This write-up will explain the use of a Volvo 740 glow plug relay found on some Volvo models with the 6-cylinder 2.4 liter IDI engine built by Volkswagen, in 4-cylinder applications. I have been using this relay for several weeks now on a 1.6 IDI turbodiesel engine installed in a 1992 Jetta.
This is the relay:
Relay as installed in its original Volvo application:
Advantages of using this relay instead of the stock VW relay or other systems:
1. More robust design with screw terminals and locking female connector instead of the fragile VW design with push-in spade terminals.
2. Higher ampere rating.
3. Much easier to install in applications which did not have a provision for any glow plug relay(such as Suzuki Samurai or gas VW) because it does not require a special socket like the VW relay does and is designed to be mounted to the body of the vehicle, under the hood. The relay has 2 holes to attach it.
4. Works the same way as the fast VW relay but is a different design, the Volvo cars use the same 80010 Bosch plugs so it's designed for the same system but is manufactured differently. Works in any VW IDI diesel when the "fast" glow plugs are used.
5. Has a built-in fuse holder eliminating the need for a separate fuse holder.
6. Cycles the glow plugs for a slightly longer interval compared to the VW relay- 7 seconds up to 30 seconds depending on temperature.***
7. Completely automatic, operates only when engine is cold, same as the OEM VW system.
8. Larger internal conductor components, less resistance and voltage drop.***
***Note, this is theoretical. I determined this by testing the relay with a constant 12 volt power source, and NO glow plug load. I'm not sure if the real-world performance is different.
Disadvantages of the Volvo glow plug relay.
1. Expensive, but used ones can be found on ebay. They rarely fail though. I am using one that's 20 years old.
2. Hard to find in the U.S., apparently only sold online and not available at "normal" parts stores. Not the same as earlier 240 diesel cars.
3. Requires a connector that is easily obtainable but used only in Volvos. Pins are not the same size as similar connectors found on other cars.
Using the Volvo glow plug relay:
Volvo glow plug relay installed in a Jetta originally equipped with a gasoline engine.
You will need:
1 glow plug relay
Wiring connector - obtain square 4 pin female connector socket from a Volvo (they are used on some underhood relays found on some gas 740s and 940s). However, these cars have a common problem where the wiring often becomes extremely brittle and disintegrates, so you may need to buy new parts which can be found inexpensively on
http://www.davebarton.com/blackvinyl.html or on ebay. They are however, expensive at Volvo dealers. You need a female square 4-pin connector shell and 4
female sealed bullet terminal wire inserts with pigtails. You can then assemble the connector or rebuild the old connector with Volvo part number 3523813 (pigtail). The connector shell comes apart to install new wires. Tabs at the end of the socket the two halves of it together.
This is how it is connected and the pin-outs:
Above image represents the connections as they are found
on the relay. You will need to wire the connector to match.
There are 5 connections in addition to the battery (+) and glow plug load, for which you will need 8 gauge or thicker wire and ring connectors.
- ignition switch start AND run, tells relay to turn on, needs constant power in RUN and START too to keep relay from cycling.
- starter solenoid, powered in START only, turns off glow plug operation if starter is activated too soon.
- 5+ volt output to ground at sending unit/sensor, uses the same sending unit/sensor as VW diesels.
- glow plug indicator lamp, note this
grounds a lamp connected to a constant power source (should be powered only when ignition is ON).
- relay ground, the relay needs a good ground.
Use at least 14 gauge wire for the ground but the rest can be 16-18 gauge because the relay draws less than 0.5 amp.
This is all the same as the VW system. I had to deduct this information experimentally by connecting the different terminals to a 12 volt power supply as I could not find any information online about the relay pin-outs but was able to figure it out without damaging my relay.
I am also using sending unit/sensor 1H0-919-563 instead of the OEM sensor which is listed as an oil temperature sensor but is physically and electrically similar (enough) to work with the relay, but has a more user-friendly spade terminal.
The reason I did this is because I was using the normal VW glow plug relay but had a relay failure which resulted in the glow plugs cycling when they weren't supposed to, and before that had problems with the spade terminals loosening (though the relay was not installed in the fuse box) causing bad connections. I did not want to spend money on a $50 relay that I thought was a problematic design, that looked bad because it was loose with no means to attach it to the firewall, and did not want to use a manual cycling system. Using the Volvo relay seemed to give me what I needed. I would recommend installing a Volvo glow plug relay if you would like to improve your existing VW glow plug system or would like to install a fully automatic glow plug relay in any VW IDI diesel powered car which originally did not have a diesel engine.