3100 / 3400
98-99 3100/3400 Simplfiied wiring harness
98-99 GM 3100/3400 V6. Runs on a 98–05 tuned ECM. Power and ground hookup.
$300.00Shop
573-578-6347•All-new wire & connectors•Simple 2-wire hookup•Built to order in Rolla, MO•Derby / race / off-road use only•Free troubleshooting help•
Simplified standalone wiring · Rolla, Missouri
Plug it. Send it.Win it.
Standalone harnesses built with all-new wire and connectors, with every unnecessary factory circuit deleted. Power it, ground it, flip two toggles and go — for derby cars, race builds, swaps, mud trucks and off-road projects.
- All-new wire & connectors
- Simple 2-wire hookup
- Built to order in Missouri
- Free troubleshooting help
0parts in the catalog
0engine families covered
0wires to get it running
0harness repair & diagnostic
[ 01 ] Shop by engine
Pick your engine family
Harnesses, tuned ECMs, injector adapters and brackets — organized by what's sitting in your build.
[ 02 ] Two questions
Find your harness
Tell us what you're running and we'll point you at the exact harness — plus the tuned ECM it needs.
Not sure, or running something odd? Call 573-578-6347 — custom builds are normal around here.
[ 03 ] How it runs
Three moves and it's alive
- 01Power and groundRed wire is 12V. Black wire is a solid ground to clean, bare metal — paint isn't a conductor. That's the whole hookup.
- 02Flip the togglesToggle one is ignition power. Toggle two is the fuel pump. Hear the pump hum and you've got fuel.
- 03Hit the buttonPush button triggers the starter. Spark plus fuel equals party time — no keys, no VATS, no body harness.
[ 04 ] Simplified standalone harnesses
Built new. Not resurrected.
Every harness is assembled from brand-new wire and connectors — no brittle insulation, no worn junkyard terminals, no circuits you'll never use. Tuned ECM sold separately unless noted.
3100 / 3400
2000–2005 GM 3100/3400 Simplified Harness — ECM & Injector Adapter Sold Separately
00–05 GM 3100/3400 V6. Runs on a 98–05 tuned ECM. Power and ground hookup.
$300.00Shop
3800
98-05 3800 Simplified wiring harness
Series II 3800. Works with older engines when paired with a 98–05 ECM. Adapters available.
$330.00Shop
2.2 SFI
1997-2001 GM 2.2 SFI Simplified harness
Two basic connections and the 2.2 runs. Stripped-down builds, derby cars, off-road.
$400.00Shop
Ecotec
02-05 2.2 Ecotec harness
Simplified Ecotec standalone. Only two wires needed for basic operation.
$330.00Shop
LS · DBW
03-07 LS Drive-By-Wire Standalone Harness
4.8 / 5.3 / 6.0 with green or blue PCMs. GM Delphi connectors, TXL high-temp wire. TAC module required.
$475.00Shop
LS DBC
99-02 LS Drive-By-Cable Standalone Harness
DRIVE BY CABLE LS HARNESS, FLIPPED INTAKE SETUP AVAILABLE!
$425.00Shop
3800 SERIES II SC
1998–2005 GM 3800 Supercharged L67/L32 Simplified Harness — ECM Sold Separately
98-05 3800 SERIES 2 SUPERCHAGED HARNESS
$330.00Shop
3500 LX9
2004-2006 3500 LX9 Simplfiied Harness
Labeled connections, standalone operation, no factory body wiring. The popular step up from a 3400.
$450.00Shop
3100 / 3400
GM 3100 Simplified Wiring Harness — For 1996–1997 Tuned ECM
96-97 SIMPLIFIED HARNESS
$300.00Shop
Why new wire
Less hassle.More throttle.
Twenty-five-year-old factory harnesses fail in the ways that end a night: cracked insulation, green terminals, a chafed wire buried under loom, a body computer that wants a key it will never see again.
We delete all of it. Unnecessary circuits gone, sensors that only cause shutdowns disabled on the tune side, connections labeled, and the whole thing rebuilt in new wire so the only thing you're chasing at the track is the car in front of you.
- Unnecessary factory circuits removed
- Labeled connections, new loom
- Durable enough for derby and mud
- Off-road / competition use only
[ 05 ] Derby tunes
Tuned ECMs that refuse to quit
Timing and fueling optimized, rev limiter raised, temp limits pushed up, VATS security removed and shutdown-happy sensors disabled — so the engine keeps running when things get hot and rough.
3100 / 3400
1998–2005 GM 3100/3400 Tuned ECM — No Core Required
1998–2005 derby tune. Works with the factory harness or an LMMF simplified harness.
$130.00Shop
3800 Series 3
04-08 Series 3 3800 tuned ecm
Runs on the stock harness with a push-button start and a hotwired fuel pump.
$200.00Shop
LS · DBW
2003-2007 LS TUNED ECM 4.8/5.3/6.0. DBW
4.8 / 5.3 / 6.0 drive-by-wire. Pairs with the 03–07 LS standalone harness.
$200.00Shop
[ 06 ] Matched packages
Harness plus ECM, already matched
Stop cross-referencing part numbers. Bundles ship as a set: simplified harness, a tuned ECM matched to your setup, and the injector adapter it needs.
Most ordered
1996–2005 GM 3100/3400 Harness + Tuned ECM Package — No Core Required
Simplified harness, tuned ECM matched to your setup, injector adapter. Ready to run.
$495.00Shop
3800 Series II
1998–2005 GM 3800 Series II Harness + Tuned ECM Package — No Core Required
Simplified 3800 harness paired with its tuned ECM for a Series II swap.
$460.00Shop
Early 3100
1989–1999 GM 3.1 / 3100 Harness + Tuned ECM Package — No Core Required
For the older 3100 cores — harness, matched tune and adapters in one order.
$525.00Shop
[ 07 ] Control & hardware
Everything else the build needs
Switch boxes, brackets, hotwires and adapters built with the same connectors and wire that go into the harnesses.
3100 / 3400
LMMF Party Mode Temp Sensor Override Switch — GM 2-Pin / 3-Pin Universal
Override overheat protection and keep it running to the last hit.
$120.00Shop
3100 / 3400
LMMF Adjustable 3100/3400 throttle bracket
Built for aftermarket throttle setups.
$45.00Shop
3100 / 3400
3100/3400/3800 Extended Length Heavy duty spark plug wires
Extended-length sets available for relocated coils.
$40.00Shop
3100 / 3400
2000-2005 3100/3400 injector harness
Plus EV1/EV6/Multec adapter pigtails from $3.
$95.00Shop
[ 04 ] Simplified standalone harnesses
Built new. Not resurrected.
Every harness is assembled from brand-new wire and connectors — no brittle insulation, no worn junkyard terminals, no circuits you'll never use. Tuned ECM sold separately unless noted.
[ 08 ] Verified storefront reviews
Ran it. Sent it.
★★★★★"If you're building on a budget, and wanna have fun but still compete these things are great. Will for sure be buying more of these guys."
★★★★★"Great product. Worked great and car performed so good with this ecm."
★★★★★"Works great. Just plug and play!"
★★★★★"Got my car to run again."
★★★★★"Very easy install and fast shipping."
★★★★★"Great customer service. Arrived fast — good quality."
Reviews collected on lmmfsimplifiedwiring.com through Judge.me. See every review on the storefront.
Let customers speak for us
Great customer service
Great customer service ,
Chris Kirves
Arrived
Arrived fast
Chris Kirves
Yes fast received and good
Yes fast received and good quality
Chris Kirves
Great
Great shopping
Brian
Great product
Great product. Worked great and car performed so good with this ecm.
Brian
Got my car to run
Got my car to run again
Anonymous
Perfect for a aftermarket throttle set
Perfect for a aftermarket throttle set up
Evan Hoyle
Fits a 3100/3400 coil
Fits a 3100/3400 coil perfectly
Evan Hoyle
If you’re building on a budget
If you’re building on a budget, and wanna have fun but still compete these things are great. Will for sure be buying more of these guys.
William Housewright
Works great thank
Works great thank you
Anonymous
Lmmf great company definitely will be buy more great customers service
Erick
This harness looks fantastic
This harness looks fantastic. I'm very happy so far l have not installed yet .
Jeff Rettig
.
James Walton
Very easy install and fast shipping
Very easy install and fast shipping.
Dana Wessel
Awesome product
Awesome product. Ready to test it out on July 18
Dana Wessel
[ 09 ] Services & support
Send us the problem child
Two ways we work on harnesses you already own — plus a phone number that actually gets answered.
Harness Repair & Diagnostic $25.00
Reserves your repair order and covers the full inspection: overall condition, wiring damage, connector damage, previous repairs, and whether it's repairable. You get an estimate before any work happens, and the fee includes return shipping.
4.2 Trailblazer / Envoy core rebuild $350.00
Ship us your complete 2002–2005 4.2L Atlas harness. We strip the unnecessary circuits, simplify, label and re-loom it in new braided loom, then ship it back needing only power, ground, fuel pump and ignition.
Common questions
Do I need a tuned ECM too?
For most simplified harnesses, yes — the harness and tune work as a pair, and the tune is what removes VATS security, raises the rev limiter and stops shutdown-happy sensors from killing the engine. Each harness listing states which ECM it runs on, and bundles ship with a tuned ECM matched to your setup.
Will this work on my street car?
No. These harnesses and tunes are intended for off-road, race, and demolition derby use only.
What does "2-wire hookup" actually mean?
Once the harness is on the engine, basic operation needs 12V power and a solid ground. Ignition, fuel pump and starter get triggered from toggles and a push button — which is exactly what our switch boxes are built for.
My harness is installed and it won't start.
Work the no-start checklist: 12V on the red wire, ground on the black wire to clean bare metal, ignition toggle on, fuel pump toggle on, push button cranking. Full walkthrough lives on the troubleshooting page, and install guides are here.
Can you build something that isn't listed?
Usually. Call or text 573-578-6347 with what you're running and what you want it to do.
[ 10 ] Pit gear
Wear it to the fairgrounds
From the shop floor to the last hit. LMMF pit gear is for the drivers and crews who build hard, run hard, and wear it to the fairgrounds.
