Ford Transit Custom Campervan Electrical System Guide
The Ford Transit Custom is the UK's best-selling van and one of the most popular bases for smaller campervan conversions. Its compact dimensions, comfortable driving position, and versatile loadspace make it ideal for weekend conversions and micro-campers. The electrical system, however, has some important characteristics to understand before you start — particularly around the alternator and how charging works.
This guide covers everything electrical and specific to the Transit Custom. For the full component guide, see our campervan electrical system overview. Use the free calculator to size your system.
Size your Transit Custom electrical system
Our calculator builds a complete specification for your Transit Custom conversion based on your usage and appliances.
Transit Custom Smart Alternator
All Ford Transit Custom models from 2012 onwards use a smart alternator (Ford calls it "Intelligent Energy Management" or IEM). Like all modern smart alternators, it does not run at a fixed voltage — it adjusts output to prioritise fuel economy and braking energy recovery.
This means the alternator voltage can be anywhere from 12.5V to 14.9V, and Ford's IEM system often intentionally suppresses alternator output when it decides the battery is sufficiently charged.
Bottom line: a split charge relay will not reliably charge a leisure battery in a Transit Custom. The unpredictable voltage signal causes the relay to chatter (open and close rapidly) or never trigger at all.
A DC-DC charger is essential. It takes whatever the Transit Custom alternator provides and converts it to a proper charge profile for your leisure battery chemistry (AGM or LiFePO4).
Wiring the DC-DC Charger Input
In the Transit Custom, the standard approach is to run the DC-DC charger's vehicle-side input to the engine bay fuse box. Ford provides auxiliary fuse positions in the Transit Custom fuse box — consult your workshop manual for your specific year to find a suitable unswitched 12V feed.
Alternatively, run directly to the vehicle's battery positive with an appropriate inline fuse, using the van's existing bulkhead grommets to route into the loadspace.
Recommended DC-DC chargers for the Transit Custom:
- Renogy 30A DCC30S (~£140) — popular, reliable, Bluetooth
- Victron Orion-Tr Smart 30A (~£220) — premium, full app integration
- Sterling Power BB1260 (~£180) — established brand, well-regarded
See our DC-DC charger size guide for choosing the right amperage.
Battery Placement in a Transit Custom
The Transit Custom load area is smaller than a full-size Transit or Sprinter. Common battery placements:
Under the Passenger Seat
The Transit Custom's front passenger seat typically sits on a base with accessible space beneath. A 100Ah or slim-profile 200Ah battery fits here on most configurations. Advantages: weight forward and low, easy access, does not eat into loadspace.
Bulkhead Cabinet
Many Transit Custom conversions build a small cabinet against the bulkhead between cab and loadspace. A battery cabinet here uses space that would otherwise be dead, keeps weight central, and provides easy wiring access to the cab area.
Under a Raised Bed Platform
On conversions with a fixed lengthways bed, the space under the platform is the most common battery location. Accessible via a hatch or sliding panel. Less convenient but keeps the floor area clean.
Battery Size for the Transit Custom
The Transit Custom's shorter load length (SWB: 1,686mm) limits full-time-living system size, but for weekend and holiday use it is very capable:
| Use Case | Battery | Notes |
|---|---|---|
| Micro-camper / weekend | 100Ah LiFePO4 | Ideal for small builds |
| Regular holiday use | 200Ah LiFePO4 | Sweet spot for Transit Custom |
| Serious multi-week | 2 × 100Ah LiFePO4 | Wired in parallel, space-efficient |
Solar on a Transit Custom
The Transit Custom roof is short. On a standard LWB variant, the usable flat area is approximately 100cm × 80cm — enough for one 100-150W rigid panel, or potentially 150W with a slim-profile panel.
Standard Roof
A single 100W or 120W rigid panel is the most practical choice. Some builders use a 150W compact panel (typically 142cm × 67cm) which fits well on the Transit Custom roof. This gives 300-400Wh per day in UK summer.
High Roof
The Ford Transit Custom is available in a high-roof variant. This adds significant roof area and allows 200-250W of solar, plus standing height in the conversion.
Solar Cable Routing
Run solar cables through the roof using a proper cable entry gland — see our solar cable gland guide. The Transit Custom has thin roof sheet metal, so use appropriate self-tapping fixings for the gland, with sealant and butyl tape for waterproofing.
Route cables inside the van through the headlining channel down the A-pillar or B-pillar, then under the cladding to the charge controller.
Shore Power
For a Transit Custom micro-camper that will visit hook-up sites regularly, adding shore power is worthwhile. The most practical position for the shore power inlet (CEE blue socket) is the nearside rear corner, which is accessible when parked at a hook-up post.
A basic shore power setup — inlet, consumer unit with RCD and 1-2 MCBs, and a 230V socket — costs around £150-200 in parts and does not take long to install. See our shore power setup guide and consumer unit wiring guide.
Example Transit Custom Builds
Micro-Camper (SWB, occasional weekends)
| Component | Spec | Cost |
|---|---|---|
| Battery | Fogstar Drift 100Ah LiFePO4 | £299 |
| DC-DC Charger | Renogy 20A | £120 |
| Solar | 100W panel + 20A MPPT | £110 |
| Fuse Box | 6-way blade | £15 |
| Battery Monitor | Basic shunt monitor | £30 |
| Wiring | Cable, fuses | £80 |
| Total | ~£655 |
Comfortable Weekend Camper (LWB)
| Component | Spec | Cost |
|---|---|---|
| Battery | Fogstar Drift 200Ah LiFePO4 | £549 |
| DC-DC Charger | Victron Orion-Tr Smart 30A | £220 |
| Solar | 150W panel + 20A MPPT | £160 |
| Inverter | 1000W pure sine wave | £130 |
| Consumer Unit | Basic RCD + MCB shore power | £120 |
| Battery Monitor | Victron SmartShunt | £60 |
| Wiring & Sundries | £180 | |
| Total | ~£1,420 |
Transit Custom-Specific Wiring Notes
Cab Accessories
The Transit Custom has a 12V accessory socket in the dashboard. This is fused at 20A and suitable for powering a dash cam, phone charger, or similar low-draw accessory. Do not use it as a feed for the leisure system.
Central Locking and Alarm
Some Transit Custom alarm systems monitor current draw on the vehicle battery. Fitting a large DC-DC charger or leisure system without informing the system can occasionally trigger false alarm events. If this occurs, consult a Ford specialist — it is usually resolved by adjusting the alarm sensitivity.
Rear Door Wiring
If fitting lights in the rear load doors, use flexible cable with adequate service loops at the hinge points. The Transit Custom load door hinges experience significant movement — rigid cable runs will fatigue and fail within months.
FAQ
Does the Transit Custom use the same alternator as the full-size Transit?
Different engine variants use different alternators, but all Transit Custom models from 2012 have smart alternator management. Treat all Transit Custom models as requiring a DC-DC charger regardless of year.
Can I fit a 200Ah battery in a SWB Transit Custom?
Yes. The Fogstar Drift 200Ah (522mm × 238mm × 218mm) fits under a rear platform or in a bulkhead cabinet. Measure your specific conversion layout first — SWB is tighter than LWB.
What is the maximum solar for a standard-roof Transit Custom?
Practically, 150-180W on a standard LWB roof. The short roof is the limiting factor. High-roof variants can accommodate 200-250W.
Is the Transit Custom good for a full-time campervan?
It is a compromise. The SWB is very tight for full-time living. The LWB offers more usable space but is still smaller than a Sprinter, Transit (full-size), or Crafter. Many full-timers upgrade from a Transit Custom to a larger base after their first conversion. That said, plenty of people do live full-time in a well-built Transit Custom, particularly solo travellers.