Hey guys Happy New Year

I'm a new member here, been reading the forum for a while and really find it useful.

I've got a problem with the electrical system on my '91 F350 (diesel 7.3). It's been hard to start cold (needs glow plugs and return lines), and needs to crank for a while to start up. I got a little over-eager cranking it and something died. Now when I turn the key to the on position, the interior lights dim and the starter solenoid chatters.

I tried a few things but now I'm stuck:
I checked the starter relay, it has power to the main terminal and makes a definite clunk when I jumper the enable post with the 12v supply so it sounds OK.
I pulled the enable wire off the starter relay (on the passenger fender) and tried turning the key - lights dim, starter chatters, battery drops to 5 volts.
I took the output off the starter relay and turned the key - lights dim, starter chatters, battery drops to 5 volts.
I also used a remote starter switch to jumper it to the 12v supply and the starter solenoid clicked once on the first try then chattered on the 2nd and 3rd tries.

I can't figure out why the starter chatters when the starter is disconnected from the relay, unless it is fed from another switched source.

Does anyone have a wiring diagram for a '91 F350 (diesel 7.3 auto 4x2) or can point me in the right direction?

 

You could have burned out your starter. And if you everything was working properly before, you shouldn't need to switch around any wires.

 

Did you charge the batteries fully? That is step one. Otherwise pull that starter and have it tested.

 

What does the passenger side positive battery terminal look like?

What do the wires look like close to that terminal?

If the wire cover looks discolored or the wire insulation looks like it has swelled up or looks melted, my guess is you have internal corrosion inside the clamp/wire.

The other option is your batteries are not holding a charge or you have dirty connections.

The battery positive cable starts at the drivers side battery, continues to the passenger side battery.
Inside the passenger side positive clamp, three wires join.
Battery wire to starter.
Drivers side battery wire
Wire to the cab electrical systems.

Inside that clamp over time corrosion starts to form and blocks electrical flow.
As resistance increases, heat will be generated while the glow plugs are heating or the starter is cranking.

That is where the melted/discolored look comes from.

Also cranking the starter for more than 20 seconds without a 2 minute cool down time before cranking again is a very bad thing to do.

The starter will overheat, and then it is time for a replacement starter.

 

The chatter is due to not having enough juice available from the batteries.
If it was working before its simply dead batteries. Check and charge both.
This has happenned to me many times when I've had air intrusion issues.

Note that boosting from all but the biggest shop-size chargers or another large dual-battery vehicle won't help much. You have to load-test and charge both batteries disconnected from the truck.

If the truck has been hard starting keep in mind that it takes quite a bit of driving to re-charge two large batteries after each extended cranking start.

 

Thanks for the advice, the starter is definitely fried, I would've posted last week, just my computer went for a you-know-what.

Anyone else get snow? Old Rusty was parked out front and the plow buried her under. I dug it out enough to crawl under and check the starter, it's blown. Time for a new one. I think I'll take it to the garage for a swap, can't even see the top bolts

 

The top starter bolt is not really that hard to get to . I just changed out my starter in the driveway. You can always tell when you have a great truck when it leaves you broken in the driveway, HaHaHa. I used a standard depth socket, 6" extension and two 1" extensions. The 6" and the two 1" extensions allow you to get between the starter and the crossmember on the top bolt.

 

Nothing to be scared of when swapping starters. I did mine about a year ago, took me about 2 hours. Just take the top bolt out first and put it in last and you should be fine.