Electrical question after lots of reading

[Triumph215]

Excellent question about running vs not running
12.5 volts - Engine off, no lights
12.0 volts

[Triumph215]

12.5 volts Engine off, no lights
12.0 volts Engine off, lights on
13.25 to 14.00 Engine running at fast idle, no lights
13.75 to 14.00 Engine running at fast idle, lights on.
Looking at it here it does not look like much but it is like the Ghostbusters truck going down the road. Very cyclic.
Yes Motorcraft and Ford systems are new to me, I have been learning a whole lot over these past four weeks.



Still trying to get the hang of posting too.

[Dave Jeeper]

On any vehicle the alternator or generator and the voltage regulator provide the power to the vehicle. Pulsing of all circuits will be coming from this source of power, probably the voltage regulator which is probably a separate unit from the alternator or generator. It would pay to have the battery tested since a bad battery might cause the voltage regulator to malfunction.



Always check your grounds, make sure that they are cleaned and apply dielectric grease to keep them from corroding. The fused wires are one half of the circuit, the other half of the circuit returns to the battery via the grounds which use the body, the engine and the chasis as "wiring" (they do this to save on copper wire costs). Check the battery terminals for corrosion, protect from corrosion with high temperature grease or dielectric grease. Check the grounds for the dash wiring for corrosion and tight connection (use dielectric grease).



I don't know if your year FSJ has a starter relay. The 89 Grand Wagoneer routes almost all power through the relay and this can cause big problems if it is not conducting electricity properly.


Sometimes the older Jeep electrical connectors with multiple connections can suffer from 2 things: a loose connector and also the female side can have individual contacts that increase in diameter and don't make a good connection with the male contact. Again, check for corrosion. This applies to the instrument panel connector and power window/door lock connectors if you have them.


The last item to consider if you are missing multiple functions are the fusible links. Right after the battery connection or the starter relay connection where the small and mid size wires start diverging, the wires will have some shrink wrap about 1 to 2 inches long. Under the shrink wrap is a short section (about 1") of meltable wire. These are like a fuse and are designed to melt before the rest of your wiring harness burns. They are difficult to diagnose because they are designed for the short section of wire to melt without melting the insulation over the wire. If you check the wiring diagram for the fusible links you can see which circuits/functions are supplied by each link. If one link supplies most of the functions that are dead on your vehicle, it could well be the fusible link.


Good luck,


Dave

[Triumph215]

The battery appears to be brand new but I will have it tested since it is the only thing I have not evaluated simply because it looks new. It will be good to have the whole thing checked over with the proper equipment anyway. All ground cables are new and connections are good, losing almost nothing coming back to the battery.
About that Fusable link. I have exposed the wiring harness all the way to the back of the engine on the passenger side. There is no fusable link in there, is it closer to the wiring block where it passes through the firewall? This truck is fighting me tooth and nail so I hate to open things up further than I have to.

No electricity passing through Temp Gauge, PCB in good shape.
I took the face off Temp gauge and the coils inside were burned black. Open connection from the far side of the Radio silencer to the A post so 12 volts everywhere. I already know the oil pressure gauge is dead. Since the fuse block had a 20 amp fuse in there when I bought it I will assume the fuel gauge is not coming back to life once I have the correct current flowing. Ordered three new gauges from BJs. The CVR in these will still die open like the stock gauge correct? Maybe I should still add the solid state 5v regulator that dies closed. I already bought the parts

[tgreese]

... Maybe I should still add the solid state 5v regulator that dies closed. I already bought the parts

You've got it backwards. Closed is on, open is off.

If you lose the ground to the dash, the CVR will go closed, ie constant over-voltage to the gauges. This is bad.

The IC conversion (7805 or 7806) will go open if it fails or loses power. This is the behavior you want.

[tgreese]

The fusible links are in the engine compartment. A '77 only has one, between the battery and the Jeep. Connection to the battery is at the starter solenoid, where the (+) battery cable from the battery connects. They just look like wire. Suggest you don't worry about them unless you lose power to the Jeep.

[Triumph215]

Got it done, all seems to work great. Put some gas in and the gauge moved, temp gauge working too. Now if I could find my electrical surge...

[Curly5759]

Have you tried disconnecting the alternator at the charge wire coming off the back and then running the engine? If the surge is gone, you know it is the alternator/regulator. If not, the problem lies elsewhere. Easy way to narrow the problem down.

[nograin]

If you're going to do ^that ^ make sure the wire's ring terminal does not touch any ground.

Another thing you (Triumph) can do is reconnect the ammeter. (Disconnect the battery when doing this). In addition, have a voltmeter handy. Since this pulsing is happening at idle, a multimeter will work fine. Between the two meters you will have a pretty complete picture of what is happening.