Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Speedo jumping.

Thank you gentlemen, now it makes sense and thanks for your combined patience with this matter.

Good morning Gents,

Update so far,

After a long wait the new relay and 20 fuses arrived ( fuses just in case ).
Fitted relay the correct way 85 to ground, all was well no fuses blowing this time, however I am back to the original situation which is when the side lights are switched on the speedo jumps to 40 mph and then returns to zero.

This is with a relay incorporating a diode.

All other aspects work perfect drl's swich off when side lights are switched on, side lights ok, head lights ok,indicators and hazards ok.

I'm at a loss now, the question is will this cause any major problems if left as is. I could live with the jumping speedo if needed.

Any ideas chaps?

Rob.

Blimey Rob this one just won’t lie down! From what you say you have done now all sounds good to me. Out of curiosity it would be interesting to know if it’s the relay coil or the circuitry in the switchback bulbs that is generating a spike. One little test would be to temporarily disconnect either 87 or 30 from the relay (disconnect the DRL's). If it still jumps then the relay is still suspect but if it doesn’t then the circuitry in the switchback bulbs may be somehow causing it.

Hi Roger, I will try this tomorrow and report back.

Just a note, I am using 87A and 30. 87 is redundant, as I understand it the drl's use 87A to be live as the ignition is on and when the side lights power up the relay throws power over to 87 therefore killing the drl's. Is this right?


Rob.

Yep sounds good.

Roger, if all else fails I could run the DRL's via a switch from the relay and forget about the side lights connection, not as good as automatic switching off but a solution of sorts.

Do you think leaving things as is with the spike could cause long term damage? If not I could live with the spike.


Rob..

Well that was a thought that I had too. The proximity of the speedo’s internal bulb (that is connected to the lighting circuit) with respect to the speedo’s internal sensitive electronics maybe the noise pathway, so powering the DRL’s from a separate switched supply ‘might’ solve it. It would be easy to check out.

Long term damage….? If it’s just radiated noise I don’t think so but the experts here may have a different opinion?

Good morning Roger,

Update so far:

Disconnected DRL's (pin 30) started the car, put lights on and a spike this time to only 15mph.

Switched lights off and on again no spike, turned the car off and restarted, switched the lights on spike to 15mph again.

Turned the car off again, restarted, switched the lights on, no spike tried switching the lights on and off about 6 times and no spike.

Re connected the DRL's, started the car, DRL's came on, turned on the lights, no spike. Tried the lights on and off about 6 times and no spike.

Strange things these Morgans.


Rob..

And...can we assume the speedo still works??

Yes Doug all works as normal.