HELP,,electrical nightmare 90YJ 2.5

when i hook up to the back post on the alternator, and then to ground, the numbers are all over the chart, up and down all the way up to 35, and down to 4

gawd, im going crazy,

johnp

The only thing you can measure to ground is voltage - and my voltmeter better not beep at me there - it would drive me nuts. Ohm meter is a different story - there the beep helps but that function is useless with voltage on. Measure voltage from ground to each point or between the two end of the connection.

While a fuse wire that blows due to over current will usually go in the middle of the link and creat a clean, well defined break, one that breaks at a crimp often gets confusing. What happens is that some of the wires break due to mechanical stress (or get cut by the crimper) and the smaller number of strands that finally blow don't melt the whole wire - the 'whiskers' will make intermittent contact and the heat will actually cause them to move rather than melt. If you have continuity in the wire, the voltage at the battery is identical to the voltage at the alternator output stud (less a few millivolts if the alternator is charging hard). If the alternator output voltage is above the battery voltage you have a connection problem - period. If the alternator is working, it should increase the voltage when you start the engine. If it doesn't, you either have a bad ouput lead (fuse links, etc.), a bum alternator OR the rotor current is not getting there. The small plug (in anything but the Delco single wire systems) supplies an enabling current. If that is absent, the alternator will put out some voltage when running but won't have enough excitation current to provide charging power. I don't recall a fuse in the control leads but check the see that all the leads to the alternator are good.

Whats the "technical" term for the relay on the firewall, (where my batt/starter fusable links bolt to.) or a part number,

shucks didnt have it in there computer or any of there books,,,awww-schucks,,,,

im going to Napa today to get fusable links and the relay to replace mine,

from what your all telling me its in there, so frig it,,, its all getting replaced.

MIKE, BILL, WILL, a BIG thank you for all your help here,

johnp

You have a very bad connection between the battery positive post and the alternator positive post. That 0.1V drop is 'huge' when it comes to power loss and the alternator could be going insane trying to bridge the bad connection.

99% of the time that bad connection is at the starter relay as your volt drop readings indicate.

You still have a 'real' alternator in there, so the PCM isn't an issue.

First you need to clean the connections, then try the volt reading when running again and everything plugged in properly.

When my starter relay connection gets punky, my volts start climbing high before taking a dive when it gets too bad for the alternator to bypass.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Man you just have one freaking dirty connection on the relay post. Take the wires off and clean them!

They call the thing the starter solenoid relay, but it's just dirty or the engine wouldn't start. A new one will not help because the wire loop connection is still dirty.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Dirty Ditch Dawg wrote:

Mike, this relay,,starter-relay, is this the relay on the firewall? sorry for my stupidity,

could i have fried this relay?

ive cleaned all connections,

im getting voltage from batt to alt on all tests, im getting voltage in my brown wire on the "two-wire" plug when the key is on, , so i figure ill change out that relay and my fusable links next,

i was going to try a new relay first, but schucks dont even know what it is, its not in there computer, or books,

then my fusable links,

unless theres a test for the relay??

electricaly challenged,,now with nightmares, maybe start drinking, sell the jeep, johnp

johnp

O.K. im gonna go clean it again, be back in 20.

johnp

You have to nail the volt drop down and get rid of it.

I start at the battery posts with my volt meter. I will use your numbers.

Post to post reads 12.7V

From the negative post to the positive clamp 'must' read 12.7V.

From the negative post to the starter relay post 'must' read 12.7 or there is a bad connection.

From the negative post to the alternator positive 'must' read 12.7V.

So you have 12.7 as far as the relay 'post'. That means that connection to the battery is fine.

You then read 12.6 at the alternator post. Trouble.

The trouble is from the relay post to the alternator post.

If the connections are spotless, then the fuse link wire has issues. It can blow and partially connect still.

I have some small cables with alligator clips on the ends I use for jumping things to test them. Something like that could be used to jump from the relay post to the alternator post to see if the volts stabilize

Before you get into that stuff, please give us the volt readings with things clean and everything plugged in.

I compare battery post to battery post reading to the alternator post and alternator case volt reading. They must be exactly the same.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Dirty Ditch Dawg wrote:

Mike, re-cleaned all connectons, wire-brush, electrical cleaner, sandpaper, electrical cleaner, whiped with rag, reconnected all wires, to relay and alt,

re-tested, with volt-meter,

Batt engin off,

12.49V

-Batt-to-Relay,12.49V

-Batt-to-post on back of Alt,12.49V

Running at idle speed,

Batt 12.25V

-Batt-to-Relay,12.24V

-Batt-to post on back of Alt,12.24

johnp

Mike, engine off,

12.54V batt neg to pos 12.54V batt neg to relay 12.54V batt neg to alt post 12.32V alt post to alt case

GRRRRRRRRRRR

johnp

Ok, the alternator is not turning on.

The small brown wire should have 10-14 volts on it when the engine is running or when the key is in the 'on' position. This wire should/could be lower volts than the direct power line so no worries, but it must have 10 volts at least.

I think you said it had power right?

If so, take a hammer and give the alternator case a whack while it is running. (stuck brushes syndrome)

If that doesn't bring it up to 14V+, shut it off and see if you can hand slip the alternator pulley in the belt. If it slips, the alternator won't turn on likely, so tighten or replace it if already tight.

The other 'real' sneaky one is the small white plug on the back of the alternator...

The pricks changed the order of the pins right around 1990. So the brown and red wires could just be in the wrong place. Seriously.

They can be removed from the plug with a small screw driver by pushing down on the clip on the back of the brass piece from the front side and pulling from the wire side of the plug. You then might have to bend the clip back up to hold good again.

Check that out and get back to us please.

Mike

Dirty Ditch Dawg wrote:

That says the ground is also dirty.

Try from alternator case to battery positive and walk it back until it comes up the same. Meter pin on the case, the bracket, the block, the bolt, the black ground wire, the battery.

Mike

Dirty Ditch Dawg wrote:

Engine running, alt-post to alt case, 1.1V alt-post to jeep frame 12.2

johnp

Alternator is not turning on. See my other post.

Mike

Dirty Ditch Dawg wrote:

I just checked on mine and the brown wire goes to pin #1 on the alternator case.

Mike

Mike Roma>

Ok, the alternator is not turning on.

The small brown wire should have 10-14 volts on it when the engine is running or when the key is in the 'on' position. This wire should/could be lower volts than the direct power line so no worries, but it must have 10 volts at least.

Mike, brown wire has 11.85V key on enginge running, 11.64-11.71V

alt to batt-12.21V

I think you said it had power right?

If so, take a hammer and give the alternator case a whack while it is running. (stuck brushes syndrome)

Mike, whacked it 5 times 4 for you 1 good one for me....grin,,,

12.21V,,grrrrr, alt to batt,,

If that doesn't bring it up to 14V+, shut it off and see if you can hand slip the alternator pulley in the belt. If it slips, the alternator won't turn on likely, so tighten or replace it if already tight.

tried your "slip-test," its tight.

The other 'real' sneaky one is the small white plug on the back of the alternator...

The pricks changed the order of the pins right around 1990. So the brown and red wires could just be in the wrong place. Seriously.

They can be removed from the plug with a small screw driver by pushing down on the clip on the back of the brass piece from the front side and

pulling from the wire side of the plug. You then might have to bend the clip back up to hold good again.

Check that out and get back to us please.

original wireing,,,

12.9V atl-to-batt 12.10V atl-to- ground frame 1.2V alt-to-case

wires reveresed, Alt-to batt 12.21V alt-to-ground frame 12.18V alt-to-case .6V

johnP again thanks for helpng me out here,

Mike

Your readings should have it running.

The alternator is no damn good.

One last test just for the heck of it....

Try running a booster cable from the battery negative to the alternator case and see if it turns on.

I have seen that happen twice.

Mike

Dirty Ditch Dawg wrote:

WHOOOOOOWHOOOOOO,, i think,

Mike writes,,,,,,,One last test just for the heck of it....

Try running a booster cable from the battery negative to the alternator

case and see if it turns on.

I have seen that happen twice.

Mike make it three times, hooked cable to neg on batt. reached over and clipped the alt bracket, BIG spark, jumped, re-clipped the cable no spark, alt-post to ground 14.5 volts my batt is charging acording to my dash gauge.

SO NOW,,, whats the BAD,,good,,news? i havnt shut the jeep off yet,

johnp