I have been a reader of MUD for many year. The information on here helped immensely with my restoration of my 40. This is my first time posting…. Hope I’m posting in the right area.
I have a new to me 1991 LJ78 with an electrical problem. I’m getting intermittent power to the dash and the truck is running choppy with a voltage change.
I was having starting problems in the cold, so I ordered a new set of glow plugs. When the glow plugs got here, I put them in along with performing a compression test, all four cylinders read around 420-430. I tested all four of the old glow plugs and they were all operational. I left the new glow plugs in. Using the Wilson switch that the previous owner had installed I tried to start it up and it acted like the glow plugs weren’t working.
The bus bar was installed correctly. No grounding out to the motor. Tested the Busbar with a multimeter with the Wilson switch engage. I was getting 12 V to the glow plugs. Attached is a picture of a plug that was disconnected when I purchased the vehicle. I believe it’s for the glow plug timer. I plugged this plug in and tried to start it with the Wilson switch and watch my voltage gauge go from 14v to 0 . I then proceeded to pull the glow plugs to find out that the person I ordered from on eBay sent 19 V glow plugs instead of 11 V.
I put the old glow plugs back in, cleaned up the busbar and it started up, but had fluctuation to the voltage gauge on the dash. I checked the terminals to make sure they were tight and noticed that the negative terminal soldering had come lose. I am assuming from some sort of spike that the terminal got hot enough to melt the solder. I resoldered the terminal, put heat shrink on it and cleaned up all the other ground that I could find. these included ground from negative terminal to motor, negative terminal to radiator support, both fenders, and the ground from the frame to the motor. I checked the continuity in the ground cable from the terminal to the motor and it read zero.
I then ordered a new set of factor Toyota fusible links thinking that might be the problem but it’s wasn’t I still had voltage spikes.
Over night i completely lost power. I could turn the key and would get power to Acc but nothing in ignition or start position. Almost like the batter was dead. The voltage on the batter is 12.7 and it has been load tested.
At the bottom of the steering column where the ignition switch plugs into the wiring harness I get 11.5 volts to the white and white/red wires. With the key in the ignition the door light on the dash would come on and it would beep at you if the door was left open. The voltage at the key switch is 11v. With the key in Acc position I get 10.5v to the backside of the key switch. The radio and clock will work. When I turned the key switch to the ignition position I would lose all power. When I turned the key switch to the start position I still had no power.
Today for some reason I got power back to the key switch and was able to get it to start. Glow plug worked and it fired right up but still runs choppy with the fluctuations of voltage on the dash gauge. The voltage at the back of the key switch was checked with the multimeter and matches the voltage on the dash. While running the battery voltage gauge on the dash will fluctuate between 0 V to normal operating range of around 14 to 15 V. When the voltage reads zero on the dash the temp gauge will spike and the fuel gauge goes to zero. The clock and radio will stop working as well. If you turn on the heater the dash gauge will drop to zero. The headlights will not turn on.
At the battery with a multimeter the voltage between the positive and negative terminal is reading 14.3 V. When the dash voltage drops to zero, the voltage at the batter will drop to 14.1.
If you try to drive the vehicle, it cuts out and putters. If you give it gas, it will hesitate on you like it’s not getting fuel.
Today while was running, I could hear a relay clicking on and off underneath of the dash. I looked at the wiring diagram and can’t find anything underneath of the dash for relays that would cause the symptoms I’m getting.
With my limited electrical knowledge, I checked relays on the left fender and they seem to be working fine.
I’ve checked the ECU to make sure that it didn’t backfeed and burn anything out. All the plugs going into the ecu look good. I pulled the panel off and the inside of the ECU looks all right nothing burned.
I checked the continuity of the white and white and red wire, running from the positive terminal to the base of the ignition switch and they read zero. I don’t believe there’s a short on that line.
During the course of events the engine fuse and charge fuse has blown. They were both replace. All other fuses have been checked. The glow timer fuse terminal has been completely removed by previous owner or someone in Japan.
Thank you in advance. I’m at a loss of things to check for.
My only thought is it could be a relay or ignition switch that I didn’t electrically check properly, but I don’t want to start throwing parts at it and not resolve the problem.
