Working through some electrical issues in the WB140, turn the key, get the normal lights, can hear the lift pump ticking, but won’t attempt to turn over. Can jump the starter solenoid, starts just fine. The starter / safety relay has 3 inputs - 12V from the fuel pump circuit, measure 12.3V when key is in the start & run position - 12V from the key switch, which passes through the neutral relay, have 12.3V on this pin when key is turned, direction control in neutral, 0V when not in neutral - An input that goes to the alternator and tachometer, measures 0.1V when trying to start. I can tie all 3 inputs to the start / safety relay to 12V, unit cranks just fine. So I suspect the 0.1V from the alternator is my problem. Unit has a Hitachi 4-wire alternator, 1 pin plus the output goes to the battery, one input goes to the fuel pump 12V circuit through a 100- ohm resistor and there is the wire leaving the alternator that goes to the safety relay & tachometer. Does anyone have any info on this alternator and what the separate wire leaving the alternator does? Next step is to check the 100-ohm resistor (no idea where it is) and verify there is 12V on the resistor.
Is the relay youre talking about located in a big black box under hood near the firewall. If so should be a marked Hitachi AST1-26. There are a lot of electronics inside and I suspect that is your problem area. Sometimes they can work intermittently, are you seeing this? The relay is very hard to find and they are quite pricey when you do. There is a simple work around
Thank you! You may well be on point here, I know the alternator tachometer output is functioning since the tachometer works. Was going to unplug the 2-pin alternator connector and see if it measures 100 ohms between pins. Yes, the relay is in the black box on the fire wall, has the part number you mentioned. Can you point me to the work around?
One more question. Komatsu has made identifying this part a challenge. In the schematic it’s called a “safety relay”, in the legend table for the schematic it’s called the “starter relay”, and in the parts book (page E-40) what appears to be the relay in question is called “Relay, Preheat”, with no mention of either a safety or starter relay. As you mentioned, the Hitachi part number is on the part, I was searching for the Komatsu number as that might open up more supplies. The part in question carries a Yanmar part number YM129136-77200, it’s available & pricy, but don’t want to buy if it’s the wrong part.
I think your problem with them calling it preheat relay is that is a different part that is in that electrical box. In my service and parts manual it does not even show the safety start relay. That is because it is covered in the engine manual (yammar book) not the backhoe manual. You are correct on the part number though. Maybe your manual is different than mine.
I had sent a earlier reply on the work around that I used, but for some reason I don’t see it here. Strange You sound like you know you’re way around electrical so tracing the wires out shouldn’t be that bad. The way I fixed mine was to get a start solenoid like the ones Ford used back in 60’s/70’s. I used a 200 amp just because most are made in China and figured I was getting larger contacts maybe it would hold up long term compared to a standard 30-50 amp unit. Was only a couple bucks extra Wire from start switch to input of new solenoid, heavy wire going to starter solenoid to the output. Trigger wire from starter solenoid to the new solenoid. I also added a ground wire to the new solenoid just to make sure. There were a couple wires coming out of box that I just sealed up. All functions are still the same on the backhoe, but that wire from the alternator is no longer used. It’s only purpose was to keep you from starting the backhoe if it was already running. Sorry I’m not that stupid.
Last post on this topic. Cut the W/B wire (keyed 12V) on the module cable, spliced it to the R/ W wire on the relay. Cut the black wire on the module cable, spliced it to the G/W wire on the relay. Reinstalled, unit starts normally. Still have the must be in neutral to start protection, no longer have protection against trying to start when engine is running. Did I loose anything else? Found the OEM replacement for $310.05 plus shipping on line. Now to try and figure out why there is no temperature reading. Already fixed the won’t go into gear sometimes (bad gear relay)
Missed your reply, was out crawling on the machine. I kept the old relay since it seemed to work, though it looks like there are multiple options on eBay, plus our local NAPA probably has one. Thanks for the clues, this machine has been collecting flaky electrical problems, got tired of not being able to trust it. BTW - the machine uses a common Panasonic relay on the control board for transmission controls, they were like $3.50 from DigiKey, I replaced all of them when I had the board out. They are soldered in, wasn’t bad if you have the tools - hate to think what Komatsu would charge for a new board.
Funny I replaced all the relays on my board too. I thought that was the problem with my safety start relay, but after it didn't resolve I moved on. My unit had a ton of electrical issues when I got it. It sat outside all the time and I believe that was the source of most issues. Mechanically it was a cream puff, only 2100 hrs. Once I got all the electrical issues sorted out it has been a dream