AM138537 S500-B100 Glow Plug Relay Module, 12V 40A, 4-Terminal Diesel Preheat Controller, Replaces OE AM138537, Compatible with John Deere 655 755 756 855 856 F915 F925 F935

AM138537 Glow Plug Relay Module (Replacement Part) Replacement glow plug relay/module for diesel pre-heat circuits. Designed to match applications that specify OE AM138537. Confirm compatibility by OE number and your equipment manual/parts catalog before ordering. Key specifications: OE reference: AM138537 (module label may also show 194437-0000) Electrical system: 12V pre-heat circuit (rating varies by application; verify your manual) Terminals: 4 blade terminals (match terminal layout/wiring) Function: switches glow plug power during preheat to support cold starts Common symptoms (may vary): Hard cold starts or extended cranking No preheat indicator or inconsistent preheat operation Installation notes: Disconnect battery before service Inspect terminals for heat damage/corrosion; clean and tighten connections Install fully seated; verify wiring matches your original layout before reconnecting power If symptoms remain, inspect glow plugs, fuses/links, wiring, and the preheat timer/control circuit Compatibility reminder: Compatible with John Deere equipment that specifies OE AM138537 (examples often listed: 655, 755, 756, 855, 856, F915, F925, F935). If your OE number or terminal layout differs, do not install. Brand/model names are used only to indicate compatibility.

• Specs & key benefits: Replacement 12V glow plug relay module / diesel pre-heat controller with 4 heavy-duty blade terminals; compact size 2.5"L x 1.2"W x 1.2"H, ~0.14 lb. Often cataloged as a 40A pre-heat module used to switch power to the glow plugs during cold-start preheat (timing is controlled by your equipment's preheat circuit). Helps address common preheat-related issues such as hard cold starts, extended cranking, or no preheat indicator (symptoms vary). OE reference: AM138537; module label commonly shows 194437-0000. Match by OE number + terminal layout before ordering; if your part number differs, do not purchase.
• Install notes: Disconnect battery before service. Locate the glow plug module on the diesel pre-heat circuit, commonly listed as a main wiring harness/under-hood module on many compatible machines. Pull the old module straight off its mount/terminal block, inspect the 4 terminals for heat damage or corrosion, and clean/tighten connections as needed. Install the new module fully seated; verify your wiring matches the correct terminal layout before reconnecting power. After install, test preheat indicator and cold-start behavior; diagnose glow plugs, fuse, wiring, or timer circuit if symptoms remain.
• Compatible with 1986-1990 John Deere 655 Engine Compartment Glow Plug Module Relay; Compatible with 1986-1998 John Deere 755 Engine Compartment Glow Plug Module Relay; Compatible with 1986-1998 John Deere 756 Engine Compartment Glow Plug Module Relay; Compatible with 1986-1998 John Deere 855 Engine Compartment Glow Plug Module Relay; Compatible with 1986-1998 John Deere 856 Engine Compartment Glow Plug Module Relay. Confirm fitment by OE AM138537 on your existing module and your equipment parts catalog.
• Compatible with 1987-1992 John Deere F915 Under Hood Glow Plug Module Relay; Compatible with 1993-2000 John Deere F925 Under Hood Glow Plug Module Relay; Compatible with 1986-2000 John Deere F935 Under Hood Glow Plug Module Relay. Confirm fitment by OE AM138537; if your machine uses multiple glow plug electrical components, matching the exact OE number is the safest way to confirm.
• Related parts & troubleshooting: Glow plug modules are only one piece of the starting system. For best results, also inspect/replace worn glow plugs, pre-heat wiring harness connectors, fuses/links, battery cables, and the preheat switch/timer circuit (depending on your equipment). If you're stocking spares, this module is commonly kept as a backup in the tool box for diesel equipment that relies on glow plug preheat. Always confirm by OE AM138537 plus the 4-terminal layout to avoid ordering the wrong electrical part.