodes in it's rectifier, if I recall correctly. Probably didn't hurt that. But you could try a new rectifier.

The ecu is probably the most sensitive item when it comes to reversing polarity in the sysyem.

 

[RonD]

Testing the 3 wires does it all, do those tests
No guessing needed

If wires are good then alternator is bad, assuming no charging

 

[jose87bronco11]

Hooking up the battery backwards should not burn up diodes. Diodes are devices that allow current to flow in only one direction. So, checking with a meter on the ohms scale, should read 0 ohms in one direction and infinite ohms (some digital meters read overload or OL to represent this an analog meter will read at the maximum end of the scale) when you switch the leads to read the other direction.

A fusible link should read 0 ohms if good. It is just a piece of wire that is a specific size so that it melts apart when too much current passes through. It's just a fuse that looks different from other fuses.

The alternator has 6 diodes in it's rectifier, if I recall correctly. Probably didn't hurt that. But you could try a new rectifier.

The ecu is probably the most sensitive item when it comes to reversing polarity in the sysyem.

Thanks Eric where is the ecu located on my 87 Bronco 11.

 

[jose87bronco11]

Welcome to TRS

1987 was the last year for the AMP gauge on the dash, so it has a different wiring setup that later years
But it could be either way, an AMP gauge(+ and -) or a Voltage gauge with numbers on the dash
Which do you have?

The AMP gauge wires were in that larger wire you replaced that ran from B+(back of alternator, a stud nut terminal) to the starter solenoids Battery positive terminal(post)

You don't need them but you DO NOT want to hook them up without the Shunt, which would have been destroyed if the larger wire was
AMP gauge used a Red/orange wire and a Yellow green wire, leave them disconnected, for now


Its easy to test charging system
Test battery voltage first, remember it
Key OFF
Use alternators metal case as the Ground for volt meter
Test voltage on B+, should be battery voltage, exactly
If not new wire is bad, this wire NEEDS to have a fusible link to continue to work

Unplug 3 wire connector on the back of alternator
Test Yellow wire, should be Battery voltage
If not its disconnected or burned out

Test green wire, should be 0volts
Turn key ON, engine off
Re-test green wire, should now see battery volts
If not then ignition switch may be damaged
Green wire is the ON/OFF switch for alternator, no 12v here with key on means no charge, 12v all the time means drained battery

Check that White jumper wire is plugged into its single spade terminal and not frayed

And that's it, truck system is tested once those 3 voltages are reading correctly

Start engine
test battery volts, should be 14.1 to 14.8volts, if lower than 13volts, alternator is bad, no maybe

Can't test alternator at auto parts store, just FYI, you can test alternator in a vehicle by doing the above wiring tests
If the 3 wires are OK and alternator doesn't raise voltage above 13.5volt with engine running then its bad, period
Its not that complicated of a system

My Bronco 2 has this dash cluster

 

[RonD]

No AMP gauge so no Shunt, which is good, probably just has a Charge light(Battery light) as an indicator

When you turn on the key(engine off) do you see that light, usually its Red and it will stay on when other lights go off after 2 seconds or so(thats a bulb test)

Pull the wire off the B+ terminal and test if wire has full battery voltage, if not then wire is bad or fusible link
This wire should be a direct connection to battery positive, with fuse/fusible link at battery end of the wire

 

[jose87bronco11]

No AMP gauge so no Shunt, which is good, probably just has a Charge light(Battery light) as an indicator

When you turn on the key(engine off) do you see that light, usually its Red and it will stay on when other lights go off after 2 seconds or so(thats a bulb test)

Yes it is red stays on reads battery once it went of after a few seconds later it just stayed on after i started the Bronco.

Good I have been scratching my head trying to figure out what a Shunt is or looks like.

 

[RonD]

A shunt is just a slightly smaller gauge wire between Alternator's B+ and Battery positive
An AMP meters 2 wires are hooked up to each end of the shunt wire

So "some"(like 5%-10%) of the alternators AMPs will pass thru the AMP meter on its way to the battery

The gauge and length of the Shunt wire is matched for the AMP meter so it can give an accurate reading if it has numbers
Some just have a +(charge) and -(discharge) so not specific, so shunt gauge and length is not calibrated, just needs to be a slightly smaller gauge so some of the AMPs will pass thru the gauge

Think of a 2" water pipe that has a short section of 1.5" pipe with added 1/2" pipe connect to and running next to the 1.5" pipe
Most of the water passes thru the 1.5" pipe but some will also flow thru the 1/2" pipe because of the restriction going from 2" to 1.5"

That's a shunt

 

[jose87bronco11]

Welcome to TRS

1987 was the last year for the AMP gauge on the dash, so it has a different wiring setup that later years
But it could be either way, an AMP gauge(+ and -) or a Voltage gauge with numbers on the dash
Which do you have?

The AMP gauge wires were in that larger wire you replaced that ran from B+(back of alternator, a stud nut terminal) to the starter solenoids Battery positive terminal(post)

You don't need them but you DO NOT want to hook them up without the Shunt, which would have been destroyed if the larger wire was
AMP gauge used a Red/orange wire and a Yellow green wire, leave them disconnected, for now


Its easy to test charging system
Test battery voltage first, remember it
Key OFF
Use alternators metal case as the Ground for volt meter
Test voltage on B+, should be battery voltage, exactly
If not new wire is bad, this wire NEEDS to have a fusible link to continue to work

Unplug 3 wire connector on the back of alternator
Test Yellow wire, should be Battery voltage
If not its disconnected or burned out

Test green wire, should be 0volts
Turn key ON, engine off
Re-test green wire, should now see battery volts
If not then ignition switch may be damaged
Green wire is the ON/OFF switch for alternator, no 12v here with key on means no charge, 12v all the time means drained battery

Check that White jumper wire is plugged into its single spade terminal and not frayed

And that's it, truck system is tested once those 3 voltages are reading correctly

Start engine
test battery volts, should be 14.1 to 14.8volts, if lower than 13volts, alternator is bad, no maybe

Can't test alternator at auto parts store, just FYI, you can test alternator in a vehicle by doing the above wiring tests
If the 3 wires are OK and alternator doesn't raise voltage above 13.5volt with engine running then its bad, period
Its not that complicated of a system

Ron here are the test results

test 1 = 13.04
test 2 = 13.03
test 3 = 10.05

test when engine running = 18.66

I did replace Ignition Switch with new one last week

 

[RonD]

You will blow up the battery sending it 18.66volts!!!!!!!

Most it should ever see from alternator is 14.9 volts, never over 15volts

So what was battery voltage key OFF?

 

[jose87bronco11]

You will blow up the battery sending it 18.66volts!!!!!!!

Most it should ever see from alternator is 14.9 volts, never over 15volts

So what was battery voltage key OFF?

13.04

 

[jose87bronco11]

Test # 3 on green wire with key on was 10.05 is that to low?

 

[RonD]

Yes, should be no lower than 12.8v with key on, if battery was 13v

But alternator is bad in any case, well voltage regulator inside it is, if it outputs more than 15volts running