[MRogers]

Anyone know a way to test the black box on a 91 non-intercooled 5 speed truck? box is (attached to the firewall under the brake booster)

I have a no-start problem and I've checked most of the obvious stuff: fusible links, ign switch, neutral and clutch safety switches.

If I pull the plug off the mystery black box and jump the yellow wire (#1 top left on 6 pin plug) the engine will run and start normally. I have to disconnect the wire to shut the engine off because jumping it directly to 12v energizes the fuel solenoid.

I'm working with the wiring diagram in the 1991 Chrysler motors "service manual supplement - diesel engine". It doesn't go very deep into advanced troubleshooting and I'm trying to figure out exactly what this mystery box controls/how it works. I think it has something to do with controlling the intake heater grids, but this wiring diagram is a mess.

Thanks in advance for any wisdom on the subject.

 

[huntinguy]

Could you get us a picture of this box?

 

[cumminssmokeman]

your ignition switch could be the problem??

*woops never mind you checked that??

are you getting power to fuel selinoid without jumping yellow wire??

 

[jimbo486]

i believe it is known as the "brain box" for the grid heater system.

 

[MRogers]

i believe it is known as the "brain box" for the grid heater system.

Problem is that there's no troubleshooting chart for what power wires going in are controlling which power wires coming out.

I know there was a wiring schematic somebody drew up for an intake heater grid bypass lurking somewhere on the net (converted everything to manual operation) but I can't find it.

I would really like to simplify my wiring and get rid of this box if possible. I live in GA so the intake grid heater isn't necessary very often.