No power to HVAC/wiper relays

[chocolate fondue]

For the summer I'm working on my grandpa's JCB 260T and both the HVAC and wiper motor are dead. Relays click, and yes it's got coil power, but there's zero voltage at the switched terminals. There's basically no power getting to the loads. I bypassed the relays just to test and both motors work fine. Anyone got a detailed diagram I can refer to? TIA.

 

[MrWiggles01]

I think you've already ruled out the motors and relays, so its likely a wiring or control issue, maybe a bad ground or a broken feed upstream. I'd check for damaged wiring around the cab or fuse panel. As for a detailed diagram, your best bet is the JCB service manual

 

[yellowbeastPil0t]

If you want detailed wiring diagrams, the JCB 225T-330 Service Repair Manual is the place to go. It covers HVAC and wiper motor schematics and offers a comprehensive look at the electrical system, including how the fuses and relays are arranged

 

[Thecollegekid]

The relays don't actually carry the full load, they just signal through the machine's controller, which then feeds the circuits, odds are the feed isn't making it out of the controller harness. Could be a corroded pin at the main bulkhead connector or a blown fuse link feeding that bank. I'd chase power back from the relay socket with a meter and if it's dead right out of the controller, you'll probably need the service manual or wiring diagram from JCB to see which plug is feeding HVAC and wipers together

 

[Dizcaya2025]

Check the ground connections. A poor ground can look like a dead circuit. Make sure both motors are well grounded.

 

[New.yuser]

Most definitely a power feed issue, look if bypassing the relays makes the motors run, the problem is likely upstream that is the fuses, main harness, or ignition switched feed

 

[rhedsafe]

Unfortunately, the full high-resolution electrical schematic diagrams for heavy equipment like the JCB 260T are proprietary and are usually only found in the official JCB Service Manual. Your problem is specifically a missing power supply on the fused side (Terminal 30 or 87a) of the relay circuit. The fact that the relay coil (Terminals 85 and 86) is getting power and clicking confirms the control circuit (ignition, switch, fuses for the coil) is working, but the main power circuit to the load is dead.