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electrical gremlins.... help

D

DaveVmax

NAXJA Forum User
Location
Georgetown, ON
Im having a problem with my 92 4L HO

ok so i start the truck up everything works no problem.... i go to turn the heat on/blower motor and the truck dies. I turn the key back then try to restart and i got nothing.. no radio, no blower motor, no fuel pump priming and no starter cranking.

now what could cause that issue? i let the truck sit for a bit and then i can start it up again and sometimes it will die then others it will stay running.

could there be a short in the blower motor? but would that short cause the whole truck to die?

if i turn the key all the way back towards me i still have radio every time.

now so you know this has been changed recently
blower motor - year old
fuel pump - 6months old
column - week old
ignition switch - week old
battery - week old
starter - week old

my guess is a short somewhere or a bad ground??? any ideas???
 
First step is always the same. Disassemble battery and ground connections. Polish them with scotchbrite or sandpaper, then clean with brake cleaner, spray start or electrical contact cleaner, then reassemble.
 
in my first post i said i replaced battery and ignition switch just recently myself i know i did it right and every connection were checked then checked again.... same with the battery.

but how could a short or bad ground in the blower motor cause the truck to die?? wouldnt that pop my fuse first?
 
I'm betting a bad ground somewhere - you're correct about the fuses, unless you have an extremely marginal connection somewhere. Check your head to firewall ground strap (replace with stronger one if needed), dipstick tube grounds, and any other grounds you can find.

When the truck dies, does the blower motor still work? It should, since that is only dependent on the ignition switch being functional, not on the engine management system.
 
DaveVmax said:
but how could a short or bad ground in the blower motor cause the truck to die?? wouldnt that pop my fuse first?
Click to expand...

Ideally yes but I don't know what's been done to it. Someone may have put a bigger fuse in or bypassed it entirely. I had one car that a shop replace a brown 14ga fusible link with a brown 12ga. There was a short in the defroster circuit and when the lady turned it on the harness smoked and engine died.
 
kastein said:
I'm betting a bad ground somewhere - you're correct about the fuses, unless you have an extremely marginal connection somewhere. Check your head to firewall ground strap (replace with stronger one if needed), dipstick tube grounds, and any other grounds you can find.

When the truck dies, does the blower motor still work? It should, since that is only dependent on the ignition switch being functional, not on the engine management system.
Click to expand...

when the truck dies the blower motor dies aswell.

its weird because i just literally changed the switch and it was doing something similar before the switch replacement.

so my guess is a bad ground.

does the fuse block have a main ground on it inside the cab?
 
ok i did a little more investigating.... i got the truck started again. while i was running i shook wires around and tapped the switches checked the plugs and nothing...it was still running.

so i switched the climate control switch over to the first ac setting and the truck dipped down in rpm then came up so i switched it right over to heat and boom dead.

switched it back to off and it would start again.... so something is going on with the blower motor. im just surprised that it would make the whole truck die like that....

The previous owner half assed a lot of the wiring in this truck so that doesnt help.
 
If you have a big enough load it will pull the voltage down. The blower still works in all settings (or it's suppose to). Sounds like something he did.
 
it works in all settings still.

looks ill have to track down some wires in the daylight.

any other tips or things for me to check that might be related?....does the blower motor have a relay?
 
The relay is used for high only. It just dawned on me that the wires behind the control head may be hitting the lever on the controls, cutting and shorting the wires as you move it.
 
Not sure in '92, but in 2000, the relay works for all speeds. But that is not the issue.

Wierd that it dies on heat and not on AC. AC should draw MORE current. I would check out the wires behind the control head like MJR says. Reach under and wiggle stuff behind there and see if it dies.
 
winterbeater said:
Not sure in '92, but in 2000, the relay works for all speeds. But that is not the issue.

Wierd that it dies on heat and not on AC. AC should draw MORE current. I would check out the wires behind the control head like MJR says. Reach under and wiggle stuff behind there and see if it dies.
Click to expand...

So it is and they switch the ground side through the resistor instead of the power side. Oh and there is no relay on the early models, my bad.
 
thanks Joe im gonna look into that.

but i was playign around with it today and noticed the truck runs perfect with the unit un pluged... but once i plug it in and switch it to any setting it shuts the truck off.... so i think ive narrowed it down...
 
You have a handle on it, but without upgrading the circuit any repair will be temporary as so much of that circuit is weak.

Heck, pick a circuit on the XJs and there are known problems! :explosion
 
Back to the top.... i figured out everything above but..

when i start the truck and put it into R N D etc... the truck dies then i put it back into P and it will start up no problem.


could this be a NSS?
 
DaveVmax said:
Back to the top.... i figured out everything above but..

when i start the truck and put it into R N D etc... the truck dies then i put it back into P and it will start up no problem.


could this be a NSS?
Click to expand...

Doubt it but anything weird can be possible. I'd say it's a wiring/ground connection when the engine/trans move. Try starting it in Park and moving the wiring harness around to see if it dies. I've seen the connector for the ignition coil do that (loose terminals).
 
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