retro

Good move.... you'll need to replace the china Regulator/rectifier too, before you plug in the used OEM CDI. When the charging voltage exceeds 16 volts the CDI may fry.... also if the charging voltage is mostly unrectified AC the CDI may fail. So the china regulator/rectifier is a potential bomb. Its not a matter of "if", but when with china knockoffs.... we see it all the time.

I hate it when I gotta be the bearer of bad news but you can't fix a Honda with china knockoffs. We can't help ya at all until all parts on your Foreman are genuine Honda. You can probably find good used parts on powersportsnation.com if you prefer used versus new.

Ahem.... it's a $150 prepaid Visa, 50 bucks more than ya thought! :) Might be enough to keep your lights on.

Wow, 33% more AH capacity with 20% higher CCA in the same plastic case!

Ok, the Blue/yellow wire resistance (the pulse generator) test is within spec. But the ignition coil primary windings resistance measured out of spec. The coil primary is supposed to measure between .1 & 1 ohms. Has the ignition coil been replaced? Is it an original Honda coil? Try this: Unplug both wires from the ignition coil (note the wire color/terminal location so you can plug them back in correctly) and disconnect the spark plug cable from the spark plug. Measure resistance between each wire terminal on the coil while probing with your other multimeter lead inside the end of the disconnected spark plug cable. Let me know what those two resistance measurements are.

You may as well remove the racks and both fenders because we'll likely be snooping around at both ends of the wiring harness. While you're tinkering you may as well remove the bolt that holds the grounds wires/cable down to the frame and shine up the steel around the bolt hole and shine up the wire & cable eyelet ends. You can use sandpaper, a stiff wire brush or whatever ya got handy to remove rust & corrosion. Once clean, bolt those ground wires back down to the frame. See the image for grounds bolt location. If you have a desktop computer, laptop or a tablet you can view a copy of the service manual for reference. https://drive.google.com/drive/folders/12hzs10L_Gwu0aVyp8vhmEXNdf2N2P7tk The title of the manual you need begins with: 5101394-Honda_TRX420_Rancher_420_[...]

Those might be the wiring harness junction connectors? See the component location image: Yeah, see the image above Yeah we are only looking for a short, either in a component, or in the wiring harness. So we're just tracing circuits out for now..... verifying that they're intact (no broken wires) and are not shorted. This is challenging and fun! I oughta be thanking you! :) Leave components unplugged unless I instruct otherwise. I gotta know where you're at... else we'll get out of sync and make mistakes. Those three inside the circle are harness junction connectors. They are used to connect common wiring together, such as ground wires, power wires, etc. The relay module has an 8p connector... 8 wires going into the connector plug.

Right, we're gonna find out where the short is now. You can purchase OEM parts later on if you wish. Ok, I am going to be providing instructions for troubleshooting in a step-by-step manner. After each instruction that I post here I will await your response before proceeding to the next step. We won't be jumping around or speculating on things, each step will be deliberately ordered and I'll provide images for your reference wherever possible. This diagnosis will take some time to complete, possibly days... tomorrow the 14th I will be unavailable for part of the day, but I'll be here at some point. Disconnect BOTH of the battery cables from the battery and leave them disconnected until/unless I ask you to reconnect them. 1st test -- With your multimeter in Continuity mode, probe the positive battery cable terminal eye (that is disconnected from the battery) and with the other multimeter probe touch BOTH of the Black/green wire terminals inside the Engine Stop Relay (NOT the fuel pump relay) connector. You should measure continuity on both terminals. Let me know those results. Then, with your multimeter in resistance mode, touch one multimeter probe to frame ground, then probe each Black/green wire terminal inside the Engine Stop Relay harness connector. You should measure resistance through one Black/green terminal but not the other. Let me know those results. Then unplug the PCM/ECM Gray connector. With your multimeter in Continuity mode, probe the positive battery cable terminal eye (that is disconnected from the battery) and with the other multimeter probe touch the Black/red wire terminal inside the disconnected PCM/ECM harness connector. You should measure continuity, let me know that result. Then, with your multimeter in resistance mode, touch one multimeter probe to frame ground and the other multimeter lead to the Black/red wire terminal inside the PCM/ECM gray harness connector. Let me know that result.

I've got to go outdoors and do my chores. I'll be back in a bit with instructions for the 1st test.

Using the dropdown buttons on this page (scroll down): https://www.rockymountainatvmc.com/oem-parts/Honda Select: All-Terrain Vehicle (ATV) Select: 2010 Select: TRX420TEA (10) All-Terrain Vehicle (ATV), USA VIN# 1HFTE344- A4300001 Then on the next page select from the dropdown list: Wiring Harness Find the two parts you need from the list and complete your purchase. I'll stand by until you've removed those two parts and you're ready to test....

Let me know when you have finished removing the china relay and the fried OEM ignition coil from your Rancher.

As stated earlier, the reason why all 'ell broke loose is because you installed aftermarket china parts on your Rancher. No one gets away with doing that!

Here are images of the wiring diagram and the ignition circuits diagram that I'll be referring to while testing..

Ok you'll need to buy a relay and ignition coil. You can get fair prices on OEM parts with quick shipping at Rocky Mountain ATV: https://www.rockymountainatvmc.com/oem-parts/Honda You'll find the two parts that you need on the Wiring Harness parts fiche. The ignition coil part number is 30510-HP5-601 ($56.03), it is labelled as part 1 on the parts fiche. The relay you need is labelled part 14 on the fiche, the part number is 38580-HP5-601 ($37.33). Both parts are in stock and if purchased together, shipping is fast and free. Stand by for a minute while I make a copy of the wiring diagram.....

Ok good! Remove the fried ignition coil and the china relay that you installed. Toss them both in the trash. Let me know when you're done. We'll get to that in a minute..... There is a shorted circuit somewhere. Most likely caused by one (or both) of the china parts that you installed. We see this sort of problem quite often. Daily sometimes.... China parts are garbage and can sometimes destroy other expensive parts, including wiring harnesses. Do you still have the original relay that you removed from your Rancher?

China parts cause expensive OEM parts to go up in smoke. We see this all the time. Don't worry, disconnect the battery then read back through my posts and answer my questions so we can get started on troubleshooting it.

Disconnect the negative (black) battery cable from the battery. Read the posts I've made above and answer my questions, so I can help you fix it.

@Mach 1 don't freak out, what you are experiencing is common. We see these problems weekly, sometimes daily here.... folks replace a part (or several parts) with cheap china stuff and then all 'ell breaks loose. Answer questions and follow instructions carefully and we'll probably fix it.... you'll need to buy another genuine Honda ignition coil. While you're waiting for that coil we'll diagnose the problem. Do not plug any non-OEM part in while we are diagnosing it.

Ok, unplug the china relay that you installed and remove it. Unplug the ignition coil and remove it. Toss them both in the trash can. China parts do not work on Honda's, they're garbage, and sometimes cause other expensive parts to fry. Install the original OEM Honda relay that you previously removed, if you still have it? It sounds like one of the 30 amp fuses have now blown. Check all of the fuses and let us know what you found when you've got the OEM relay back on your Rancher. We'll be doing some testing.... do you have a 12 volt test light and a decent multimeter?

Are there any parts on your Rancher that are not genuine Honda parts? We can't go any further until this question is answered.

Yep, it sounds like the Engine Stop Relay is stuck now too, since the coil fried while the ignition switch was turned off? Gotta find out if any parts have been replaced with non-OEM, replace those with OEM parts if any, then test the stop relay and the coil G/Y wire circuit and the coil B/R wire circuit. I strongly suspect china part(s).

Well that ignition coil is fried! Are there any aftermarket parts on your Rancher? Unplug that coil and don't plug it back in, you'll need to get another genuine Honda ignition coil. Do you have a 12 volt test light and a decent multimeter?

@AKATV will be along shortly RancherMan. Welcome to the forums!

I assume you've verified the fuses are all good.... a common issue I see often in my area are bad/rusty grounds. Here is an older Rancher with no spark that only had a bad ground:

Here is an image of the wiring diagram for your Rancher you can use for reference.