Hi I am new to both this site and as being an owner to a Mini Excavator. I bought this 2004 Cat 303 CR in the spring and it has 1400 hrs on it. The previous owner has bypassed the glow plugs and fuel shutoff and installed two toggle switches to them. I would like to put these back to original. After checking the factory wires to them I have found that there is no power thru them? I have replaced both glow plug relays, both timers and Ignition switch. I am trying to find the wiring schematic so i can trace the wiring without me having to cut into the protective sheeting around the wiring harness. My next move is to check the wiring with my omh meter to see if i have conductivity thru them. Anyone run across this issue or can give me hints on what to do next. Also anyone have an idea where i can come up with the wiring schematic. I can purchase it thru Cat but the want $75. Any help anyone can give me will be greatly appreciated.
A Serial Number for the machine would be a good start. From there I'm sure we can come up with an electrical schematic for much less than $75.
reply Hi Nige The serial number is DMA 02631. It does not have a cab it is open canopy. This problem is not affecting the operation of the machine i am afraid if the toggle switch for the glow plugs is accidentally hit and left on it could result it more damage then i would like. Besides this is becoming an obsession to me to find the cause of this problem. Thank you for your assistance.
Thanks for the S/N. A trawl around the system is in order......
View attachment 303 ign upgrade.pdf View attachment 303 RENR5576RENR5576-02_SIS.pdf Hi looking at the sch I would check the white wire # L987 as it is common to the ignition switch ,glow plug timer ,glow plug relay and engine shut down timer Also there is an ignition switch up grade with some wiring changes. yours may or may not have had this change I have included a copy of electrical schematic and the up grade doc. Mark
Hi Mark250 thank you for the schematic. I got the glow plug problem resolved it was that white wire L987, it was on the start side of the key switch so it was only getting power in the start position. I changed it to the relay position on the key switch and i am getting power back to the plugs and they are shutting off after approx 8 seconds. I have to check and see why i am not getting glow plug indicator light to come on. It maybe as simple as a bulb need to check wiring to cluster gauges. Now i am chasing the fuel shut off problem, have power to timer and have power from key switch but know power at timer from start (green wire). Not sure if relay is working properly. I am going to switch with one of the other relays to see if that it. Again thank you and i will keep you posted on my progress.
If your particular machine has not had the ignition switch upgrade it might well be worth your while to do it while sorting out the other electrical issues. It is maybe $60-70 in parts. The new setup only became standard from machine S/N DMA03509 and upwards.
Morning Nige So as you see from my post to Mark 250 I think i solved my glow plug issue. I still have the issue with the fuel shut off. Last night putting everything back together I checked the shut off timer and noticed that i do not have power to the green wire #306 which the schematic says is from st (key). I am assuming that it is from key switch start position. Since i moved white wire #L987 to relay position, has that some how affected that green wire? Also I noticed that the 10 gauge white wire at the start relay has no power i replaced relay still nothing? Traced that wire to starter and it is disconnected at starter? It looks like the prior owner has ran a new wire from key switch to starter sol.? Not sure if he did this to bypass the disable start relay which affected the start relay which also affected the timer? I see in the switch upgrade that there is two white wires at the key switch and that it is running to a different switch along with the purple wire from the relay side of the key switch. Do you think if I do the upgrade it might resolve my fuel shut off problem?
I was more thinking about doing the upgrade for reliability reasons, which is why it was introduced in the first place. Personally I would fix all the problems first and then think about doing the upgrade. Unless you do one thing at a time you can end up seriously confused, well at least I can .... Rather than chasing power you might be better using a digital multimeter and checking the resistance between one end of a particular wire and the other end. Pay special attention to any connectors that the wire goes through, because a connector with dirt/corrosion on the pins can be a prime source of a break in a circuit. I would actually suggest that if there are any connectors in the particular circuit you're looking at I would disconnect them as a first step and start checking resistance in each separate section of the circuit.
Morning Nige I took your advice and after several hour of checking wires and connections I still had nothing. I quit for a couple of hrs then went back to the schematics (which is prior to Ignition upgrade). And something was telling me to check the upgrade paper work that has the wiring diagram to the key switch. I went out to the machine and checked the wiring and found that the prior owner had wired the new upgraded key switch the way the old switch was wired. I rewired the switch according to the new upgrade and everything is resolved. I had to change the wiring at the switch a little because i do not have the second switch that Cat has wired into the upgrade ($98 for that one switch). I will look into getting that new switch, but am not sure why they installed that new switch (it is more or less a relay). Thank you for your help.
Morning Mark250 I did resolve all my issues. By sending me the Schematic and the Ignition upgrade paper it help me alot. More so the upgrade paper. You can see from my reply back to Nige what I ended up doing. Again Thank You.
I have a similar issue. The engine will not shut off when the key is turned off. I'm trying to understand what powers the Pink wire that attaches to the Engine Shutdown Solenoid? Quick review of what I've done to troubleshoot. I removed the seat to access the solenoid, and discovered the pink wire was disconnected from the shutoff solenoid. I reconnected it to the solenoid and started the engine, and when I turned the key off, it still would not shut down the engine. I disconnected the fuel line at the filter to shut down the engine. I tested the pink wire with the switch on/off and there is not voltage, which led me to believe the power comes from another source. I reviewed the wiring diagram in this thread and I don't know how to determine if power is coming in from L21 or L22, or both. Any help would be appreciated. Can I take a jumper wire from the connection at the fuel shutoff solenoid and touch it to the positive on the battery to narrow down if the solenoid is functioning or has gone bad?
I think that you will find that L21 & L22 are not wires, they are wiring harnesses containing multiple wires. I can’t look at the schematic at the moment but my best suggestion to interpret it to find out where the power is coming from would be to start at the shutdown solenoid and work backwards. Also I would suggest that you have a good read of all the colour code tables, etc, that are included on the schematic that explain how to identify what wire does what, what is powered and when, etc, etc. It would be useful to indicate if your Serial Number is above or below DMA03509 so that we know if it had the modified ignition switch circuit ex-factory or not.
My serial number is BXT00633. Thanks for your advice. I was able to follow the circuit back on the diagram to the Engine Shutoff Timer. I’m trying to determine if positive power to the fuel shutoff solenoid shuts down the engine?
I've sent you a copy of the electrical schematic applicable to your Serial Number. The one above is not the correct one. If you start at the shutoff solenoid and follow 327 Pink backwards it takes you to the Shutoff Relay. This has batt+ on 107 Red and that relay is pulled in by a voltage on wire H809 Yellow coming from the shutdown timer. Try a couple of tests:- 1. With the engine running apply batt+ voltage to H809 at the shutoff relay. Does the engine shut down.? If it does you need to look further back at the timer, if it does not then something downstream is not right. 2. If the engine does not shut down applying voltage at H809 YL, try applying Batt+ to 327 PK at the shutoff solenoid. Does the engine stop now.?
Thank you! This is very helpful info!
Check your messages. More info there.
Thank you! I got the correct wiring diagram.
What is this cable with a pull ring? Engine shutoff?
Yup. Manual shutoff group. It's covered in the Operation & Maintenance Manual. Which begs the question, do you have an O&M Manual for your 303.? If not you really ought to get one, about $50 for a pdf download.
Thank you sir! I need to get an O&M for sure. Do you have a link?
Yes indeedy. Go to https://catpublications.com/ When the popup appears click on "Continue as guest" Put SEBU8021 in the box and click Search. If you select a paper or CD version there will be S&H added to the price shown. A pdf download costs what you see on the screen and is ready almost as soon as you've paid for it. If you want a Parts Manual search for SEBP4461. They are a bit more expensive though........
Thanks! Ordered an O&M manual. I fixed the issue by replacing the Engine Shutoff Solenoid. You were very helpful!