Hey Guys and Gals... Been wondering for quite some time and finally figured I would ask the professionals here. you see I've been aware of the starter safety relay function of not allowing the engine to start when the engine is running.....voltage seen from the alternator.... and how when the diode in the alternator goes bad it will also not allow the motor to start either due to thinking the engine is running.. My question is how exactly does this relay work??? Where does it get it's power to actuate the coil inside allowing voltage to flow to the starter motor solenoid? You see if the alternator is performing it's function and charging the system why in the world should we buy a new one just because of a diode.. ????? How can you bypass this relay without installing a toggle or push button switch... Sure do appreciate any info please.. i have a D65EX-12 that doesn't start until I put power to the solenoid.. I've checked the neutral safety switch for continuity and is working as it should. The only other thing I think is the alternator and that is why I asked about jumping the relay because the alternator is charging.. Darin
Could be dumb question but I believe there are two safety switches on Komatsu dozers. One for trans and one for hydraulics. My apologies in advance if you've already checked both.
Darin, The voltage that energizes the safety relay comes from the ignition side of the key switch thru the neutral safety switch. The safety relay coil has two control wires one from key switch the other comes from the alternator to the "R" terminal of the relay. If both sides have positive voltage (alternator producing) there is no ground so the coil does not energize. If however the alternator is not producing the "R" terminal provides the ground(thru the alternator) so the safety relay coil can energize and allow start signal to energize relay and bendix on the starter. As far as the diode, alternator has battery power to it so if the diode trio leaks voltage to the "R" terminal of the safety relay, the relay will be fooled into thinking the engine is running and starter will not engage.
So would it be safe to say that if I ground the "r" terminal then as long as theere is power from the key going through the neutral safety switch it should work then right? I am asking these things because I am trying to figure what is bad with the starting system and once figured I can then buy the correct part. Thanks so much for the help.
I would say that grounding the "R" would allow starter to engage, and allow you to troubleshoot. I have seen people just wire around the start safety relay more than once. Good Luck
Thanks again.
You should just be able to unhook it and if that's the problem then it should start
Ok so today I tried all we talked about but then checked for voltage from neutral safety switch and there is NONE. The key has power when turned to start but from the key black/white wire to the neutral safety switch there is no power.??????? I'm at a loss.. If I power (jumped voltage direct to the neutral safety switch it starts so that tells me the alternator is good.. Ran continuity through the neutral safety switch and it performs like it should so it is a feed from the key switch to the neutral safety switch. ??? Not sure where is would lose power unless it was corroded or eaten by.
The R terminal only has power when the alternator is producing voltage. The safety relay is normally closed. Voltage at the R terminal opens the safety relay and prevents voltage from the key switch to go to the starter solenoid. When the diode in the alternator goes bad the safety relay is open and the starter will not engage. The quick test of the alternator is to disconnect the R terminal and see if the engine will start. To bypass the relay, just unhook the wire from the key switch and connect it direct to the starter solenoid. Just remember that if you hit the starter with the engine running you will get lots of noise and bad things may happen.
THanks John.. Problem now is that I have no power through the wire from the key switch to the neutral safety switch.. Voltage at the keyswitch "c" terminal but somewhere through looms there is no power. At the neutral safety switch the wire color code goes from black/with white stripe to Black/ yellow strip then goes to power the safety relay on the starter. I was actually thinking about running wire spliced in the black/white AT the neautral safety switch so I wouldn't bypass anything and no damage can result from energizing the starter when the engine is running. I don't like to cobble things but trying to find this power loss is taking a toll on my pea brain.
About same issue but add main batt disconnect to menu I have D35E dozer (1995) with 25 amp alt--about same problem as darinray- Must ground a wire to start but also must ground same wire or my main batt disconnect relay will njot disengage. Loking at wiring dia, I was going to disconnect wire going to to terminal R on starter relay. No one had mentioned thye batt disconnect as part of same system. I must add ground to turn batt disconnect off after key is turned off. Does that change the dynamics of the conversation thus far.
Correction CORRECTION MY DOZER IS D37E5. also if I don't ground the Rwire, my key on red warning lights on dask stay on even with key off---that is until i ground the R wire??
Coalrulz and JohnC. Thank you very much. The knowledge and information that you are willing to give on this forum has helped me many times. This time you saved me from my machine catching on fire. I was clearing land and burning trees. The machine did right next to the burn pile and the wind was blowing embers towards machine and the machine wouldn’t start. I tried everything that I could think of with no luck. I went to this forum and did a search and y’all explained perfectly what my problem was and how to fix it. I was able to crank it up and move it away from the fire. Thanks again.
I disconnected the R wire and temporarily grounded it and the machine started. But if I permanently ground it the machine will start but it blows the control panel fuse. The wire is hot even though it’s disconnected from the R terminal on the alternator and it’s disconnected at the starter before the safety solenoid. Where else would this wire be getting power?