Combining Hella Single Relay kit w/Westy Fridge


New member
I read through the diagrams of the Westy on Capt. M's home page, and through most of the boards. Very helpful. However, I am at a loss with this one.

I converted an icebox to a refridge in a '76 Westy, it works great on AC, followed Capt. M's Bentley instructions, and works beautifully.

Now it is time to install the aux. battery. The two wires I have left from the Westy control panel are a black and a white. I have them waiting in the engine compartment.

1) I purchased the Hella 4RA 003 LGE 141 Single Relay Kit: Battery or Fridge in order to connect the two batteries properly. The hand-written section from the Bentley guide have a TOTALLY different scheme than the Hella directions. However, the relay post numbers do match.


1) Does anyone know the difference and why these diagrams don't match?

2) Where do the black and white wires from the control panel go? (not the inverter white wire - got that from diagram)

3) The Hella directions say "Connect to Pin 2 for auxilary battery charging or Pin 6 for refrigerator. What pins are they referring to?

4) The Hella directions show a dotted line to the pos. terminal on the aux. battery. With a note under it "Dotted line shows alternative wiring, if preferred, for charging auxiliary battery in the boot via sing pole plug and socket (not supplied)."
This is wire from term. 87 on relay which stops at "12/7S Socket". Not too sure what that is, and why does the ONLY wire leading to the aux bat. Positive have a note saying that it is "alternative wiring if preferred"?

5) Will this "Hella" wiring diagram allow me to use the aux. power without killing my primary battery?

6) When I set the timer on the control panel, is it designed to charge both batteries, if the primary is low as well?

My apolgies for the long-windedness! I tried to be as succinct and descriptive as I could. I'm getting very excited about this, but want the battery to function and charge properly

I certainly owe a beer to whomever can crack this case!

Thanks in advance!

Capt. Mike

I can't comment on the Hella wiring diagram, not having seen it, but since it is not OE to VW, any similarities will be just because Hella and VW both tend to use the same industry standard markings -- in fact Hella oftens supplies VW with parts.

The original US supplier for VW converters and Westy equipment seems to have had an unlimited supply of black & white wire, but none of the usual color codes used by VW, such as brown for ground. Per wiring diagram 97.4 in the out-of-print Repair Manual Type 2 (posted on the Tech Drawings link) they used white & black for everything, including feed from the auxiliary battery. The OE harness used a red wire from the auxilary battery to the in-line S4 16a fuse (fused entire aux. battery), which then turned to black to enter the Westy electric control panel. The return (ground) was white.

I would presume Hella, in using the term "pins" is talking about a wiring scheme that uses a multi-plug. VW used T2, T3 & T4 wire connectors, but these were invariable the spade type conecters to connect either 2 wires together, or provide a multiple connection for branching a circuit.

"Alternate wiring" is found on vehicles that have multiple markets where there are changes that still use common parts. For example, Porsche used one wiring scheme for US bound models to cut the fog lights out when going to high-beam; the European version left them on. Thus an "alternate" wiring diagram. I have found several unused wires in other vehicles for versions & accessories not included in mine. It is cheaper to make a harness with unused parts than to have two separate harnesses for the two markets.

Hella is pretty consistent with terminal numbering. In the case of a relay, #30 is typically the power from the battery; #87 power out to the appliance. #86 is generally the switching power (in the P27 case, from the alternator) and #85 the relay ground. In the case of putting batteries in parallel, #30 is from the main battery and #87 to the auxiliary.

Properly connected the relay allows you to use the auxiliary battery without killing the main. All fridge power is from the auxiliary. The only time it is cross-connected to the main is while the engine is running, thus feeding power from the alternator lead to terminal #86 to close the relay switch. However, this isolation also means that recharge is only charging the auxiliary. The one Hella option you mention (#4) might be a means to recharge the auxiliary from an external source that normally supplies the main. Socket style external battery chargers and jumper wiring were a popular accessory for a few years. Many RVs (this relay's market) have permanent charging circuitry to AC built in.

When attempting to use non-OE parts, you generally have to go back to the basics. Which contacts in the relay activiate it? Which connect the appliance power? How does your replacement equipment feed the original fridge and control panel. I put an AC converter into a '90 Vanagon I outfitted with the auxiliary battery. OE manufacturer, but some slight differences (they now have a roll of red and a roll of blue wire). I didn't get an OE control panel but created the charging timer and battery monitor gauges from items that use the same principles. Since a Vanagon has the AC/DC/LPG switch built in to the fridge, I didn't need the AC/DC switching circuitry (E3 in diagram). I put the E4 switch at the new monitor gauge. The E1 timer is independent so I have no "control panel."

But, because I still use the OE relay system, to recharge the main off AC, I carry a small jumper cable (only one -- don't need a ground jumper since they are both permanently grounded to the chassis).


New member
Capt. Mike,

THANKS! I appreciate the thorough 'homework'. Your solution worked like a charm, particularly 5th paragraph.

The van passed all charging/relay/aux battery tests with flying colors. Not even one blown fuse! The descriptions of the Hella Pin #'s were dead on, and from there, just followed your diagram for a P-27 in your briefcase.

Again -- thanks, I'm really psyched to see this in action. I switched between 'city' and 'battery' power about 20X !!