07 420E #KMW00766 Initial problem was the machine blew a fuel pump fuse and my operator realized if he held the key in the start position the machine would stay running. He cooked the starter I replaced it, I replaced the bad fuel pump (all Caterpillar parts). Rechecked and replaced blown fuses. When I start it now the starter continues to run as the engine is running, if you put it in gear the starter stops but will run again if you put it back in neutral. If I disconnect the starter relay with the engine running the starter stops if I turn the key off everything stops. I noticed if I disconnect the starter relay and turn the key to the start position the power to activated the starter relay stays energized. I tried a new key switch and no difference. I am pretty sure my guy cooked something by holding the key in start position for at least 5 to 10 minutes but I don't know what is before the relays. I also see no signs of any wires fried.
Time for A new relay.
forgot to mention I tried swapping out the relays
Are you absolutely certain that the wires on the starter and the key switch are where they are supposed to be ?
everything is exactly where it's supposed to be, I did find the power runs through the shift handle I will check that Monday
Did you try the placing the relay from the problem circuit to the functioning circuit to see if it worked ? Not all relays are rated for the same loads. If the relay isn't the problem it may take some meticulous wire tracing with a VOM to find where the power is coming from that causes the run on. I would begin on the start terminal on that new switch. Remove the wire that goes to the relay and check if there is a voltage on the switch / start terminal-- after turning the key to the start position and then releasing it to the run position. It is quite possible there is a short in the harness causing the continuous power to the relay. I once had one that had a open wire in the harness causing a no start situation. I simply ran a new wire along side the harness from the switch to the solenoid to fix it. I mention this because it may be one of the options solution for your problem.
The problem was a fuel lift pump suppressor (diode). The crank circuit activates the fuel pump relay after the machine was running the relay back fed the starter circuit. It was not easy to find the suppressor, I found 10 on the machine and they are all the same part number.
We are having the same problem where was the diode located I have been looking for hrs and can't find it..
Anyone else know where I can find this suppressor/diode for the fuel lift pump? Any help would be greatly appreciated
Heymcall has requested this post be deleted because it's the "wrong machine." Rather than deleting it altogether, I've just edited out the misinformation, so nobody wonders where heymccall's reply disappeared to.. Digger242j
Everyone has said it's the same bulb style diode as the rest of the ones in the machine they are about a half in round and 1 1/2" long we have found several just not the fuel pump one..
Below is an extract from the electrical schematic. There are 3 diodes of 106-8704 Part Number (10, 10A, & 10B) shown on the Platform Wiring but nowhere does it indicate which one performs which function. The only thing I can suggest is to attempt to identify the diode by the Wire Numbers (X977 Yellow & 307 Orange) that are connected to it.
I found the elusive diodes with the orange and yellow wire. Think of the hardest place to reach and you found it. It is right under the hydraulic tank. I removed the cab floor panel, there you can see it but reaching it, blindly reaching for it with only enough room for one arm, under the steering column and back under the hydraulic tank there is the (106-8704 fuel lift pump suppr diode) with the yellow and orange wires. I also did a continuity test on the yellow wire and confirmed it was the diode that ran to the lift pump relay.