Series 2A Diesel Glow Plug Relay

[JRT]

Hello Guys,


This is my first post so here goes.


I have 1964 Series 2a diesel and I'm 'improving' some of the wiring as I've discovered some worse for where cabling behind the dash.


The glow plugs seem to be manually switched through the ignition switch by holding the key in the position before the start position and counting to 15.


The wiring goes direct to the ballast resistor on the bulkhead and then glow plugs, which are the old pig tail type.


My question would be there is obviously no relay anywhere and that current must be going through the poor old ignition switch. Can I add a relay to take the load off the switch contacts, and still count to 15' and then start?


Would something like the relay shown be up to the job, or would I have to fit a more expensive glow plug specific relay with timer? What sort of load do the series glow plugs create?


Sorry for any duplication with anything already posted, but I can't find the exact answer yet.


Any help or information appreciated.


Cheers


JRT.

[JDNSW]

The ignition switch, as you may have noticed, is a lot beefier than the one on petrol Landrovers of similar vintage (always assuming it is original), and seeing it was designed to handle the glowplug load and has presumably done so for over fifty years, I would not see a good reason for fitting a relay. On the other hand, if you have had to replace the switch with a non-standard one, that relay would look to be quite suitable.

[JRT]

Thanks for the reply John

I'm pretty sure the ignition switch is a pattern one and not an original LR item, so I might fit that relay now I know it's suitable.

I also managed to find some NOS glow plugs made by Beru on EBay made in Germany so hopefully of good quality. I don't need them yet but no doubt will at some point.

Cheers

JRT.

[JRT]

Hello,

Well the plot thickens, with this glow plug circuit/wiring.

I am still running the old style glow plugs (pig tail) in series. So as far as I can work out they only need 1.7 V each so around 7v required. Should the ballast resistor have approximately 12v at one terminal and a lower voltage approximately 8v at other terminal ,(when measured with the ignition switch held at pre heat position)?

I seem to to have the same voltage at either end of the ballast resistor, and 2 glow plugs have failed ( too much voltage I guess).

Am I looking at this too simplistically or is something wired up wrong?



I had a further search on the forum, and I have found the answer! It's me being a 'dullard'

There is a post on here which explains the wiring and reminded how series circuits works .....The post is titled 'Glow Plugs' in the Series II,IIA forum.....thanks to the contributors as it helped the penny drop for me


Cheers

JRT

[JDNSW]

The ballast resistor will only drop the voltage when the design current is flowing. In the case of the old type heater plugs, these need to be wired in series with both each other and the ballast resistor. When 12v is applied to this you will find that the voltage across each heater plug is approximately correct.

If two glow plugs have failed, since they are in series, no current is flowing.

You need to check that you actually do have them all in series, and that you do not have an accidental short to earth somewhere that may have led to getting the 8v across only two plugs.

[JRT]

Thanks for the reply John.

I appreciate your guidance on this, and I'll have a look tomorrow for any shorts to earth as you describe.

The only other query I have is the glow plug 'bulb' on the dash, and I take it illuminates only when that circuit is complete and dims when the plugs are all working/heating. If it stays bright when the ignition switch is in the heat position, am I right in thinking it's got a short to earth, and not going through all the glow plugs?

Thanks again.

Cheers

JRT

[JDNSW]

Thanks for the reply John.

I appreciate your guidance on this, and I'll have a look tomorrow for any shorts to earth as you describe.

The only other query I have is the glow plug 'bulb' on the dash, and I take it illuminates only when that circuit is complete and dims when the plugs are all working/heating. If it stays bright when the ignition switch is in the heat position, am I right in thinking it's got a short to earth, and not going through all the glow plugs?

Thanks again.

Cheers

JRT

It is over fifty years since I have owned a diesel 2a, so my memory may not be perfect, and I can only quote the owner's manual -"The amber warning light ...will glow when the heater plug switch is operated; this indicates that current is being passed to the heater plugs; there is a delay of two or three seconds before it glows. If the warning light glows more brightly at any time, a short circuit in the system is indicated*. No light will indicate an open circuit."

*This would also be the case if the plugs were incorrectly wired in parallel; or if there is a short to earth connecting only one or two plugs to the system - for the few seconds before they burnt out.

Note that the warning light and ballast must be connected on the plug side of the relay, not between the switch and the coil of the relay.

Hope this helps.

[JRT]

Thanks John

Really helpful advice, greatly appreciated.

I'll post an update soon.

Cheers

JRT